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diff --git a/src/wal.c b/src/wal.c new file mode 100644 index 0000000..fdc4ac3 --- /dev/null +++ b/src/wal.c @@ -0,0 +1,4155 @@ +/* +** 2010 February 1 +** +** The author disclaims copyright to this source code. In place of +** a legal notice, here is a blessing: +** +** May you do good and not evil. +** May you find forgiveness for yourself and forgive others. +** May you share freely, never taking more than you give. +** +************************************************************************* +** +** This file contains the implementation of a write-ahead log (WAL) used in +** "journal_mode=WAL" mode. +** +** WRITE-AHEAD LOG (WAL) FILE FORMAT +** +** A WAL file consists of a header followed by zero or more "frames". +** Each frame records the revised content of a single page from the +** database file. All changes to the database are recorded by writing +** frames into the WAL. Transactions commit when a frame is written that +** contains a commit marker. A single WAL can and usually does record +** multiple transactions. Periodically, the content of the WAL is +** transferred back into the database file in an operation called a +** "checkpoint". +** +** A single WAL file can be used multiple times. In other words, the +** WAL can fill up with frames and then be checkpointed and then new +** frames can overwrite the old ones. A WAL always grows from beginning +** toward the end. Checksums and counters attached to each frame are +** used to determine which frames within the WAL are valid and which +** are leftovers from prior checkpoints. +** +** The WAL header is 32 bytes in size and consists of the following eight +** big-endian 32-bit unsigned integer values: +** +** 0: Magic number. 0x377f0682 or 0x377f0683 +** 4: File format version. Currently 3007000 +** 8: Database page size. Example: 1024 +** 12: Checkpoint sequence number +** 16: Salt-1, random integer incremented with each checkpoint +** 20: Salt-2, a different random integer changing with each ckpt +** 24: Checksum-1 (first part of checksum for first 24 bytes of header). +** 28: Checksum-2 (second part of checksum for first 24 bytes of header). +** +** Immediately following the wal-header are zero or more frames. Each +** frame consists of a 24-byte frame-header followed by a <page-size> bytes +** of page data. The frame-header is six big-endian 32-bit unsigned +** integer values, as follows: +** +** 0: Page number. +** 4: For commit records, the size of the database image in pages +** after the commit. For all other records, zero. +** 8: Salt-1 (copied from the header) +** 12: Salt-2 (copied from the header) +** 16: Checksum-1. +** 20: Checksum-2. +** +** A frame is considered valid if and only if the following conditions are +** true: +** +** (1) The salt-1 and salt-2 values in the frame-header match +** salt values in the wal-header +** +** (2) The checksum values in the final 8 bytes of the frame-header +** exactly match the checksum computed consecutively on the +** WAL header and the first 8 bytes and the content of all frames +** up to and including the current frame. +** +** The checksum is computed using 32-bit big-endian integers if the +** magic number in the first 4 bytes of the WAL is 0x377f0683 and it +** is computed using little-endian if the magic number is 0x377f0682. +** The checksum values are always stored in the frame header in a +** big-endian format regardless of which byte order is used to compute +** the checksum. The checksum is computed by interpreting the input as +** an even number of unsigned 32-bit integers: x[0] through x[N]. The +** algorithm used for the checksum is as follows: +** +** for i from 0 to n-1 step 2: +** s0 += x[i] + s1; +** s1 += x[i+1] + s0; +** endfor +** +** Note that s0 and s1 are both weighted checksums using fibonacci weights +** in reverse order (the largest fibonacci weight occurs on the first element +** of the sequence being summed.) The s1 value spans all 32-bit +** terms of the sequence whereas s0 omits the final term. +** +** On a checkpoint, the WAL is first VFS.xSync-ed, then valid content of the +** WAL is transferred into the database, then the database is VFS.xSync-ed. +** The VFS.xSync operations serve as write barriers - all writes launched +** before the xSync must complete before any write that launches after the +** xSync begins. +** +** After each checkpoint, the salt-1 value is incremented and the salt-2 +** value is randomized. This prevents old and new frames in the WAL from +** being considered valid at the same time and being checkpointing together +** following a crash. +** +** READER ALGORITHM +** +** To read a page from the database (call it page number P), a reader +** first checks the WAL to see if it contains page P. If so, then the +** last valid instance of page P that is a followed by a commit frame +** or is a commit frame itself becomes the value read. If the WAL +** contains no copies of page P that are valid and which are a commit +** frame or are followed by a commit frame, then page P is read from +** the database file. +** +** To start a read transaction, the reader records the index of the last +** valid frame in the WAL. The reader uses this recorded "mxFrame" value +** for all subsequent read operations. New transactions can be appended +** to the WAL, but as long as the reader uses its original mxFrame value +** and ignores the newly appended content, it will see a consistent snapshot +** of the database from a single point in time. This technique allows +** multiple concurrent readers to view different versions of the database +** content simultaneously. +** +** The reader algorithm in the previous paragraphs works correctly, but +** because frames for page P can appear anywhere within the WAL, the +** reader has to scan the entire WAL looking for page P frames. If the +** WAL is large (multiple megabytes is typical) that scan can be slow, +** and read performance suffers. To overcome this problem, a separate +** data structure called the wal-index is maintained to expedite the +** search for frames of a particular page. +** +** WAL-INDEX FORMAT +** +** Conceptually, the wal-index is shared memory, though VFS implementations +** might choose to implement the wal-index using a mmapped file. Because +** the wal-index is shared memory, SQLite does not support journal_mode=WAL +** on a network filesystem. All users of the database must be able to +** share memory. +** +** In the default unix and windows implementation, the wal-index is a mmapped +** file whose name is the database name with a "-shm" suffix added. For that +** reason, the wal-index is sometimes called the "shm" file. +** +** The wal-index is transient. After a crash, the wal-index can (and should +** be) reconstructed from the original WAL file. In fact, the VFS is required +** to either truncate or zero the header of the wal-index when the last +** connection to it closes. Because the wal-index is transient, it can +** use an architecture-specific format; it does not have to be cross-platform. +** Hence, unlike the database and WAL file formats which store all values +** as big endian, the wal-index can store multi-byte values in the native +** byte order of the host computer. +** +** The purpose of the wal-index is to answer this question quickly: Given +** a page number P and a maximum frame index M, return the index of the +** last frame in the wal before frame M for page P in the WAL, or return +** NULL if there are no frames for page P in the WAL prior to M. +** +** The wal-index consists of a header region, followed by an one or +** more index blocks. +** +** The wal-index header contains the total number of frames within the WAL +** in the mxFrame field. +** +** Each index block except for the first contains information on +** HASHTABLE_NPAGE frames. The first index block contains information on +** HASHTABLE_NPAGE_ONE frames. The values of HASHTABLE_NPAGE_ONE and +** HASHTABLE_NPAGE are selected so that together the wal-index header and +** first index block are the same size as all other index blocks in the +** wal-index. The values are: +** +** HASHTABLE_NPAGE 4096 +** HASHTABLE_NPAGE_ONE 4062 +** +** Each index block contains two sections, a page-mapping that contains the +** database page number associated with each wal frame, and a hash-table +** that allows readers to query an index block for a specific page number. +** The page-mapping is an array of HASHTABLE_NPAGE (or HASHTABLE_NPAGE_ONE +** for the first index block) 32-bit page numbers. The first entry in the +** first index-block contains the database page number corresponding to the +** first frame in the WAL file. The first entry in the second index block +** in the WAL file corresponds to the (HASHTABLE_NPAGE_ONE+1)th frame in +** the log, and so on. +** +** The last index block in a wal-index usually contains less than the full +** complement of HASHTABLE_NPAGE (or HASHTABLE_NPAGE_ONE) page-numbers, +** depending on the contents of the WAL file. This does not change the +** allocated size of the page-mapping array - the page-mapping array merely +** contains unused entries. +** +** Even without using the hash table, the last frame for page P +** can be found by scanning the page-mapping sections of each index block +** starting with the last index block and moving toward the first, and +** within each index block, starting at the end and moving toward the +** beginning. The first entry that equals P corresponds to the frame +** holding the content for that page. +** +** The hash table consists of HASHTABLE_NSLOT 16-bit unsigned integers. +** HASHTABLE_NSLOT = 2*HASHTABLE_NPAGE, and there is one entry in the +** hash table for each page number in the mapping section, so the hash +** table is never more than half full. The expected number of collisions +** prior to finding a match is 1. Each entry of the hash table is an +** 1-based index of an entry in the mapping section of the same +** index block. Let K be the 1-based index of the largest entry in +** the mapping section. (For index blocks other than the last, K will +** always be exactly HASHTABLE_NPAGE (4096) and for the last index block +** K will be (mxFrame%HASHTABLE_NPAGE).) Unused slots of the hash table +** contain a value of 0. +** +** To look for page P in the hash table, first compute a hash iKey on +** P as follows: +** +** iKey = (P * 383) % HASHTABLE_NSLOT +** +** Then start scanning entries of the hash table, starting with iKey +** (wrapping around to the beginning when the end of the hash table is +** reached) until an unused hash slot is found. Let the first unused slot +** be at index iUnused. (iUnused might be less than iKey if there was +** wrap-around.) Because the hash table is never more than half full, +** the search is guaranteed to eventually hit an unused entry. Let +** iMax be the value between iKey and iUnused, closest to iUnused, +** where aHash[iMax]==P. If there is no iMax entry (if there exists +** no hash slot such that aHash[i]==p) then page P is not in the +** current index block. Otherwise the iMax-th mapping entry of the +** current index block corresponds to the last entry that references +** page P. +** +** A hash search begins with the last index block and moves toward the +** first index block, looking for entries corresponding to page P. On +** average, only two or three slots in each index block need to be +** examined in order to either find the last entry for page P, or to +** establish that no such entry exists in the block. Each index block +** holds over 4000 entries. So two or three index blocks are sufficient +** to cover a typical 10 megabyte WAL file, assuming 1K pages. 8 or 10 +** comparisons (on average) suffice to either locate a frame in the +** WAL or to establish that the frame does not exist in the WAL. This +** is much faster than scanning the entire 10MB WAL. +** +** Note that entries are added in order of increasing K. Hence, one +** reader might be using some value K0 and a second reader that started +** at a later time (after additional transactions were added to the WAL +** and to the wal-index) might be using a different value K1, where K1>K0. +** Both readers can use the same hash table and mapping section to get +** the correct result. There may be entries in the hash table with +** K>K0 but to the first reader, those entries will appear to be unused +** slots in the hash table and so the first reader will get an answer as +** if no values greater than K0 had ever been inserted into the hash table +** in the first place - which is what reader one wants. Meanwhile, the +** second reader using K1 will see additional values that were inserted +** later, which is exactly what reader two wants. +** +** When a rollback occurs, the value of K is decreased. Hash table entries +** that correspond to frames greater than the new K value are removed +** from the hash table at this point. +*/ +#ifndef SQLITE_OMIT_WAL + +#include "wal.h" + +/* +** Trace output macros +*/ +#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG) +int sqlite3WalTrace = 0; +# define WALTRACE(X) if(sqlite3WalTrace) sqlite3DebugPrintf X +#else +# define WALTRACE(X) +#endif + +/* +** The maximum (and only) versions of the wal and wal-index formats +** that may be interpreted by this version of SQLite. +** +** If a client begins recovering a WAL file and finds that (a) the checksum +** values in the wal-header are correct and (b) the version field is not +** WAL_MAX_VERSION, recovery fails and SQLite returns SQLITE_CANTOPEN. +** +** Similarly, if a client successfully reads a wal-index header (i.e. the +** checksum test is successful) and finds that the version field is not +** WALINDEX_MAX_VERSION, then no read-transaction is opened and SQLite +** returns SQLITE_CANTOPEN. +*/ +#define WAL_MAX_VERSION 3007000 +#define WALINDEX_MAX_VERSION 3007000 + +/* +** Index numbers for various locking bytes. WAL_NREADER is the number +** of available reader locks and should be at least 3. The default +** is SQLITE_SHM_NLOCK==8 and WAL_NREADER==5. +** +** Technically, the various VFSes are free to implement these locks however +** they see fit. However, compatibility is encouraged so that VFSes can +** interoperate. The standard implemention used on both unix and windows +** is for the index number to indicate a byte offset into the +** WalCkptInfo.aLock[] array in the wal-index header. In other words, all +** locks are on the shm file. The WALINDEX_LOCK_OFFSET constant (which +** should be 120) is the location in the shm file for the first locking +** byte. +*/ +#define WAL_WRITE_LOCK 0 +#define WAL_ALL_BUT_WRITE 1 +#define WAL_CKPT_LOCK 1 +#define WAL_RECOVER_LOCK 2 +#define WAL_READ_LOCK(I) (3+(I)) +#define WAL_NREADER (SQLITE_SHM_NLOCK-3) + + +/* Object declarations */ +typedef struct WalIndexHdr WalIndexHdr; +typedef struct WalIterator WalIterator; +typedef struct WalCkptInfo WalCkptInfo; + + +/* +** The following object holds a copy of the wal-index header content. +** +** The actual header in the wal-index consists of two copies of this +** object followed by one instance of the WalCkptInfo object. +** For all versions of SQLite through 3.10.0 and probably beyond, +** the locking bytes (WalCkptInfo.aLock) start at offset 120 and +** the total header size is 136 bytes. +** +** The szPage value can be any power of 2 between 512 and 32768, inclusive. +** Or it can be 1 to represent a 65536-byte page. The latter case was +** added in 3.7.1 when support for 64K pages was added. +*/ +struct WalIndexHdr { + u32 iVersion; /* Wal-index version */ + u32 unused; /* Unused (padding) field */ + u32 iChange; /* Counter incremented each transaction */ + u8 isInit; /* 1 when initialized */ + u8 bigEndCksum; /* True if checksums in WAL are big-endian */ + u16 szPage; /* Database page size in bytes. 1==64K */ + u32 mxFrame; /* Index of last valid frame in the WAL */ + u32 nPage; /* Size of database in pages */ + u32 aFrameCksum[2]; /* Checksum of last frame in log */ + u32 aSalt[2]; /* Two salt values copied from WAL header */ + u32 aCksum[2]; /* Checksum over all prior fields */ +}; + +/* +** A copy of the following object occurs in the wal-index immediately +** following the second copy of the WalIndexHdr. This object stores +** information used by checkpoint. +** +** nBackfill is the number of frames in the WAL that have been written +** back into the database. (We call the act of moving content from WAL to +** database "backfilling".) The nBackfill number is never greater than +** WalIndexHdr.mxFrame. nBackfill can only be increased by threads +** holding the WAL_CKPT_LOCK lock (which includes a recovery thread). +** However, a WAL_WRITE_LOCK thread can move the value of nBackfill from +** mxFrame back to zero when the WAL is reset. +** +** nBackfillAttempted is the largest value of nBackfill that a checkpoint +** has attempted to achieve. Normally nBackfill==nBackfillAtempted, however +** the nBackfillAttempted is set before any backfilling is done and the +** nBackfill is only set after all backfilling completes. So if a checkpoint +** crashes, nBackfillAttempted might be larger than nBackfill. The +** WalIndexHdr.mxFrame must never be less than nBackfillAttempted. +** +** The aLock[] field is a set of bytes used for locking. These bytes should +** never be read or written. +** +** There is one entry in aReadMark[] for each reader lock. If a reader +** holds read-lock K, then the value in aReadMark[K] is no greater than +** the mxFrame for that reader. The value READMARK_NOT_USED (0xffffffff) +** for any aReadMark[] means that entry is unused. aReadMark[0] is +** a special case; its value is never used and it exists as a place-holder +** to avoid having to offset aReadMark[] indexs by one. Readers holding +** WAL_READ_LOCK(0) always ignore the entire WAL and read all content +** directly from the database. +** +** The value of aReadMark[K] may only be changed by a thread that +** is holding an exclusive lock on WAL_READ_LOCK(K). Thus, the value of +** aReadMark[K] cannot changed while there is a reader is using that mark +** since the reader will be holding a shared lock on WAL_READ_LOCK(K). +** +** The checkpointer may only transfer frames from WAL to database where +** the frame numbers are less than or equal to every aReadMark[] that is +** in use (that is, every aReadMark[j] for which there is a corresponding +** WAL_READ_LOCK(j)). New readers (usually) pick the aReadMark[] with the +** largest value and will increase an unused aReadMark[] to mxFrame if there +** is not already an aReadMark[] equal to mxFrame. The exception to the +** previous sentence is when nBackfill equals mxFrame (meaning that everything +** in the WAL has been backfilled into the database) then new readers +** will choose aReadMark[0] which has value 0 and hence such reader will +** get all their all content directly from the database file and ignore +** the WAL. +** +** Writers normally append new frames to the end of the WAL. However, +** if nBackfill equals mxFrame (meaning that all WAL content has been +** written back into the database) and if no readers are using the WAL +** (in other words, if there are no WAL_READ_LOCK(i) where i>0) then +** the writer will first "reset" the WAL back to the beginning and start +** writing new content beginning at frame 1. +** +** We assume that 32-bit loads are atomic and so no locks are needed in +** order to read from any aReadMark[] entries. +*/ +struct WalCkptInfo { + u32 nBackfill; /* Number of WAL frames backfilled into DB */ + u32 aReadMark[WAL_NREADER]; /* Reader marks */ + u8 aLock[SQLITE_SHM_NLOCK]; /* Reserved space for locks */ + u32 nBackfillAttempted; /* WAL frames perhaps written, or maybe not */ + u32 notUsed0; /* Available for future enhancements */ +}; +#define READMARK_NOT_USED 0xffffffff + +/* +** This is a schematic view of the complete 136-byte header of the +** wal-index file (also known as the -shm file): +** +** +-----------------------------+ +** 0: | iVersion | \ +** +-----------------------------+ | +** 4: | (unused padding) | | +** +-----------------------------+ | +** 8: | iChange | | +** +-------+-------+-------------+ | +** 12: | bInit | bBig | szPage | | +** +-------+-------+-------------+ | +** 16: | mxFrame | | First copy of the +** +-----------------------------+ | WalIndexHdr object +** 20: | nPage | | +** +-----------------------------+ | +** 24: | aFrameCksum | | +** | | | +** +-----------------------------+ | +** 32: | aSalt | | +** | | | +** +-----------------------------+ | +** 40: | aCksum | | +** | | / +** +-----------------------------+ +** 48: | iVersion | \ +** +-----------------------------+ | +** 52: | (unused padding) | | +** +-----------------------------+ | +** 56: | iChange | | +** +-------+-------+-------------+ | +** 60: | bInit | bBig | szPage | | +** +-------+-------+-------------+ | Second copy of the +** 64: | mxFrame | | WalIndexHdr +** +-----------------------------+ | +** 68: | nPage | | +** +-----------------------------+ | +** 72: | aFrameCksum | | +** | | | +** +-----------------------------+ | +** 80: | aSalt | | +** | | | +** +-----------------------------+ | +** 88: | aCksum | | +** | | / +** +-----------------------------+ +** 96: | nBackfill | +** +-----------------------------+ +** 100: | 5 read marks | +** | | +** | | +** | | +** | | +** +-------+-------+------+------+ +** 120: | Write | Ckpt | Rcvr | Rd0 | \ +** +-------+-------+------+------+ ) 8 lock bytes +** | Read1 | Read2 | Rd3 | Rd4 | / +** +-------+-------+------+------+ +** 128: | nBackfillAttempted | +** +-----------------------------+ +** 132: | (unused padding) | +** +-----------------------------+ +*/ + +/* A block of WALINDEX_LOCK_RESERVED bytes beginning at +** WALINDEX_LOCK_OFFSET is reserved for locks. Since some systems +** only support mandatory file-locks, we do not read or write data +** from the region of the file on which locks are applied. +*/ +#define WALINDEX_LOCK_OFFSET (sizeof(WalIndexHdr)*2+offsetof(WalCkptInfo,aLock)) +#define WALINDEX_HDR_SIZE (sizeof(WalIndexHdr)*2+sizeof(WalCkptInfo)) + +/* Size of header before each frame in wal */ +#define WAL_FRAME_HDRSIZE 24 + +/* Size of write ahead log header, including checksum. */ +#define WAL_HDRSIZE 32 + +/* WAL magic value. Either this value, or the same value with the least +** significant bit also set (WAL_MAGIC | 0x00000001) is stored in 32-bit +** big-endian format in the first 4 bytes of a WAL file. +** +** If the LSB is set, then the checksums for each frame within the WAL +** file are calculated by treating all data as an array of 32-bit +** big-endian words. Otherwise, they are calculated by interpreting +** all data as 32-bit little-endian words. +*/ +#define WAL_MAGIC 0x377f0682 + +/* +** Return the offset of frame iFrame in the write-ahead log file, +** assuming a database page size of szPage bytes. The offset returned +** is to the start of the write-ahead log frame-header. +*/ +#define walFrameOffset(iFrame, szPage) ( \ + WAL_HDRSIZE + ((iFrame)-1)*(i64)((szPage)+WAL_FRAME_HDRSIZE) \ +) + +/* +** An open write-ahead log file is represented by an instance of the +** following object. +*/ +struct Wal { + sqlite3_vfs *pVfs; /* The VFS used to create pDbFd */ + sqlite3_file *pDbFd; /* File handle for the database file */ + sqlite3_file *pWalFd; /* File handle for WAL file */ + u32 iCallback; /* Value to pass to log callback (or 0) */ + i64 mxWalSize; /* Truncate WAL to this size upon reset */ + int nWiData; /* Size of array apWiData */ + int szFirstBlock; /* Size of first block written to WAL file */ + volatile u32 **apWiData; /* Pointer to wal-index content in memory */ + u32 szPage; /* Database page size */ + i16 readLock; /* Which read lock is being held. -1 for none */ + u8 syncFlags; /* Flags to use to sync header writes */ + u8 exclusiveMode; /* Non-zero if connection is in exclusive mode */ + u8 writeLock; /* True if in a write transaction */ + u8 ckptLock; /* True if holding a checkpoint lock */ + u8 readOnly; /* WAL_RDWR, WAL_RDONLY, or WAL_SHM_RDONLY */ + u8 truncateOnCommit; /* True to truncate WAL file on commit */ + u8 syncHeader; /* Fsync the WAL header if true */ + u8 padToSectorBoundary; /* Pad transactions out to the next sector */ + u8 bShmUnreliable; /* SHM content is read-only and unreliable */ + WalIndexHdr hdr; /* Wal-index header for current transaction */ + u32 minFrame; /* Ignore wal frames before this one */ + u32 iReCksum; /* On commit, recalculate checksums from here */ + const char *zWalName; /* Name of WAL file */ + u32 nCkpt; /* Checkpoint sequence counter in the wal-header */ +#ifdef SQLITE_DEBUG + u8 lockError; /* True if a locking error has occurred */ +#endif +#ifdef SQLITE_ENABLE_SNAPSHOT + WalIndexHdr *pSnapshot; /* Start transaction here if not NULL */ +#endif +#ifdef SQLITE_ENABLE_SETLK_TIMEOUT + sqlite3 *db; +#endif +}; + +/* +** Candidate values for Wal.exclusiveMode. +*/ +#define WAL_NORMAL_MODE 0 +#define WAL_EXCLUSIVE_MODE 1 +#define WAL_HEAPMEMORY_MODE 2 + +/* +** Possible values for WAL.readOnly +*/ +#define WAL_RDWR 0 /* Normal read/write connection */ +#define WAL_RDONLY 1 /* The WAL file is readonly */ +#define WAL_SHM_RDONLY 2 /* The SHM file is readonly */ + +/* +** Each page of the wal-index mapping contains a hash-table made up of +** an array of HASHTABLE_NSLOT elements of the following type. +*/ +typedef u16 ht_slot; + +/* +** This structure is used to implement an iterator that loops through +** all frames in the WAL in database page order. Where two or more frames +** correspond to the same database page, the iterator visits only the +** frame most recently written to the WAL (in other words, the frame with +** the largest index). +** +** The internals of this structure are only accessed by: +** +** walIteratorInit() - Create a new iterator, +** walIteratorNext() - Step an iterator, +** walIteratorFree() - Free an iterator. +** +** This functionality is used by the checkpoint code (see walCheckpoint()). +*/ +struct WalIterator { + u32 iPrior; /* Last result returned from the iterator */ + int nSegment; /* Number of entries in aSegment[] */ + struct WalSegment { + int iNext; /* Next slot in aIndex[] not yet returned */ + ht_slot *aIndex; /* i0, i1, i2... such that aPgno[iN] ascend */ + u32 *aPgno; /* Array of page numbers. */ + int nEntry; /* Nr. of entries in aPgno[] and aIndex[] */ + int iZero; /* Frame number associated with aPgno[0] */ + } aSegment[1]; /* One for every 32KB page in the wal-index */ +}; + +/* +** Define the parameters of the hash tables in the wal-index file. There +** is a hash-table following every HASHTABLE_NPAGE page numbers in the +** wal-index. +** +** Changing any of these constants will alter the wal-index format and +** create incompatibilities. +*/ +#define HASHTABLE_NPAGE 4096 /* Must be power of 2 */ +#define HASHTABLE_HASH_1 383 /* Should be prime */ +#define HASHTABLE_NSLOT (HASHTABLE_NPAGE*2) /* Must be a power of 2 */ + +/* +** The block of page numbers associated with the first hash-table in a +** wal-index is smaller than usual. This is so that there is a complete +** hash-table on each aligned 32KB page of the wal-index. +*/ +#define HASHTABLE_NPAGE_ONE (HASHTABLE_NPAGE - (WALINDEX_HDR_SIZE/sizeof(u32))) + +/* The wal-index is divided into pages of WALINDEX_PGSZ bytes each. */ +#define WALINDEX_PGSZ ( \ + sizeof(ht_slot)*HASHTABLE_NSLOT + HASHTABLE_NPAGE*sizeof(u32) \ +) + +/* +** Obtain a pointer to the iPage'th page of the wal-index. The wal-index +** is broken into pages of WALINDEX_PGSZ bytes. Wal-index pages are +** numbered from zero. +** +** If the wal-index is currently smaller the iPage pages then the size +** of the wal-index might be increased, but only if it is safe to do +** so. It is safe to enlarge the wal-index if pWal->writeLock is true +** or pWal->exclusiveMode==WAL_HEAPMEMORY_MODE. +** +** Three possible result scenarios: +** +** (1) rc==SQLITE_OK and *ppPage==Requested-Wal-Index-Page +** (2) rc>=SQLITE_ERROR and *ppPage==NULL +** (3) rc==SQLITE_OK and *ppPage==NULL // only if iPage==0 +** +** Scenario (3) can only occur when pWal->writeLock is false and iPage==0 +*/ +static SQLITE_NOINLINE int walIndexPageRealloc( + Wal *pWal, /* The WAL context */ + int iPage, /* The page we seek */ + volatile u32 **ppPage /* Write the page pointer here */ +){ + int rc = SQLITE_OK; + + /* Enlarge the pWal->apWiData[] array if required */ + if( pWal->nWiData<=iPage ){ + sqlite3_int64 nByte = sizeof(u32*)*(iPage+1); + volatile u32 **apNew; + apNew = (volatile u32 **)sqlite3Realloc((void *)pWal->apWiData, nByte); + if( !apNew ){ + *ppPage = 0; + return SQLITE_NOMEM_BKPT; + } + memset((void*)&apNew[pWal->nWiData], 0, + sizeof(u32*)*(iPage+1-pWal->nWiData)); + pWal->apWiData = apNew; + pWal->nWiData = iPage+1; + } + + /* Request a pointer to the required page from the VFS */ + assert( pWal->apWiData[iPage]==0 ); + if( pWal->exclusiveMode==WAL_HEAPMEMORY_MODE ){ + pWal->apWiData[iPage] = (u32 volatile *)sqlite3MallocZero(WALINDEX_PGSZ); + if( !pWal->apWiData[iPage] ) rc = SQLITE_NOMEM_BKPT; + }else{ + rc = sqlite3OsShmMap(pWal->pDbFd, iPage, WALINDEX_PGSZ, + pWal->writeLock, (void volatile **)&pWal->apWiData[iPage] + ); + assert( pWal->apWiData[iPage]!=0 + || rc!=SQLITE_OK + || (pWal->writeLock==0 && iPage==0) ); + testcase( pWal->apWiData[iPage]==0 && rc==SQLITE_OK ); + if( rc==SQLITE_OK ){ + if( iPage>0 && sqlite3FaultSim(600) ) rc = SQLITE_NOMEM; + }else if( (rc&0xff)==SQLITE_READONLY ){ + pWal->readOnly |= WAL_SHM_RDONLY; + if( rc==SQLITE_READONLY ){ + rc = SQLITE_OK; + } + } + } + + *ppPage = pWal->apWiData[iPage]; + assert( iPage==0 || *ppPage || rc!=SQLITE_OK ); + return rc; +} +static int walIndexPage( + Wal *pWal, /* The WAL context */ + int iPage, /* The page we seek */ + volatile u32 **ppPage /* Write the page pointer here */ +){ + if( pWal->nWiData<=iPage || (*ppPage = pWal->apWiData[iPage])==0 ){ + return walIndexPageRealloc(pWal, iPage, ppPage); + } + return SQLITE_OK; +} + +/* +** Return a pointer to the WalCkptInfo structure in the wal-index. +*/ +static volatile WalCkptInfo *walCkptInfo(Wal *pWal){ + assert( pWal->nWiData>0 && pWal->apWiData[0] ); + return (volatile WalCkptInfo*)&(pWal->apWiData[0][sizeof(WalIndexHdr)/2]); +} + +/* +** Return a pointer to the WalIndexHdr structure in the wal-index. +*/ +static volatile WalIndexHdr *walIndexHdr(Wal *pWal){ + assert( pWal->nWiData>0 && pWal->apWiData[0] ); + return (volatile WalIndexHdr*)pWal->apWiData[0]; +} + +/* +** The argument to this macro must be of type u32. On a little-endian +** architecture, it returns the u32 value that results from interpreting +** the 4 bytes as a big-endian value. On a big-endian architecture, it +** returns the value that would be produced by interpreting the 4 bytes +** of the input value as a little-endian integer. +*/ +#define BYTESWAP32(x) ( \ + (((x)&0x000000FF)<<24) + (((x)&0x0000FF00)<<8) \ + + (((x)&0x00FF0000)>>8) + (((x)&0xFF000000)>>24) \ +) + +/* +** Generate or extend an 8 byte checksum based on the data in +** array aByte[] and the initial values of aIn[0] and aIn[1] (or +** initial values of 0 and 0 if aIn==NULL). +** +** The checksum is written back into aOut[] before returning. +** +** nByte must be a positive multiple of 8. +*/ +static void walChecksumBytes( + int nativeCksum, /* True for native byte-order, false for non-native */ + u8 *a, /* Content to be checksummed */ + int nByte, /* Bytes of content in a[]. Must be a multiple of 8. */ + const u32 *aIn, /* Initial checksum value input */ + u32 *aOut /* OUT: Final checksum value output */ +){ + u32 s1, s2; + u32 *aData = (u32 *)a; + u32 *aEnd = (u32 *)&a[nByte]; + + if( aIn ){ + s1 = aIn[0]; + s2 = aIn[1]; + }else{ + s1 = s2 = 0; + } + + assert( nByte>=8 ); + assert( (nByte&0x00000007)==0 ); + assert( nByte<=65536 ); + + if( nativeCksum ){ + do { + s1 += *aData++ + s2; + s2 += *aData++ + s1; + }while( aData<aEnd ); + }else{ + do { + s1 += BYTESWAP32(aData[0]) + s2; + s2 += BYTESWAP32(aData[1]) + s1; + aData += 2; + }while( aData<aEnd ); + } + + aOut[0] = s1; + aOut[1] = s2; +} + +/* +** If there is the possibility of concurrent access to the SHM file +** from multiple threads and/or processes, then do a memory barrier. +*/ +static void walShmBarrier(Wal *pWal){ + if( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE ){ + sqlite3OsShmBarrier(pWal->pDbFd); + } +} + +/* +** Add the SQLITE_NO_TSAN as part of the return-type of a function +** definition as a hint that the function contains constructs that +** might give false-positive TSAN warnings. +** +** See tag-20200519-1. +*/ +#if defined(__clang__) && !defined(SQLITE_NO_TSAN) +# define SQLITE_NO_TSAN __attribute__((no_sanitize_thread)) +#else +# define SQLITE_NO_TSAN +#endif + +/* +** Write the header information in pWal->hdr into the wal-index. +** +** The checksum on pWal->hdr is updated before it is written. +*/ +static SQLITE_NO_TSAN void walIndexWriteHdr(Wal *pWal){ + volatile WalIndexHdr *aHdr = walIndexHdr(pWal); + const int nCksum = offsetof(WalIndexHdr, aCksum); + + assert( pWal->writeLock ); + pWal->hdr.isInit = 1; + pWal->hdr.iVersion = WALINDEX_MAX_VERSION; + walChecksumBytes(1, (u8*)&pWal->hdr, nCksum, 0, pWal->hdr.aCksum); + /* Possible TSAN false-positive. See tag-20200519-1 */ + memcpy((void*)&aHdr[1], (const void*)&pWal->hdr, sizeof(WalIndexHdr)); + walShmBarrier(pWal); + memcpy((void*)&aHdr[0], (const void*)&pWal->hdr, sizeof(WalIndexHdr)); +} + +/* +** This function encodes a single frame header and writes it to a buffer +** supplied by the caller. A frame-header is made up of a series of +** 4-byte big-endian integers, as follows: +** +** 0: Page number. +** 4: For commit records, the size of the database image in pages +** after the commit. For all other records, zero. +** 8: Salt-1 (copied from the wal-header) +** 12: Salt-2 (copied from the wal-header) +** 16: Checksum-1. +** 20: Checksum-2. +*/ +static void walEncodeFrame( + Wal *pWal, /* The write-ahead log */ + u32 iPage, /* Database page number for frame */ + u32 nTruncate, /* New db size (or 0 for non-commit frames) */ + u8 *aData, /* Pointer to page data */ + u8 *aFrame /* OUT: Write encoded frame here */ +){ + int nativeCksum; /* True for native byte-order checksums */ + u32 *aCksum = pWal->hdr.aFrameCksum; + assert( WAL_FRAME_HDRSIZE==24 ); + sqlite3Put4byte(&aFrame[0], iPage); + sqlite3Put4byte(&aFrame[4], nTruncate); + if( pWal->iReCksum==0 ){ + memcpy(&aFrame[8], pWal->hdr.aSalt, 8); + + nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN); + walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum); + walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum); + + sqlite3Put4byte(&aFrame[16], aCksum[0]); + sqlite3Put4byte(&aFrame[20], aCksum[1]); + }else{ + memset(&aFrame[8], 0, 16); + } +} + +/* +** Check to see if the frame with header in aFrame[] and content +** in aData[] is valid. If it is a valid frame, fill *piPage and +** *pnTruncate and return true. Return if the frame is not valid. +*/ +static int walDecodeFrame( + Wal *pWal, /* The write-ahead log */ + u32 *piPage, /* OUT: Database page number for frame */ + u32 *pnTruncate, /* OUT: New db size (or 0 if not commit) */ + u8 *aData, /* Pointer to page data (for checksum) */ + u8 *aFrame /* Frame data */ +){ + int nativeCksum; /* True for native byte-order checksums */ + u32 *aCksum = pWal->hdr.aFrameCksum; + u32 pgno; /* Page number of the frame */ + assert( WAL_FRAME_HDRSIZE==24 ); + + /* A frame is only valid if the salt values in the frame-header + ** match the salt values in the wal-header. + */ + if( memcmp(&pWal->hdr.aSalt, &aFrame[8], 8)!=0 ){ + return 0; + } + + /* A frame is only valid if the page number is creater than zero. + */ + pgno = sqlite3Get4byte(&aFrame[0]); + if( pgno==0 ){ + return 0; + } + + /* A frame is only valid if a checksum of the WAL header, + ** all prior frams, the first 16 bytes of this frame-header, + ** and the frame-data matches the checksum in the last 8 + ** bytes of this frame-header. + */ + nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN); + walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum); + walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum); + if( aCksum[0]!=sqlite3Get4byte(&aFrame[16]) + || aCksum[1]!=sqlite3Get4byte(&aFrame[20]) + ){ + /* Checksum failed. */ + return 0; + } + + /* If we reach this point, the frame is valid. Return the page number + ** and the new database size. + */ + *piPage = pgno; + *pnTruncate = sqlite3Get4byte(&aFrame[4]); + return 1; +} + + +#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG) +/* +** Names of locks. This routine is used to provide debugging output and is not +** a part of an ordinary build. +*/ +static const char *walLockName(int lockIdx){ + if( lockIdx==WAL_WRITE_LOCK ){ + return "WRITE-LOCK"; + }else if( lockIdx==WAL_CKPT_LOCK ){ + return "CKPT-LOCK"; + }else if( lockIdx==WAL_RECOVER_LOCK ){ + return "RECOVER-LOCK"; + }else{ + static char zName[15]; + sqlite3_snprintf(sizeof(zName), zName, "READ-LOCK[%d]", + lockIdx-WAL_READ_LOCK(0)); + return zName; + } +} +#endif /*defined(SQLITE_TEST) || defined(SQLITE_DEBUG) */ + + +/* +** Set or release locks on the WAL. Locks are either shared or exclusive. +** A lock cannot be moved directly between shared and exclusive - it must go +** through the unlocked state first. +** +** In locking_mode=EXCLUSIVE, all of these routines become no-ops. +*/ +static int walLockShared(Wal *pWal, int lockIdx){ + int rc; + if( pWal->exclusiveMode ) return SQLITE_OK; + rc = sqlite3OsShmLock(pWal->pDbFd, lockIdx, 1, + SQLITE_SHM_LOCK | SQLITE_SHM_SHARED); + WALTRACE(("WAL%p: acquire SHARED-%s %s\n", pWal, + walLockName(lockIdx), rc ? "failed" : "ok")); + VVA_ONLY( pWal->lockError = (u8)(rc!=SQLITE_OK && (rc&0xFF)!=SQLITE_BUSY); ) + return rc; +} +static void walUnlockShared(Wal *pWal, int lockIdx){ + if( pWal->exclusiveMode ) return; + (void)sqlite3OsShmLock(pWal->pDbFd, lockIdx, 1, + SQLITE_SHM_UNLOCK | SQLITE_SHM_SHARED); + WALTRACE(("WAL%p: release SHARED-%s\n", pWal, walLockName(lockIdx))); +} +static int walLockExclusive(Wal *pWal, int lockIdx, int n){ + int rc; + if( pWal->exclusiveMode ) return SQLITE_OK; + rc = sqlite3OsShmLock(pWal->pDbFd, lockIdx, n, + SQLITE_SHM_LOCK | SQLITE_SHM_EXCLUSIVE); + WALTRACE(("WAL%p: acquire EXCLUSIVE-%s cnt=%d %s\n", pWal, + walLockName(lockIdx), n, rc ? "failed" : "ok")); + VVA_ONLY( pWal->lockError = (u8)(rc!=SQLITE_OK && (rc&0xFF)!=SQLITE_BUSY); ) + return rc; +} +static void walUnlockExclusive(Wal *pWal, int lockIdx, int n){ + if( pWal->exclusiveMode ) return; + (void)sqlite3OsShmLock(pWal->pDbFd, lockIdx, n, + SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE); + WALTRACE(("WAL%p: release EXCLUSIVE-%s cnt=%d\n", pWal, + walLockName(lockIdx), n)); +} + +/* +** Compute a hash on a page number. The resulting hash value must land +** between 0 and (HASHTABLE_NSLOT-1). The walHashNext() function advances +** the hash to the next value in the event of a collision. +*/ +static int walHash(u32 iPage){ + assert( iPage>0 ); + assert( (HASHTABLE_NSLOT & (HASHTABLE_NSLOT-1))==0 ); + return (iPage*HASHTABLE_HASH_1) & (HASHTABLE_NSLOT-1); +} +static int walNextHash(int iPriorHash){ + return (iPriorHash+1)&(HASHTABLE_NSLOT-1); +} + +/* +** An instance of the WalHashLoc object is used to describe the location +** of a page hash table in the wal-index. This becomes the return value +** from walHashGet(). +*/ +typedef struct WalHashLoc WalHashLoc; +struct WalHashLoc { + volatile ht_slot *aHash; /* Start of the wal-index hash table */ + volatile u32 *aPgno; /* aPgno[1] is the page of first frame indexed */ + u32 iZero; /* One less than the frame number of first indexed*/ +}; + +/* +** Return pointers to the hash table and page number array stored on +** page iHash of the wal-index. The wal-index is broken into 32KB pages +** numbered starting from 0. +** +** Set output variable pLoc->aHash to point to the start of the hash table +** in the wal-index file. Set pLoc->iZero to one less than the frame +** number of the first frame indexed by this hash table. If a +** slot in the hash table is set to N, it refers to frame number +** (pLoc->iZero+N) in the log. +** +** Finally, set pLoc->aPgno so that pLoc->aPgno[0] is the page number of the +** first frame indexed by the hash table, frame (pLoc->iZero). +*/ +static int walHashGet( + Wal *pWal, /* WAL handle */ + int iHash, /* Find the iHash'th table */ + WalHashLoc *pLoc /* OUT: Hash table location */ +){ + int rc; /* Return code */ + + rc = walIndexPage(pWal, iHash, &pLoc->aPgno); + assert( rc==SQLITE_OK || iHash>0 ); + + if( pLoc->aPgno ){ + pLoc->aHash = (volatile ht_slot *)&pLoc->aPgno[HASHTABLE_NPAGE]; + if( iHash==0 ){ + pLoc->aPgno = &pLoc->aPgno[WALINDEX_HDR_SIZE/sizeof(u32)]; + pLoc->iZero = 0; + }else{ + pLoc->iZero = HASHTABLE_NPAGE_ONE + (iHash-1)*HASHTABLE_NPAGE; + } + }else if( NEVER(rc==SQLITE_OK) ){ + rc = SQLITE_ERROR; + } + return rc; +} + +/* +** Return the number of the wal-index page that contains the hash-table +** and page-number array that contain entries corresponding to WAL frame +** iFrame. The wal-index is broken up into 32KB pages. Wal-index pages +** are numbered starting from 0. +*/ +static int walFramePage(u32 iFrame){ + int iHash = (iFrame+HASHTABLE_NPAGE-HASHTABLE_NPAGE_ONE-1) / HASHTABLE_NPAGE; + assert( (iHash==0 || iFrame>HASHTABLE_NPAGE_ONE) + && (iHash>=1 || iFrame<=HASHTABLE_NPAGE_ONE) + && (iHash<=1 || iFrame>(HASHTABLE_NPAGE_ONE+HASHTABLE_NPAGE)) + && (iHash>=2 || iFrame<=HASHTABLE_NPAGE_ONE+HASHTABLE_NPAGE) + && (iHash<=2 || iFrame>(HASHTABLE_NPAGE_ONE+2*HASHTABLE_NPAGE)) + ); + assert( iHash>=0 ); + return iHash; +} + +/* +** Return the page number associated with frame iFrame in this WAL. +*/ +static u32 walFramePgno(Wal *pWal, u32 iFrame){ + int iHash = walFramePage(iFrame); + if( iHash==0 ){ + return pWal->apWiData[0][WALINDEX_HDR_SIZE/sizeof(u32) + iFrame - 1]; + } + return pWal->apWiData[iHash][(iFrame-1-HASHTABLE_NPAGE_ONE)%HASHTABLE_NPAGE]; +} + +/* +** Remove entries from the hash table that point to WAL slots greater +** than pWal->hdr.mxFrame. +** +** This function is called whenever pWal->hdr.mxFrame is decreased due +** to a rollback or savepoint. +** +** At most only the hash table containing pWal->hdr.mxFrame needs to be +** updated. Any later hash tables will be automatically cleared when +** pWal->hdr.mxFrame advances to the point where those hash tables are +** actually needed. +*/ +static void walCleanupHash(Wal *pWal){ + WalHashLoc sLoc; /* Hash table location */ + int iLimit = 0; /* Zero values greater than this */ + int nByte; /* Number of bytes to zero in aPgno[] */ + int i; /* Used to iterate through aHash[] */ + + assert( pWal->writeLock ); + testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE-1 ); + testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE ); + testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE+1 ); + + if( pWal->hdr.mxFrame==0 ) return; + + /* Obtain pointers to the hash-table and page-number array containing + ** the entry that corresponds to frame pWal->hdr.mxFrame. It is guaranteed + ** that the page said hash-table and array reside on is already mapped.(1) + */ + assert( pWal->nWiData>walFramePage(pWal->hdr.mxFrame) ); + assert( pWal->apWiData[walFramePage(pWal->hdr.mxFrame)] ); + i = walHashGet(pWal, walFramePage(pWal->hdr.mxFrame), &sLoc); + if( NEVER(i) ) return; /* Defense-in-depth, in case (1) above is wrong */ + + /* Zero all hash-table entries that correspond to frame numbers greater + ** than pWal->hdr.mxFrame. + */ + iLimit = pWal->hdr.mxFrame - sLoc.iZero; + assert( iLimit>0 ); + for(i=0; i<HASHTABLE_NSLOT; i++){ + if( sLoc.aHash[i]>iLimit ){ + sLoc.aHash[i] = 0; + } + } + + /* Zero the entries in the aPgno array that correspond to frames with + ** frame numbers greater than pWal->hdr.mxFrame. + */ + nByte = (int)((char *)sLoc.aHash - (char *)&sLoc.aPgno[iLimit]); + assert( nByte>=0 ); + memset((void *)&sLoc.aPgno[iLimit], 0, nByte); + +#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT + /* Verify that the every entry in the mapping region is still reachable + ** via the hash table even after the cleanup. + */ + if( iLimit ){ + int j; /* Loop counter */ + int iKey; /* Hash key */ + for(j=0; j<iLimit; j++){ + for(iKey=walHash(sLoc.aPgno[j]);sLoc.aHash[iKey];iKey=walNextHash(iKey)){ + if( sLoc.aHash[iKey]==j+1 ) break; + } + assert( sLoc.aHash[iKey]==j+1 ); + } + } +#endif /* SQLITE_ENABLE_EXPENSIVE_ASSERT */ +} + + +/* +** Set an entry in the wal-index that will map database page number +** pPage into WAL frame iFrame. +*/ +static int walIndexAppend(Wal *pWal, u32 iFrame, u32 iPage){ + int rc; /* Return code */ + WalHashLoc sLoc; /* Wal-index hash table location */ + + rc = walHashGet(pWal, walFramePage(iFrame), &sLoc); + + /* Assuming the wal-index file was successfully mapped, populate the + ** page number array and hash table entry. + */ + if( rc==SQLITE_OK ){ + int iKey; /* Hash table key */ + int idx; /* Value to write to hash-table slot */ + int nCollide; /* Number of hash collisions */ + + idx = iFrame - sLoc.iZero; + assert( idx <= HASHTABLE_NSLOT/2 + 1 ); + + /* If this is the first entry to be added to this hash-table, zero the + ** entire hash table and aPgno[] array before proceeding. + */ + if( idx==1 ){ + int nByte = (int)((u8*)&sLoc.aHash[HASHTABLE_NSLOT] - (u8*)sLoc.aPgno); + assert( nByte>=0 ); + memset((void*)sLoc.aPgno, 0, nByte); + } + + /* If the entry in aPgno[] is already set, then the previous writer + ** must have exited unexpectedly in the middle of a transaction (after + ** writing one or more dirty pages to the WAL to free up memory). + ** Remove the remnants of that writers uncommitted transaction from + ** the hash-table before writing any new entries. + */ + if( sLoc.aPgno[idx-1] ){ + walCleanupHash(pWal); + assert( !sLoc.aPgno[idx-1] ); + } + + /* Write the aPgno[] array entry and the hash-table slot. */ + nCollide = idx; + for(iKey=walHash(iPage); sLoc.aHash[iKey]; iKey=walNextHash(iKey)){ + if( (nCollide--)==0 ) return SQLITE_CORRUPT_BKPT; + } + sLoc.aPgno[idx-1] = iPage; + AtomicStore(&sLoc.aHash[iKey], (ht_slot)idx); + +#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT + /* Verify that the number of entries in the hash table exactly equals + ** the number of entries in the mapping region. + */ + { + int i; /* Loop counter */ + int nEntry = 0; /* Number of entries in the hash table */ + for(i=0; i<HASHTABLE_NSLOT; i++){ if( sLoc.aHash[i] ) nEntry++; } + assert( nEntry==idx ); + } + + /* Verify that the every entry in the mapping region is reachable + ** via the hash table. This turns out to be a really, really expensive + ** thing to check, so only do this occasionally - not on every + ** iteration. + */ + if( (idx&0x3ff)==0 ){ + int i; /* Loop counter */ + for(i=0; i<idx; i++){ + for(iKey=walHash(sLoc.aPgno[i]); + sLoc.aHash[iKey]; + iKey=walNextHash(iKey)){ + if( sLoc.aHash[iKey]==i+1 ) break; + } + assert( sLoc.aHash[iKey]==i+1 ); + } + } +#endif /* SQLITE_ENABLE_EXPENSIVE_ASSERT */ + } + + return rc; +} + + +/* +** Recover the wal-index by reading the write-ahead log file. +** +** This routine first tries to establish an exclusive lock on the +** wal-index to prevent other threads/processes from doing anything +** with the WAL or wal-index while recovery is running. The +** WAL_RECOVER_LOCK is also held so that other threads will know +** that this thread is running recovery. If unable to establish +** the necessary locks, this routine returns SQLITE_BUSY. +*/ +static int walIndexRecover(Wal *pWal){ + int rc; /* Return Code */ + i64 nSize; /* Size of log file */ + u32 aFrameCksum[2] = {0, 0}; + int iLock; /* Lock offset to lock for checkpoint */ + + /* Obtain an exclusive lock on all byte in the locking range not already + ** locked by the caller. The caller is guaranteed to have locked the + ** WAL_WRITE_LOCK byte, and may have also locked the WAL_CKPT_LOCK byte. + ** If successful, the same bytes that are locked here are unlocked before + ** this function returns. + */ + assert( pWal->ckptLock==1 || pWal->ckptLock==0 ); + assert( WAL_ALL_BUT_WRITE==WAL_WRITE_LOCK+1 ); + assert( WAL_CKPT_LOCK==WAL_ALL_BUT_WRITE ); + assert( pWal->writeLock ); + iLock = WAL_ALL_BUT_WRITE + pWal->ckptLock; + rc = walLockExclusive(pWal, iLock, WAL_READ_LOCK(0)-iLock); + if( rc ){ + return rc; + } + + WALTRACE(("WAL%p: recovery begin...\n", pWal)); + + memset(&pWal->hdr, 0, sizeof(WalIndexHdr)); + + rc = sqlite3OsFileSize(pWal->pWalFd, &nSize); + if( rc!=SQLITE_OK ){ + goto recovery_error; + } + + if( nSize>WAL_HDRSIZE ){ + u8 aBuf[WAL_HDRSIZE]; /* Buffer to load WAL header into */ + u32 *aPrivate = 0; /* Heap copy of *-shm hash being populated */ + u8 *aFrame = 0; /* Malloc'd buffer to load entire frame */ + int szFrame; /* Number of bytes in buffer aFrame[] */ + u8 *aData; /* Pointer to data part of aFrame buffer */ + int szPage; /* Page size according to the log */ + u32 magic; /* Magic value read from WAL header */ + u32 version; /* Magic value read from WAL header */ + int isValid; /* True if this frame is valid */ + u32 iPg; /* Current 32KB wal-index page */ + u32 iLastFrame; /* Last frame in wal, based on nSize alone */ + + /* Read in the WAL header. */ + rc = sqlite3OsRead(pWal->pWalFd, aBuf, WAL_HDRSIZE, 0); + if( rc!=SQLITE_OK ){ + goto recovery_error; + } + + /* If the database page size is not a power of two, or is greater than + ** SQLITE_MAX_PAGE_SIZE, conclude that the WAL file contains no valid + ** data. Similarly, if the 'magic' value is invalid, ignore the whole + ** WAL file. + */ + magic = sqlite3Get4byte(&aBuf[0]); + szPage = sqlite3Get4byte(&aBuf[8]); + if( (magic&0xFFFFFFFE)!=WAL_MAGIC + || szPage&(szPage-1) + || szPage>SQLITE_MAX_PAGE_SIZE + || szPage<512 + ){ + goto finished; + } + pWal->hdr.bigEndCksum = (u8)(magic&0x00000001); + pWal->szPage = szPage; + pWal->nCkpt = sqlite3Get4byte(&aBuf[12]); + memcpy(&pWal->hdr.aSalt, &aBuf[16], 8); + + /* Verify that the WAL header checksum is correct */ + walChecksumBytes(pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN, + aBuf, WAL_HDRSIZE-2*4, 0, pWal->hdr.aFrameCksum + ); + if( pWal->hdr.aFrameCksum[0]!=sqlite3Get4byte(&aBuf[24]) + || pWal->hdr.aFrameCksum[1]!=sqlite3Get4byte(&aBuf[28]) + ){ + goto finished; + } + + /* Verify that the version number on the WAL format is one that + ** are able to understand */ + version = sqlite3Get4byte(&aBuf[4]); + if( version!=WAL_MAX_VERSION ){ + rc = SQLITE_CANTOPEN_BKPT; + goto finished; + } + + /* Malloc a buffer to read frames into. */ + szFrame = szPage + WAL_FRAME_HDRSIZE; + aFrame = (u8 *)sqlite3_malloc64(szFrame + WALINDEX_PGSZ); + if( !aFrame ){ + rc = SQLITE_NOMEM_BKPT; + goto recovery_error; + } + aData = &aFrame[WAL_FRAME_HDRSIZE]; + aPrivate = (u32*)&aData[szPage]; + + /* Read all frames from the log file. */ + iLastFrame = (nSize - WAL_HDRSIZE) / szFrame; + for(iPg=0; iPg<=(u32)walFramePage(iLastFrame); iPg++){ + u32 *aShare; + u32 iFrame; /* Index of last frame read */ + u32 iLast = MIN(iLastFrame, HASHTABLE_NPAGE_ONE+iPg*HASHTABLE_NPAGE); + u32 iFirst = 1 + (iPg==0?0:HASHTABLE_NPAGE_ONE+(iPg-1)*HASHTABLE_NPAGE); + u32 nHdr, nHdr32; + rc = walIndexPage(pWal, iPg, (volatile u32**)&aShare); + assert( aShare!=0 || rc!=SQLITE_OK ); + if( aShare==0 ) break; + pWal->apWiData[iPg] = aPrivate; + + for(iFrame=iFirst; iFrame<=iLast; iFrame++){ + i64 iOffset = walFrameOffset(iFrame, szPage); + u32 pgno; /* Database page number for frame */ + u32 nTruncate; /* dbsize field from frame header */ + + /* Read and decode the next log frame. */ + rc = sqlite3OsRead(pWal->pWalFd, aFrame, szFrame, iOffset); + if( rc!=SQLITE_OK ) break; + isValid = walDecodeFrame(pWal, &pgno, &nTruncate, aData, aFrame); + if( !isValid ) break; + rc = walIndexAppend(pWal, iFrame, pgno); + if( NEVER(rc!=SQLITE_OK) ) break; + + /* If nTruncate is non-zero, this is a commit record. */ + if( nTruncate ){ + pWal->hdr.mxFrame = iFrame; + pWal->hdr.nPage = nTruncate; + pWal->hdr.szPage = (u16)((szPage&0xff00) | (szPage>>16)); + testcase( szPage<=32768 ); + testcase( szPage>=65536 ); + aFrameCksum[0] = pWal->hdr.aFrameCksum[0]; + aFrameCksum[1] = pWal->hdr.aFrameCksum[1]; + } + } + pWal->apWiData[iPg] = aShare; + nHdr = (iPg==0 ? WALINDEX_HDR_SIZE : 0); + nHdr32 = nHdr / sizeof(u32); +#ifndef SQLITE_SAFER_WALINDEX_RECOVERY + /* Memcpy() should work fine here, on all reasonable implementations. + ** Technically, memcpy() might change the destination to some + ** intermediate value before setting to the final value, and that might + ** cause a concurrent reader to malfunction. Memcpy() is allowed to + ** do that, according to the spec, but no memcpy() implementation that + ** we know of actually does that, which is why we say that memcpy() + ** is safe for this. Memcpy() is certainly a lot faster. + */ + memcpy(&aShare[nHdr32], &aPrivate[nHdr32], WALINDEX_PGSZ-nHdr); +#else + /* In the event that some platform is found for which memcpy() + ** changes the destination to some intermediate value before + ** setting the final value, this alternative copy routine is + ** provided. + */ + { + int i; + for(i=nHdr32; i<WALINDEX_PGSZ/sizeof(u32); i++){ + if( aShare[i]!=aPrivate[i] ){ + /* Atomic memory operations are not required here because if + ** the value needs to be changed, that means it is not being + ** accessed concurrently. */ + aShare[i] = aPrivate[i]; + } + } + } +#endif + if( iFrame<=iLast ) break; + } + + sqlite3_free(aFrame); + } + +finished: + if( rc==SQLITE_OK ){ + volatile WalCkptInfo *pInfo; + int i; + pWal->hdr.aFrameCksum[0] = aFrameCksum[0]; + pWal->hdr.aFrameCksum[1] = aFrameCksum[1]; + walIndexWriteHdr(pWal); + + /* Reset the checkpoint-header. This is safe because this thread is + ** currently holding locks that exclude all other writers and + ** checkpointers. Then set the values of read-mark slots 1 through N. + */ + pInfo = walCkptInfo(pWal); + pInfo->nBackfill = 0; + pInfo->nBackfillAttempted = pWal->hdr.mxFrame; + pInfo->aReadMark[0] = 0; + for(i=1; i<WAL_NREADER; i++){ + rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1); + if( rc==SQLITE_OK ){ + if( i==1 && pWal->hdr.mxFrame ){ + pInfo->aReadMark[i] = pWal->hdr.mxFrame; + }else{ + pInfo->aReadMark[i] = READMARK_NOT_USED; + } + walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1); + }else if( rc!=SQLITE_BUSY ){ + goto recovery_error; + } + } + + /* If more than one frame was recovered from the log file, report an + ** event via sqlite3_log(). This is to help with identifying performance + ** problems caused by applications routinely shutting down without + ** checkpointing the log file. + */ + if( pWal->hdr.nPage ){ + sqlite3_log(SQLITE_NOTICE_RECOVER_WAL, + "recovered %d frames from WAL file %s", + pWal->hdr.mxFrame, pWal->zWalName + ); + } + } + +recovery_error: + WALTRACE(("WAL%p: recovery %s\n", pWal, rc ? "failed" : "ok")); + walUnlockExclusive(pWal, iLock, WAL_READ_LOCK(0)-iLock); + return rc; +} + +/* +** Close an open wal-index. +*/ +static void walIndexClose(Wal *pWal, int isDelete){ + if( pWal->exclusiveMode==WAL_HEAPMEMORY_MODE || pWal->bShmUnreliable ){ + int i; + for(i=0; i<pWal->nWiData; i++){ + sqlite3_free((void *)pWal->apWiData[i]); + pWal->apWiData[i] = 0; + } + } + if( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE ){ + sqlite3OsShmUnmap(pWal->pDbFd, isDelete); + } +} + +/* +** Open a connection to the WAL file zWalName. The database file must +** already be opened on connection pDbFd. The buffer that zWalName points +** to must remain valid for the lifetime of the returned Wal* handle. +** +** A SHARED lock should be held on the database file when this function +** is called. The purpose of this SHARED lock is to prevent any other +** client from unlinking the WAL or wal-index file. If another process +** were to do this just after this client opened one of these files, the +** system would be badly broken. +** +** If the log file is successfully opened, SQLITE_OK is returned and +** *ppWal is set to point to a new WAL handle. If an error occurs, +** an SQLite error code is returned and *ppWal is left unmodified. +*/ +int sqlite3WalOpen( + sqlite3_vfs *pVfs, /* vfs module to open wal and wal-index */ + sqlite3_file *pDbFd, /* The open database file */ + const char *zWalName, /* Name of the WAL file */ + int bNoShm, /* True to run in heap-memory mode */ + i64 mxWalSize, /* Truncate WAL to this size on reset */ + Wal **ppWal /* OUT: Allocated Wal handle */ +){ + int rc; /* Return Code */ + Wal *pRet; /* Object to allocate and return */ + int flags; /* Flags passed to OsOpen() */ + + assert( zWalName && zWalName[0] ); + assert( pDbFd ); + + /* Verify the values of various constants. Any changes to the values + ** of these constants would result in an incompatible on-disk format + ** for the -shm file. Any change that causes one of these asserts to + ** fail is a backward compatibility problem, even if the change otherwise + ** works. + ** + ** This table also serves as a helpful cross-reference when trying to + ** interpret hex dumps of the -shm file. + */ + assert( 48 == sizeof(WalIndexHdr) ); + assert( 40 == sizeof(WalCkptInfo) ); + assert( 120 == WALINDEX_LOCK_OFFSET ); + assert( 136 == WALINDEX_HDR_SIZE ); + assert( 4096 == HASHTABLE_NPAGE ); + assert( 4062 == HASHTABLE_NPAGE_ONE ); + assert( 8192 == HASHTABLE_NSLOT ); + assert( 383 == HASHTABLE_HASH_1 ); + assert( 32768 == WALINDEX_PGSZ ); + assert( 8 == SQLITE_SHM_NLOCK ); + assert( 5 == WAL_NREADER ); + assert( 24 == WAL_FRAME_HDRSIZE ); + assert( 32 == WAL_HDRSIZE ); + assert( 120 == WALINDEX_LOCK_OFFSET + WAL_WRITE_LOCK ); + assert( 121 == WALINDEX_LOCK_OFFSET + WAL_CKPT_LOCK ); + assert( 122 == WALINDEX_LOCK_OFFSET + WAL_RECOVER_LOCK ); + assert( 123 == WALINDEX_LOCK_OFFSET + WAL_READ_LOCK(0) ); + assert( 124 == WALINDEX_LOCK_OFFSET + WAL_READ_LOCK(1) ); + assert( 125 == WALINDEX_LOCK_OFFSET + WAL_READ_LOCK(2) ); + assert( 126 == WALINDEX_LOCK_OFFSET + WAL_READ_LOCK(3) ); + assert( 127 == WALINDEX_LOCK_OFFSET + WAL_READ_LOCK(4) ); + + /* In the amalgamation, the os_unix.c and os_win.c source files come before + ** this source file. Verify that the #defines of the locking byte offsets + ** in os_unix.c and os_win.c agree with the WALINDEX_LOCK_OFFSET value. + ** For that matter, if the lock offset ever changes from its initial design + ** value of 120, we need to know that so there is an assert() to check it. + */ +#ifdef WIN_SHM_BASE + assert( WIN_SHM_BASE==WALINDEX_LOCK_OFFSET ); +#endif +#ifdef UNIX_SHM_BASE + assert( UNIX_SHM_BASE==WALINDEX_LOCK_OFFSET ); +#endif + + + /* Allocate an instance of struct Wal to return. */ + *ppWal = 0; + pRet = (Wal*)sqlite3MallocZero(sizeof(Wal) + pVfs->szOsFile); + if( !pRet ){ + return SQLITE_NOMEM_BKPT; + } + + pRet->pVfs = pVfs; + pRet->pWalFd = (sqlite3_file *)&pRet[1]; + pRet->pDbFd = pDbFd; + pRet->readLock = -1; + pRet->mxWalSize = mxWalSize; + pRet->zWalName = zWalName; + pRet->syncHeader = 1; + pRet->padToSectorBoundary = 1; + pRet->exclusiveMode = (bNoShm ? WAL_HEAPMEMORY_MODE: WAL_NORMAL_MODE); + + /* Open file handle on the write-ahead log file. */ + flags = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_WAL); + rc = sqlite3OsOpen(pVfs, zWalName, pRet->pWalFd, flags, &flags); + if( rc==SQLITE_OK && flags&SQLITE_OPEN_READONLY ){ + pRet->readOnly = WAL_RDONLY; + } + + if( rc!=SQLITE_OK ){ + walIndexClose(pRet, 0); + sqlite3OsClose(pRet->pWalFd); + sqlite3_free(pRet); + }else{ + int iDC = sqlite3OsDeviceCharacteristics(pDbFd); + if( iDC & SQLITE_IOCAP_SEQUENTIAL ){ pRet->syncHeader = 0; } + if( iDC & SQLITE_IOCAP_POWERSAFE_OVERWRITE ){ + pRet->padToSectorBoundary = 0; + } + *ppWal = pRet; + WALTRACE(("WAL%d: opened\n", pRet)); + } + return rc; +} + +/* +** Change the size to which the WAL file is trucated on each reset. +*/ +void sqlite3WalLimit(Wal *pWal, i64 iLimit){ + if( pWal ) pWal->mxWalSize = iLimit; +} + +/* +** Find the smallest page number out of all pages held in the WAL that +** has not been returned by any prior invocation of this method on the +** same WalIterator object. Write into *piFrame the frame index where +** that page was last written into the WAL. Write into *piPage the page +** number. +** +** Return 0 on success. If there are no pages in the WAL with a page +** number larger than *piPage, then return 1. +*/ +static int walIteratorNext( + WalIterator *p, /* Iterator */ + u32 *piPage, /* OUT: The page number of the next page */ + u32 *piFrame /* OUT: Wal frame index of next page */ +){ + u32 iMin; /* Result pgno must be greater than iMin */ + u32 iRet = 0xFFFFFFFF; /* 0xffffffff is never a valid page number */ + int i; /* For looping through segments */ + + iMin = p->iPrior; + assert( iMin<0xffffffff ); + for(i=p->nSegment-1; i>=0; i--){ + struct WalSegment *pSegment = &p->aSegment[i]; + while( pSegment->iNext<pSegment->nEntry ){ + u32 iPg = pSegment->aPgno[pSegment->aIndex[pSegment->iNext]]; + if( iPg>iMin ){ + if( iPg<iRet ){ + iRet = iPg; + *piFrame = pSegment->iZero + pSegment->aIndex[pSegment->iNext]; + } + break; + } + pSegment->iNext++; + } + } + + *piPage = p->iPrior = iRet; + return (iRet==0xFFFFFFFF); +} + +/* +** This function merges two sorted lists into a single sorted list. +** +** aLeft[] and aRight[] are arrays of indices. The sort key is +** aContent[aLeft[]] and aContent[aRight[]]. Upon entry, the following +** is guaranteed for all J<K: +** +** aContent[aLeft[J]] < aContent[aLeft[K]] +** aContent[aRight[J]] < aContent[aRight[K]] +** +** This routine overwrites aRight[] with a new (probably longer) sequence +** of indices such that the aRight[] contains every index that appears in +** either aLeft[] or the old aRight[] and such that the second condition +** above is still met. +** +** The aContent[aLeft[X]] values will be unique for all X. And the +** aContent[aRight[X]] values will be unique too. But there might be +** one or more combinations of X and Y such that +** +** aLeft[X]!=aRight[Y] && aContent[aLeft[X]] == aContent[aRight[Y]] +** +** When that happens, omit the aLeft[X] and use the aRight[Y] index. +*/ +static void walMerge( + const u32 *aContent, /* Pages in wal - keys for the sort */ + ht_slot *aLeft, /* IN: Left hand input list */ + int nLeft, /* IN: Elements in array *paLeft */ + ht_slot **paRight, /* IN/OUT: Right hand input list */ + int *pnRight, /* IN/OUT: Elements in *paRight */ + ht_slot *aTmp /* Temporary buffer */ +){ + int iLeft = 0; /* Current index in aLeft */ + int iRight = 0; /* Current index in aRight */ + int iOut = 0; /* Current index in output buffer */ + int nRight = *pnRight; + ht_slot *aRight = *paRight; + + assert( nLeft>0 && nRight>0 ); + while( iRight<nRight || iLeft<nLeft ){ + ht_slot logpage; + Pgno dbpage; + + if( (iLeft<nLeft) + && (iRight>=nRight || aContent[aLeft[iLeft]]<aContent[aRight[iRight]]) + ){ + logpage = aLeft[iLeft++]; + }else{ + logpage = aRight[iRight++]; + } + dbpage = aContent[logpage]; + + aTmp[iOut++] = logpage; + if( iLeft<nLeft && aContent[aLeft[iLeft]]==dbpage ) iLeft++; + + assert( iLeft>=nLeft || aContent[aLeft[iLeft]]>dbpage ); + assert( iRight>=nRight || aContent[aRight[iRight]]>dbpage ); + } + + *paRight = aLeft; + *pnRight = iOut; + memcpy(aLeft, aTmp, sizeof(aTmp[0])*iOut); +} + +/* +** Sort the elements in list aList using aContent[] as the sort key. +** Remove elements with duplicate keys, preferring to keep the +** larger aList[] values. +** +** The aList[] entries are indices into aContent[]. The values in +** aList[] are to be sorted so that for all J<K: +** +** aContent[aList[J]] < aContent[aList[K]] +** +** For any X and Y such that +** +** aContent[aList[X]] == aContent[aList[Y]] +** +** Keep the larger of the two values aList[X] and aList[Y] and discard +** the smaller. +*/ +static void walMergesort( + const u32 *aContent, /* Pages in wal */ + ht_slot *aBuffer, /* Buffer of at least *pnList items to use */ + ht_slot *aList, /* IN/OUT: List to sort */ + int *pnList /* IN/OUT: Number of elements in aList[] */ +){ + struct Sublist { + int nList; /* Number of elements in aList */ + ht_slot *aList; /* Pointer to sub-list content */ + }; + + const int nList = *pnList; /* Size of input list */ + int nMerge = 0; /* Number of elements in list aMerge */ + ht_slot *aMerge = 0; /* List to be merged */ + int iList; /* Index into input list */ + u32 iSub = 0; /* Index into aSub array */ + struct Sublist aSub[13]; /* Array of sub-lists */ + + memset(aSub, 0, sizeof(aSub)); + assert( nList<=HASHTABLE_NPAGE && nList>0 ); + assert( HASHTABLE_NPAGE==(1<<(ArraySize(aSub)-1)) ); + + for(iList=0; iList<nList; iList++){ + nMerge = 1; + aMerge = &aList[iList]; + for(iSub=0; iList & (1<<iSub); iSub++){ + struct Sublist *p; + assert( iSub<ArraySize(aSub) ); + p = &aSub[iSub]; + assert( p->aList && p->nList<=(1<<iSub) ); + assert( p->aList==&aList[iList&~((2<<iSub)-1)] ); + walMerge(aContent, p->aList, p->nList, &aMerge, &nMerge, aBuffer); + } + aSub[iSub].aList = aMerge; + aSub[iSub].nList = nMerge; + } + + for(iSub++; iSub<ArraySize(aSub); iSub++){ + if( nList & (1<<iSub) ){ + struct Sublist *p; + assert( iSub<ArraySize(aSub) ); + p = &aSub[iSub]; + assert( p->nList<=(1<<iSub) ); + assert( p->aList==&aList[nList&~((2<<iSub)-1)] ); + walMerge(aContent, p->aList, p->nList, &aMerge, &nMerge, aBuffer); + } + } + assert( aMerge==aList ); + *pnList = nMerge; + +#ifdef SQLITE_DEBUG + { + int i; + for(i=1; i<*pnList; i++){ + assert( aContent[aList[i]] > aContent[aList[i-1]] ); + } + } +#endif +} + +/* +** Free an iterator allocated by walIteratorInit(). +*/ +static void walIteratorFree(WalIterator *p){ + sqlite3_free(p); +} + +/* +** Construct a WalInterator object that can be used to loop over all +** pages in the WAL following frame nBackfill in ascending order. Frames +** nBackfill or earlier may be included - excluding them is an optimization +** only. The caller must hold the checkpoint lock. +** +** On success, make *pp point to the newly allocated WalInterator object +** return SQLITE_OK. Otherwise, return an error code. If this routine +** returns an error, the value of *pp is undefined. +** +** The calling routine should invoke walIteratorFree() to destroy the +** WalIterator object when it has finished with it. +*/ +static int walIteratorInit(Wal *pWal, u32 nBackfill, WalIterator **pp){ + WalIterator *p; /* Return value */ + int nSegment; /* Number of segments to merge */ + u32 iLast; /* Last frame in log */ + sqlite3_int64 nByte; /* Number of bytes to allocate */ + int i; /* Iterator variable */ + ht_slot *aTmp; /* Temp space used by merge-sort */ + int rc = SQLITE_OK; /* Return Code */ + + /* This routine only runs while holding the checkpoint lock. And + ** it only runs if there is actually content in the log (mxFrame>0). + */ + assert( pWal->ckptLock && pWal->hdr.mxFrame>0 ); + iLast = pWal->hdr.mxFrame; + + /* Allocate space for the WalIterator object. */ + nSegment = walFramePage(iLast) + 1; + nByte = sizeof(WalIterator) + + (nSegment-1)*sizeof(struct WalSegment) + + iLast*sizeof(ht_slot); + p = (WalIterator *)sqlite3_malloc64(nByte); + if( !p ){ + return SQLITE_NOMEM_BKPT; + } + memset(p, 0, nByte); + p->nSegment = nSegment; + + /* Allocate temporary space used by the merge-sort routine. This block + ** of memory will be freed before this function returns. + */ + aTmp = (ht_slot *)sqlite3_malloc64( + sizeof(ht_slot) * (iLast>HASHTABLE_NPAGE?HASHTABLE_NPAGE:iLast) + ); + if( !aTmp ){ + rc = SQLITE_NOMEM_BKPT; + } + + for(i=walFramePage(nBackfill+1); rc==SQLITE_OK && i<nSegment; i++){ + WalHashLoc sLoc; + + rc = walHashGet(pWal, i, &sLoc); + if( rc==SQLITE_OK ){ + int j; /* Counter variable */ + int nEntry; /* Number of entries in this segment */ + ht_slot *aIndex; /* Sorted index for this segment */ + + if( (i+1)==nSegment ){ + nEntry = (int)(iLast - sLoc.iZero); + }else{ + nEntry = (int)((u32*)sLoc.aHash - (u32*)sLoc.aPgno); + } + aIndex = &((ht_slot *)&p->aSegment[p->nSegment])[sLoc.iZero]; + sLoc.iZero++; + + for(j=0; j<nEntry; j++){ + aIndex[j] = (ht_slot)j; + } + walMergesort((u32 *)sLoc.aPgno, aTmp, aIndex, &nEntry); + p->aSegment[i].iZero = sLoc.iZero; + p->aSegment[i].nEntry = nEntry; + p->aSegment[i].aIndex = aIndex; + p->aSegment[i].aPgno = (u32 *)sLoc.aPgno; + } + } + sqlite3_free(aTmp); + + if( rc!=SQLITE_OK ){ + walIteratorFree(p); + p = 0; + } + *pp = p; + return rc; +} + +#ifdef SQLITE_ENABLE_SETLK_TIMEOUT +/* +** Attempt to enable blocking locks. Blocking locks are enabled only if (a) +** they are supported by the VFS, and (b) the database handle is configured +** with a busy-timeout. Return 1 if blocking locks are successfully enabled, +** or 0 otherwise. +*/ +static int walEnableBlocking(Wal *pWal){ + int res = 0; + if( pWal->db ){ + int tmout = pWal->db->busyTimeout; + if( tmout ){ + int rc; + rc = sqlite3OsFileControl( + pWal->pDbFd, SQLITE_FCNTL_LOCK_TIMEOUT, (void*)&tmout + ); + res = (rc==SQLITE_OK); + } + } + return res; +} + +/* +** Disable blocking locks. +*/ +static void walDisableBlocking(Wal *pWal){ + int tmout = 0; + sqlite3OsFileControl(pWal->pDbFd, SQLITE_FCNTL_LOCK_TIMEOUT, (void*)&tmout); +} + +/* +** If parameter bLock is true, attempt to enable blocking locks, take +** the WRITER lock, and then disable blocking locks. If blocking locks +** cannot be enabled, no attempt to obtain the WRITER lock is made. Return +** an SQLite error code if an error occurs, or SQLITE_OK otherwise. It is not +** an error if blocking locks can not be enabled. +** +** If the bLock parameter is false and the WRITER lock is held, release it. +*/ +int sqlite3WalWriteLock(Wal *pWal, int bLock){ + int rc = SQLITE_OK; + assert( pWal->readLock<0 || bLock==0 ); + if( bLock ){ + assert( pWal->db ); + if( walEnableBlocking(pWal) ){ + rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1); + if( rc==SQLITE_OK ){ + pWal->writeLock = 1; + } + walDisableBlocking(pWal); + } + }else if( pWal->writeLock ){ + walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1); + pWal->writeLock = 0; + } + return rc; +} + +/* +** Set the database handle used to determine if blocking locks are required. +*/ +void sqlite3WalDb(Wal *pWal, sqlite3 *db){ + pWal->db = db; +} + +/* +** Take an exclusive WRITE lock. Blocking if so configured. +*/ +static int walLockWriter(Wal *pWal){ + int rc; + walEnableBlocking(pWal); + rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1); + walDisableBlocking(pWal); + return rc; +} +#else +# define walEnableBlocking(x) 0 +# define walDisableBlocking(x) +# define walLockWriter(pWal) walLockExclusive((pWal), WAL_WRITE_LOCK, 1) +# define sqlite3WalDb(pWal, db) +#endif /* ifdef SQLITE_ENABLE_SETLK_TIMEOUT */ + + +/* +** Attempt to obtain the exclusive WAL lock defined by parameters lockIdx and +** n. If the attempt fails and parameter xBusy is not NULL, then it is a +** busy-handler function. Invoke it and retry the lock until either the +** lock is successfully obtained or the busy-handler returns 0. +*/ +static int walBusyLock( + Wal *pWal, /* WAL connection */ + int (*xBusy)(void*), /* Function to call when busy */ + void *pBusyArg, /* Context argument for xBusyHandler */ + int lockIdx, /* Offset of first byte to lock */ + int n /* Number of bytes to lock */ +){ + int rc; + do { + rc = walLockExclusive(pWal, lockIdx, n); + }while( xBusy && rc==SQLITE_BUSY && xBusy(pBusyArg) ); +#ifdef SQLITE_ENABLE_SETLK_TIMEOUT + if( rc==SQLITE_BUSY_TIMEOUT ){ + walDisableBlocking(pWal); + rc = SQLITE_BUSY; + } +#endif + return rc; +} + +/* +** The cache of the wal-index header must be valid to call this function. +** Return the page-size in bytes used by the database. +*/ +static int walPagesize(Wal *pWal){ + return (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16); +} + +/* +** The following is guaranteed when this function is called: +** +** a) the WRITER lock is held, +** b) the entire log file has been checkpointed, and +** c) any existing readers are reading exclusively from the database +** file - there are no readers that may attempt to read a frame from +** the log file. +** +** This function updates the shared-memory structures so that the next +** client to write to the database (which may be this one) does so by +** writing frames into the start of the log file. +** +** The value of parameter salt1 is used as the aSalt[1] value in the +** new wal-index header. It should be passed a pseudo-random value (i.e. +** one obtained from sqlite3_randomness()). +*/ +static void walRestartHdr(Wal *pWal, u32 salt1){ + volatile WalCkptInfo *pInfo = walCkptInfo(pWal); + int i; /* Loop counter */ + u32 *aSalt = pWal->hdr.aSalt; /* Big-endian salt values */ + pWal->nCkpt++; + pWal->hdr.mxFrame = 0; + sqlite3Put4byte((u8*)&aSalt[0], 1 + sqlite3Get4byte((u8*)&aSalt[0])); + memcpy(&pWal->hdr.aSalt[1], &salt1, 4); + walIndexWriteHdr(pWal); + AtomicStore(&pInfo->nBackfill, 0); + pInfo->nBackfillAttempted = 0; + pInfo->aReadMark[1] = 0; + for(i=2; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED; + assert( pInfo->aReadMark[0]==0 ); +} + +/* +** Copy as much content as we can from the WAL back into the database file +** in response to an sqlite3_wal_checkpoint() request or the equivalent. +** +** The amount of information copies from WAL to database might be limited +** by active readers. This routine will never overwrite a database page +** that a concurrent reader might be using. +** +** All I/O barrier operations (a.k.a fsyncs) occur in this routine when +** SQLite is in WAL-mode in synchronous=NORMAL. That means that if +** checkpoints are always run by a background thread or background +** process, foreground threads will never block on a lengthy fsync call. +** +** Fsync is called on the WAL before writing content out of the WAL and +** into the database. This ensures that if the new content is persistent +** in the WAL and can be recovered following a power-loss or hard reset. +** +** Fsync is also called on the database file if (and only if) the entire +** WAL content is copied into the database file. This second fsync makes +** it safe to delete the WAL since the new content will persist in the +** database file. +** +** This routine uses and updates the nBackfill field of the wal-index header. +** This is the only routine that will increase the value of nBackfill. +** (A WAL reset or recovery will revert nBackfill to zero, but not increase +** its value.) +** +** The caller must be holding sufficient locks to ensure that no other +** checkpoint is running (in any other thread or process) at the same +** time. +*/ +static int walCheckpoint( + Wal *pWal, /* Wal connection */ + sqlite3 *db, /* Check for interrupts on this handle */ + int eMode, /* One of PASSIVE, FULL or RESTART */ + int (*xBusy)(void*), /* Function to call when busy */ + void *pBusyArg, /* Context argument for xBusyHandler */ + int sync_flags, /* Flags for OsSync() (or 0) */ + u8 *zBuf /* Temporary buffer to use */ +){ + int rc = SQLITE_OK; /* Return code */ + int szPage; /* Database page-size */ + WalIterator *pIter = 0; /* Wal iterator context */ + u32 iDbpage = 0; /* Next database page to write */ + u32 iFrame = 0; /* Wal frame containing data for iDbpage */ + u32 mxSafeFrame; /* Max frame that can be backfilled */ + u32 mxPage; /* Max database page to write */ + int i; /* Loop counter */ + volatile WalCkptInfo *pInfo; /* The checkpoint status information */ + + szPage = walPagesize(pWal); + testcase( szPage<=32768 ); + testcase( szPage>=65536 ); + pInfo = walCkptInfo(pWal); + if( pInfo->nBackfill<pWal->hdr.mxFrame ){ + + /* EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked + ** in the SQLITE_CHECKPOINT_PASSIVE mode. */ + assert( eMode!=SQLITE_CHECKPOINT_PASSIVE || xBusy==0 ); + + /* Compute in mxSafeFrame the index of the last frame of the WAL that is + ** safe to write into the database. Frames beyond mxSafeFrame might + ** overwrite database pages that are in use by active readers and thus + ** cannot be backfilled from the WAL. + */ + mxSafeFrame = pWal->hdr.mxFrame; + mxPage = pWal->hdr.nPage; + for(i=1; i<WAL_NREADER; i++){ + u32 y = AtomicLoad(pInfo->aReadMark+i); + if( mxSafeFrame>y ){ + assert( y<=pWal->hdr.mxFrame ); + rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(i), 1); + if( rc==SQLITE_OK ){ + u32 iMark = (i==1 ? mxSafeFrame : READMARK_NOT_USED); + AtomicStore(pInfo->aReadMark+i, iMark); + walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1); + }else if( rc==SQLITE_BUSY ){ + mxSafeFrame = y; + xBusy = 0; + }else{ + goto walcheckpoint_out; + } + } + } + + /* Allocate the iterator */ + if( pInfo->nBackfill<mxSafeFrame ){ + rc = walIteratorInit(pWal, pInfo->nBackfill, &pIter); + assert( rc==SQLITE_OK || pIter==0 ); + } + + if( pIter + && (rc = walBusyLock(pWal,xBusy,pBusyArg,WAL_READ_LOCK(0),1))==SQLITE_OK + ){ + u32 nBackfill = pInfo->nBackfill; + + pInfo->nBackfillAttempted = mxSafeFrame; + + /* Sync the WAL to disk */ + rc = sqlite3OsSync(pWal->pWalFd, CKPT_SYNC_FLAGS(sync_flags)); + + /* If the database may grow as a result of this checkpoint, hint + ** about the eventual size of the db file to the VFS layer. + */ + if( rc==SQLITE_OK ){ + i64 nReq = ((i64)mxPage * szPage); + i64 nSize; /* Current size of database file */ + sqlite3OsFileControl(pWal->pDbFd, SQLITE_FCNTL_CKPT_START, 0); + rc = sqlite3OsFileSize(pWal->pDbFd, &nSize); + if( rc==SQLITE_OK && nSize<nReq ){ + if( (nSize+65536+(i64)pWal->hdr.mxFrame*szPage)<nReq ){ + /* If the size of the final database is larger than the current + ** database plus the amount of data in the wal file, plus the + ** maximum size of the pending-byte page (65536 bytes), then + ** must be corruption somewhere. */ + rc = SQLITE_CORRUPT_BKPT; + }else{ + sqlite3OsFileControlHint(pWal->pDbFd, SQLITE_FCNTL_SIZE_HINT,&nReq); + } + } + + } + + /* Iterate through the contents of the WAL, copying data to the db file */ + while( rc==SQLITE_OK && 0==walIteratorNext(pIter, &iDbpage, &iFrame) ){ + i64 iOffset; + assert( walFramePgno(pWal, iFrame)==iDbpage ); + if( AtomicLoad(&db->u1.isInterrupted) ){ + rc = db->mallocFailed ? SQLITE_NOMEM_BKPT : SQLITE_INTERRUPT; + break; + } + if( iFrame<=nBackfill || iFrame>mxSafeFrame || iDbpage>mxPage ){ + continue; + } + iOffset = walFrameOffset(iFrame, szPage) + WAL_FRAME_HDRSIZE; + /* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL file */ + rc = sqlite3OsRead(pWal->pWalFd, zBuf, szPage, iOffset); + if( rc!=SQLITE_OK ) break; + iOffset = (iDbpage-1)*(i64)szPage; + testcase( IS_BIG_INT(iOffset) ); + rc = sqlite3OsWrite(pWal->pDbFd, zBuf, szPage, iOffset); + if( rc!=SQLITE_OK ) break; + } + sqlite3OsFileControl(pWal->pDbFd, SQLITE_FCNTL_CKPT_DONE, 0); + + /* If work was actually accomplished... */ + if( rc==SQLITE_OK ){ + if( mxSafeFrame==walIndexHdr(pWal)->mxFrame ){ + i64 szDb = pWal->hdr.nPage*(i64)szPage; + testcase( IS_BIG_INT(szDb) ); + rc = sqlite3OsTruncate(pWal->pDbFd, szDb); + if( rc==SQLITE_OK ){ + rc = sqlite3OsSync(pWal->pDbFd, CKPT_SYNC_FLAGS(sync_flags)); + } + } + if( rc==SQLITE_OK ){ + AtomicStore(&pInfo->nBackfill, mxSafeFrame); + } + } + + /* Release the reader lock held while backfilling */ + walUnlockExclusive(pWal, WAL_READ_LOCK(0), 1); + } + + if( rc==SQLITE_BUSY ){ + /* Reset the return code so as not to report a checkpoint failure + ** just because there are active readers. */ + rc = SQLITE_OK; + } + } + + /* If this is an SQLITE_CHECKPOINT_RESTART or TRUNCATE operation, and the + ** entire wal file has been copied into the database file, then block + ** until all readers have finished using the wal file. This ensures that + ** the next process to write to the database restarts the wal file. + */ + if( rc==SQLITE_OK && eMode!=SQLITE_CHECKPOINT_PASSIVE ){ + assert( pWal->writeLock ); + if( pInfo->nBackfill<pWal->hdr.mxFrame ){ + rc = SQLITE_BUSY; + }else if( eMode>=SQLITE_CHECKPOINT_RESTART ){ + u32 salt1; + sqlite3_randomness(4, &salt1); + assert( pInfo->nBackfill==pWal->hdr.mxFrame ); + rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(1), WAL_NREADER-1); + if( rc==SQLITE_OK ){ + if( eMode==SQLITE_CHECKPOINT_TRUNCATE ){ + /* IMPLEMENTATION-OF: R-44699-57140 This mode works the same way as + ** SQLITE_CHECKPOINT_RESTART with the addition that it also + ** truncates the log file to zero bytes just prior to a + ** successful return. + ** + ** In theory, it might be safe to do this without updating the + ** wal-index header in shared memory, as all subsequent reader or + ** writer clients should see that the entire log file has been + ** checkpointed and behave accordingly. This seems unsafe though, + ** as it would leave the system in a state where the contents of + ** the wal-index header do not match the contents of the + ** file-system. To avoid this, update the wal-index header to + ** indicate that the log file contains zero valid frames. */ + walRestartHdr(pWal, salt1); + rc = sqlite3OsTruncate(pWal->pWalFd, 0); + } + walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1); + } + } + } + + walcheckpoint_out: + walIteratorFree(pIter); + return rc; +} + +/* +** If the WAL file is currently larger than nMax bytes in size, truncate +** it to exactly nMax bytes. If an error occurs while doing so, ignore it. +*/ +static void walLimitSize(Wal *pWal, i64 nMax){ + i64 sz; + int rx; + sqlite3BeginBenignMalloc(); + rx = sqlite3OsFileSize(pWal->pWalFd, &sz); + if( rx==SQLITE_OK && (sz > nMax ) ){ + rx = sqlite3OsTruncate(pWal->pWalFd, nMax); + } + sqlite3EndBenignMalloc(); + if( rx ){ + sqlite3_log(rx, "cannot limit WAL size: %s", pWal->zWalName); + } +} + +/* +** Close a connection to a log file. +*/ +int sqlite3WalClose( + Wal *pWal, /* Wal to close */ + sqlite3 *db, /* For interrupt flag */ + int sync_flags, /* Flags to pass to OsSync() (or 0) */ + int nBuf, + u8 *zBuf /* Buffer of at least nBuf bytes */ +){ + int rc = SQLITE_OK; + if( pWal ){ + int isDelete = 0; /* True to unlink wal and wal-index files */ + + /* If an EXCLUSIVE lock can be obtained on the database file (using the + ** ordinary, rollback-mode locking methods, this guarantees that the + ** connection associated with this log file is the only connection to + ** the database. In this case checkpoint the database and unlink both + ** the wal and wal-index files. + ** + ** The EXCLUSIVE lock is not released before returning. + */ + if( zBuf!=0 + && SQLITE_OK==(rc = sqlite3OsLock(pWal->pDbFd, SQLITE_LOCK_EXCLUSIVE)) + ){ + if( pWal->exclusiveMode==WAL_NORMAL_MODE ){ + pWal->exclusiveMode = WAL_EXCLUSIVE_MODE; + } + rc = sqlite3WalCheckpoint(pWal, db, + SQLITE_CHECKPOINT_PASSIVE, 0, 0, sync_flags, nBuf, zBuf, 0, 0 + ); + if( rc==SQLITE_OK ){ + int bPersist = -1; + sqlite3OsFileControlHint( + pWal->pDbFd, SQLITE_FCNTL_PERSIST_WAL, &bPersist + ); + if( bPersist!=1 ){ + /* Try to delete the WAL file if the checkpoint completed and + ** fsyned (rc==SQLITE_OK) and if we are not in persistent-wal + ** mode (!bPersist) */ + isDelete = 1; + }else if( pWal->mxWalSize>=0 ){ + /* Try to truncate the WAL file to zero bytes if the checkpoint + ** completed and fsynced (rc==SQLITE_OK) and we are in persistent + ** WAL mode (bPersist) and if the PRAGMA journal_size_limit is a + ** non-negative value (pWal->mxWalSize>=0). Note that we truncate + ** to zero bytes as truncating to the journal_size_limit might + ** leave a corrupt WAL file on disk. */ + walLimitSize(pWal, 0); + } + } + } + + walIndexClose(pWal, isDelete); + sqlite3OsClose(pWal->pWalFd); + if( isDelete ){ + sqlite3BeginBenignMalloc(); + sqlite3OsDelete(pWal->pVfs, pWal->zWalName, 0); + sqlite3EndBenignMalloc(); + } + WALTRACE(("WAL%p: closed\n", pWal)); + sqlite3_free((void *)pWal->apWiData); + sqlite3_free(pWal); + } + return rc; +} + +/* +** Try to read the wal-index header. Return 0 on success and 1 if +** there is a problem. +** +** The wal-index is in shared memory. Another thread or process might +** be writing the header at the same time this procedure is trying to +** read it, which might result in inconsistency. A dirty read is detected +** by verifying that both copies of the header are the same and also by +** a checksum on the header. +** +** If and only if the read is consistent and the header is different from +** pWal->hdr, then pWal->hdr is updated to the content of the new header +** and *pChanged is set to 1. +** +** If the checksum cannot be verified return non-zero. If the header +** is read successfully and the checksum verified, return zero. +*/ +static SQLITE_NO_TSAN int walIndexTryHdr(Wal *pWal, int *pChanged){ + u32 aCksum[2]; /* Checksum on the header content */ + WalIndexHdr h1, h2; /* Two copies of the header content */ + WalIndexHdr volatile *aHdr; /* Header in shared memory */ + + /* The first page of the wal-index must be mapped at this point. */ + assert( pWal->nWiData>0 && pWal->apWiData[0] ); + + /* Read the header. This might happen concurrently with a write to the + ** same area of shared memory on a different CPU in a SMP, + ** meaning it is possible that an inconsistent snapshot is read + ** from the file. If this happens, return non-zero. + ** + ** tag-20200519-1: + ** There are two copies of the header at the beginning of the wal-index. + ** When reading, read [0] first then [1]. Writes are in the reverse order. + ** Memory barriers are used to prevent the compiler or the hardware from + ** reordering the reads and writes. TSAN and similar tools can sometimes + ** give false-positive warnings about these accesses because the tools do not + ** account for the double-read and the memory barrier. The use of mutexes + ** here would be problematic as the memory being accessed is potentially + ** shared among multiple processes and not all mutex implementions work + ** reliably in that environment. + */ + aHdr = walIndexHdr(pWal); + memcpy(&h1, (void *)&aHdr[0], sizeof(h1)); /* Possible TSAN false-positive */ + walShmBarrier(pWal); + memcpy(&h2, (void *)&aHdr[1], sizeof(h2)); + + if( memcmp(&h1, &h2, sizeof(h1))!=0 ){ + return 1; /* Dirty read */ + } + if( h1.isInit==0 ){ + return 1; /* Malformed header - probably all zeros */ + } + walChecksumBytes(1, (u8*)&h1, sizeof(h1)-sizeof(h1.aCksum), 0, aCksum); + if( aCksum[0]!=h1.aCksum[0] || aCksum[1]!=h1.aCksum[1] ){ + return 1; /* Checksum does not match */ + } + + if( memcmp(&pWal->hdr, &h1, sizeof(WalIndexHdr)) ){ + *pChanged = 1; + memcpy(&pWal->hdr, &h1, sizeof(WalIndexHdr)); + pWal->szPage = (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16); + testcase( pWal->szPage<=32768 ); + testcase( pWal->szPage>=65536 ); + } + + /* The header was successfully read. Return zero. */ + return 0; +} + +/* +** This is the value that walTryBeginRead returns when it needs to +** be retried. +*/ +#define WAL_RETRY (-1) + +/* +** Read the wal-index header from the wal-index and into pWal->hdr. +** If the wal-header appears to be corrupt, try to reconstruct the +** wal-index from the WAL before returning. +** +** Set *pChanged to 1 if the wal-index header value in pWal->hdr is +** changed by this operation. If pWal->hdr is unchanged, set *pChanged +** to 0. +** +** If the wal-index header is successfully read, return SQLITE_OK. +** Otherwise an SQLite error code. +*/ +static int walIndexReadHdr(Wal *pWal, int *pChanged){ + int rc; /* Return code */ + int badHdr; /* True if a header read failed */ + volatile u32 *page0; /* Chunk of wal-index containing header */ + + /* Ensure that page 0 of the wal-index (the page that contains the + ** wal-index header) is mapped. Return early if an error occurs here. + */ + assert( pChanged ); + rc = walIndexPage(pWal, 0, &page0); + if( rc!=SQLITE_OK ){ + assert( rc!=SQLITE_READONLY ); /* READONLY changed to OK in walIndexPage */ + if( rc==SQLITE_READONLY_CANTINIT ){ + /* The SQLITE_READONLY_CANTINIT return means that the shared-memory + ** was openable but is not writable, and this thread is unable to + ** confirm that another write-capable connection has the shared-memory + ** open, and hence the content of the shared-memory is unreliable, + ** since the shared-memory might be inconsistent with the WAL file + ** and there is no writer on hand to fix it. */ + assert( page0==0 ); + assert( pWal->writeLock==0 ); + assert( pWal->readOnly & WAL_SHM_RDONLY ); + pWal->bShmUnreliable = 1; + pWal->exclusiveMode = WAL_HEAPMEMORY_MODE; + *pChanged = 1; + }else{ + return rc; /* Any other non-OK return is just an error */ + } + }else{ + /* page0 can be NULL if the SHM is zero bytes in size and pWal->writeLock + ** is zero, which prevents the SHM from growing */ + testcase( page0!=0 ); + } + assert( page0!=0 || pWal->writeLock==0 ); + + /* If the first page of the wal-index has been mapped, try to read the + ** wal-index header immediately, without holding any lock. This usually + ** works, but may fail if the wal-index header is corrupt or currently + ** being modified by another thread or process. + */ + badHdr = (page0 ? walIndexTryHdr(pWal, pChanged) : 1); + + /* If the first attempt failed, it might have been due to a race + ** with a writer. So get a WRITE lock and try again. + */ + if( badHdr ){ + if( pWal->bShmUnreliable==0 && (pWal->readOnly & WAL_SHM_RDONLY) ){ + if( SQLITE_OK==(rc = walLockShared(pWal, WAL_WRITE_LOCK)) ){ + walUnlockShared(pWal, WAL_WRITE_LOCK); + rc = SQLITE_READONLY_RECOVERY; + } + }else{ + int bWriteLock = pWal->writeLock; + if( bWriteLock || SQLITE_OK==(rc = walLockWriter(pWal)) ){ + pWal->writeLock = 1; + if( SQLITE_OK==(rc = walIndexPage(pWal, 0, &page0)) ){ + badHdr = walIndexTryHdr(pWal, pChanged); + if( badHdr ){ + /* If the wal-index header is still malformed even while holding + ** a WRITE lock, it can only mean that the header is corrupted and + ** needs to be reconstructed. So run recovery to do exactly that. + */ + rc = walIndexRecover(pWal); + *pChanged = 1; + } + } + if( bWriteLock==0 ){ + pWal->writeLock = 0; + walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1); + } + } + } + } + + /* If the header is read successfully, check the version number to make + ** sure the wal-index was not constructed with some future format that + ** this version of SQLite cannot understand. + */ + if( badHdr==0 && pWal->hdr.iVersion!=WALINDEX_MAX_VERSION ){ + rc = SQLITE_CANTOPEN_BKPT; + } + if( pWal->bShmUnreliable ){ + if( rc!=SQLITE_OK ){ + walIndexClose(pWal, 0); + pWal->bShmUnreliable = 0; + assert( pWal->nWiData>0 && pWal->apWiData[0]==0 ); + /* walIndexRecover() might have returned SHORT_READ if a concurrent + ** writer truncated the WAL out from under it. If that happens, it + ** indicates that a writer has fixed the SHM file for us, so retry */ + if( rc==SQLITE_IOERR_SHORT_READ ) rc = WAL_RETRY; + } + pWal->exclusiveMode = WAL_NORMAL_MODE; + } + + return rc; +} + +/* +** Open a transaction in a connection where the shared-memory is read-only +** and where we cannot verify that there is a separate write-capable connection +** on hand to keep the shared-memory up-to-date with the WAL file. +** +** This can happen, for example, when the shared-memory is implemented by +** memory-mapping a *-shm file, where a prior writer has shut down and +** left the *-shm file on disk, and now the present connection is trying +** to use that database but lacks write permission on the *-shm file. +** Other scenarios are also possible, depending on the VFS implementation. +** +** Precondition: +** +** The *-wal file has been read and an appropriate wal-index has been +** constructed in pWal->apWiData[] using heap memory instead of shared +** memory. +** +** If this function returns SQLITE_OK, then the read transaction has +** been successfully opened. In this case output variable (*pChanged) +** is set to true before returning if the caller should discard the +** contents of the page cache before proceeding. Or, if it returns +** WAL_RETRY, then the heap memory wal-index has been discarded and +** the caller should retry opening the read transaction from the +** beginning (including attempting to map the *-shm file). +** +** If an error occurs, an SQLite error code is returned. +*/ +static int walBeginShmUnreliable(Wal *pWal, int *pChanged){ + i64 szWal; /* Size of wal file on disk in bytes */ + i64 iOffset; /* Current offset when reading wal file */ + u8 aBuf[WAL_HDRSIZE]; /* Buffer to load WAL header into */ + u8 *aFrame = 0; /* Malloc'd buffer to load entire frame */ + int szFrame; /* Number of bytes in buffer aFrame[] */ + u8 *aData; /* Pointer to data part of aFrame buffer */ + volatile void *pDummy; /* Dummy argument for xShmMap */ + int rc; /* Return code */ + u32 aSaveCksum[2]; /* Saved copy of pWal->hdr.aFrameCksum */ + + assert( pWal->bShmUnreliable ); + assert( pWal->readOnly & WAL_SHM_RDONLY ); + assert( pWal->nWiData>0 && pWal->apWiData[0] ); + + /* Take WAL_READ_LOCK(0). This has the effect of preventing any + ** writers from running a checkpoint, but does not stop them + ** from running recovery. */ + rc = walLockShared(pWal, WAL_READ_LOCK(0)); + if( rc!=SQLITE_OK ){ + if( rc==SQLITE_BUSY ) rc = WAL_RETRY; + goto begin_unreliable_shm_out; + } + pWal->readLock = 0; + + /* Check to see if a separate writer has attached to the shared-memory area, + ** thus making the shared-memory "reliable" again. Do this by invoking + ** the xShmMap() routine of the VFS and looking to see if the return + ** is SQLITE_READONLY instead of SQLITE_READONLY_CANTINIT. + ** + ** If the shared-memory is now "reliable" return WAL_RETRY, which will + ** cause the heap-memory WAL-index to be discarded and the actual + ** shared memory to be used in its place. + ** + ** This step is important because, even though this connection is holding + ** the WAL_READ_LOCK(0) which prevents a checkpoint, a writer might + ** have already checkpointed the WAL file and, while the current + ** is active, wrap the WAL and start overwriting frames that this + ** process wants to use. + ** + ** Once sqlite3OsShmMap() has been called for an sqlite3_file and has + ** returned any SQLITE_READONLY value, it must return only SQLITE_READONLY + ** or SQLITE_READONLY_CANTINIT or some error for all subsequent invocations, + ** even if some external agent does a "chmod" to make the shared-memory + ** writable by us, until sqlite3OsShmUnmap() has been called. + ** This is a requirement on the VFS implementation. + */ + rc = sqlite3OsShmMap(pWal->pDbFd, 0, WALINDEX_PGSZ, 0, &pDummy); + assert( rc!=SQLITE_OK ); /* SQLITE_OK not possible for read-only connection */ + if( rc!=SQLITE_READONLY_CANTINIT ){ + rc = (rc==SQLITE_READONLY ? WAL_RETRY : rc); + goto begin_unreliable_shm_out; + } + + /* We reach this point only if the real shared-memory is still unreliable. + ** Assume the in-memory WAL-index substitute is correct and load it + ** into pWal->hdr. + */ + memcpy(&pWal->hdr, (void*)walIndexHdr(pWal), sizeof(WalIndexHdr)); + + /* Make sure some writer hasn't come in and changed the WAL file out + ** from under us, then disconnected, while we were not looking. + */ + rc = sqlite3OsFileSize(pWal->pWalFd, &szWal); + if( rc!=SQLITE_OK ){ + goto begin_unreliable_shm_out; + } + if( szWal<WAL_HDRSIZE ){ + /* If the wal file is too small to contain a wal-header and the + ** wal-index header has mxFrame==0, then it must be safe to proceed + ** reading the database file only. However, the page cache cannot + ** be trusted, as a read/write connection may have connected, written + ** the db, run a checkpoint, truncated the wal file and disconnected + ** since this client's last read transaction. */ + *pChanged = 1; + rc = (pWal->hdr.mxFrame==0 ? SQLITE_OK : WAL_RETRY); + goto begin_unreliable_shm_out; + } + + /* Check the salt keys at the start of the wal file still match. */ + rc = sqlite3OsRead(pWal->pWalFd, aBuf, WAL_HDRSIZE, 0); + if( rc!=SQLITE_OK ){ + goto begin_unreliable_shm_out; + } + if( memcmp(&pWal->hdr.aSalt, &aBuf[16], 8) ){ + /* Some writer has wrapped the WAL file while we were not looking. + ** Return WAL_RETRY which will cause the in-memory WAL-index to be + ** rebuilt. */ + rc = WAL_RETRY; + goto begin_unreliable_shm_out; + } + + /* Allocate a buffer to read frames into */ + assert( (pWal->szPage & (pWal->szPage-1))==0 ); + assert( pWal->szPage>=512 && pWal->szPage<=65536 ); + szFrame = pWal->szPage + WAL_FRAME_HDRSIZE; + aFrame = (u8 *)sqlite3_malloc64(szFrame); + if( aFrame==0 ){ + rc = SQLITE_NOMEM_BKPT; + goto begin_unreliable_shm_out; + } + aData = &aFrame[WAL_FRAME_HDRSIZE]; + + /* Check to see if a complete transaction has been appended to the + ** wal file since the heap-memory wal-index was created. If so, the + ** heap-memory wal-index is discarded and WAL_RETRY returned to + ** the caller. */ + aSaveCksum[0] = pWal->hdr.aFrameCksum[0]; + aSaveCksum[1] = pWal->hdr.aFrameCksum[1]; + for(iOffset=walFrameOffset(pWal->hdr.mxFrame+1, pWal->szPage); + iOffset+szFrame<=szWal; + iOffset+=szFrame + ){ + u32 pgno; /* Database page number for frame */ + u32 nTruncate; /* dbsize field from frame header */ + + /* Read and decode the next log frame. */ + rc = sqlite3OsRead(pWal->pWalFd, aFrame, szFrame, iOffset); + if( rc!=SQLITE_OK ) break; + if( !walDecodeFrame(pWal, &pgno, &nTruncate, aData, aFrame) ) break; + + /* If nTruncate is non-zero, then a complete transaction has been + ** appended to this wal file. Set rc to WAL_RETRY and break out of + ** the loop. */ + if( nTruncate ){ + rc = WAL_RETRY; + break; + } + } + pWal->hdr.aFrameCksum[0] = aSaveCksum[0]; + pWal->hdr.aFrameCksum[1] = aSaveCksum[1]; + + begin_unreliable_shm_out: + sqlite3_free(aFrame); + if( rc!=SQLITE_OK ){ + int i; + for(i=0; i<pWal->nWiData; i++){ + sqlite3_free((void*)pWal->apWiData[i]); + pWal->apWiData[i] = 0; + } + pWal->bShmUnreliable = 0; + sqlite3WalEndReadTransaction(pWal); + *pChanged = 1; + } + return rc; +} + +/* +** Attempt to start a read transaction. This might fail due to a race or +** other transient condition. When that happens, it returns WAL_RETRY to +** indicate to the caller that it is safe to retry immediately. +** +** On success return SQLITE_OK. On a permanent failure (such an +** I/O error or an SQLITE_BUSY because another process is running +** recovery) return a positive error code. +** +** The useWal parameter is true to force the use of the WAL and disable +** the case where the WAL is bypassed because it has been completely +** checkpointed. If useWal==0 then this routine calls walIndexReadHdr() +** to make a copy of the wal-index header into pWal->hdr. If the +** wal-index header has changed, *pChanged is set to 1 (as an indication +** to the caller that the local page cache is obsolete and needs to be +** flushed.) When useWal==1, the wal-index header is assumed to already +** be loaded and the pChanged parameter is unused. +** +** The caller must set the cnt parameter to the number of prior calls to +** this routine during the current read attempt that returned WAL_RETRY. +** This routine will start taking more aggressive measures to clear the +** race conditions after multiple WAL_RETRY returns, and after an excessive +** number of errors will ultimately return SQLITE_PROTOCOL. The +** SQLITE_PROTOCOL return indicates that some other process has gone rogue +** and is not honoring the locking protocol. There is a vanishingly small +** chance that SQLITE_PROTOCOL could be returned because of a run of really +** bad luck when there is lots of contention for the wal-index, but that +** possibility is so small that it can be safely neglected, we believe. +** +** On success, this routine obtains a read lock on +** WAL_READ_LOCK(pWal->readLock). The pWal->readLock integer is +** in the range 0 <= pWal->readLock < WAL_NREADER. If pWal->readLock==(-1) +** that means the Wal does not hold any read lock. The reader must not +** access any database page that is modified by a WAL frame up to and +** including frame number aReadMark[pWal->readLock]. The reader will +** use WAL frames up to and including pWal->hdr.mxFrame if pWal->readLock>0 +** Or if pWal->readLock==0, then the reader will ignore the WAL +** completely and get all content directly from the database file. +** If the useWal parameter is 1 then the WAL will never be ignored and +** this routine will always set pWal->readLock>0 on success. +** When the read transaction is completed, the caller must release the +** lock on WAL_READ_LOCK(pWal->readLock) and set pWal->readLock to -1. +** +** This routine uses the nBackfill and aReadMark[] fields of the header +** to select a particular WAL_READ_LOCK() that strives to let the +** checkpoint process do as much work as possible. This routine might +** update values of the aReadMark[] array in the header, but if it does +** so it takes care to hold an exclusive lock on the corresponding +** WAL_READ_LOCK() while changing values. +*/ +static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){ + volatile WalCkptInfo *pInfo; /* Checkpoint information in wal-index */ + u32 mxReadMark; /* Largest aReadMark[] value */ + int mxI; /* Index of largest aReadMark[] value */ + int i; /* Loop counter */ + int rc = SQLITE_OK; /* Return code */ + u32 mxFrame; /* Wal frame to lock to */ + + assert( pWal->readLock<0 ); /* Not currently locked */ + + /* useWal may only be set for read/write connections */ + assert( (pWal->readOnly & WAL_SHM_RDONLY)==0 || useWal==0 ); + + /* Take steps to avoid spinning forever if there is a protocol error. + ** + ** Circumstances that cause a RETRY should only last for the briefest + ** instances of time. No I/O or other system calls are done while the + ** locks are held, so the locks should not be held for very long. But + ** if we are unlucky, another process that is holding a lock might get + ** paged out or take a page-fault that is time-consuming to resolve, + ** during the few nanoseconds that it is holding the lock. In that case, + ** it might take longer than normal for the lock to free. + ** + ** After 5 RETRYs, we begin calling sqlite3OsSleep(). The first few + ** calls to sqlite3OsSleep() have a delay of 1 microsecond. Really this + ** is more of a scheduler yield than an actual delay. But on the 10th + ** an subsequent retries, the delays start becoming longer and longer, + ** so that on the 100th (and last) RETRY we delay for 323 milliseconds. + ** The total delay time before giving up is less than 10 seconds. + */ + if( cnt>5 ){ + int nDelay = 1; /* Pause time in microseconds */ + if( cnt>100 ){ + VVA_ONLY( pWal->lockError = 1; ) + return SQLITE_PROTOCOL; + } + if( cnt>=10 ) nDelay = (cnt-9)*(cnt-9)*39; + sqlite3OsSleep(pWal->pVfs, nDelay); + } + + if( !useWal ){ + assert( rc==SQLITE_OK ); + if( pWal->bShmUnreliable==0 ){ + rc = walIndexReadHdr(pWal, pChanged); + } + if( rc==SQLITE_BUSY ){ + /* If there is not a recovery running in another thread or process + ** then convert BUSY errors to WAL_RETRY. If recovery is known to + ** be running, convert BUSY to BUSY_RECOVERY. There is a race here + ** which might cause WAL_RETRY to be returned even if BUSY_RECOVERY + ** would be technically correct. But the race is benign since with + ** WAL_RETRY this routine will be called again and will probably be + ** right on the second iteration. + */ + if( pWal->apWiData[0]==0 ){ + /* This branch is taken when the xShmMap() method returns SQLITE_BUSY. + ** We assume this is a transient condition, so return WAL_RETRY. The + ** xShmMap() implementation used by the default unix and win32 VFS + ** modules may return SQLITE_BUSY due to a race condition in the + ** code that determines whether or not the shared-memory region + ** must be zeroed before the requested page is returned. + */ + rc = WAL_RETRY; + }else if( SQLITE_OK==(rc = walLockShared(pWal, WAL_RECOVER_LOCK)) ){ + walUnlockShared(pWal, WAL_RECOVER_LOCK); + rc = WAL_RETRY; + }else if( rc==SQLITE_BUSY ){ + rc = SQLITE_BUSY_RECOVERY; + } + } + if( rc!=SQLITE_OK ){ + return rc; + } + else if( pWal->bShmUnreliable ){ + return walBeginShmUnreliable(pWal, pChanged); + } + } + + assert( pWal->nWiData>0 ); + assert( pWal->apWiData[0]!=0 ); + pInfo = walCkptInfo(pWal); + if( !useWal && AtomicLoad(&pInfo->nBackfill)==pWal->hdr.mxFrame +#ifdef SQLITE_ENABLE_SNAPSHOT + && (pWal->pSnapshot==0 || pWal->hdr.mxFrame==0) +#endif + ){ + /* The WAL has been completely backfilled (or it is empty). + ** and can be safely ignored. + */ + rc = walLockShared(pWal, WAL_READ_LOCK(0)); + walShmBarrier(pWal); + if( rc==SQLITE_OK ){ + if( memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) ){ + /* It is not safe to allow the reader to continue here if frames + ** may have been appended to the log before READ_LOCK(0) was obtained. + ** When holding READ_LOCK(0), the reader ignores the entire log file, + ** which implies that the database file contains a trustworthy + ** snapshot. Since holding READ_LOCK(0) prevents a checkpoint from + ** happening, this is usually correct. + ** + ** However, if frames have been appended to the log (or if the log + ** is wrapped and written for that matter) before the READ_LOCK(0) + ** is obtained, that is not necessarily true. A checkpointer may + ** have started to backfill the appended frames but crashed before + ** it finished. Leaving a corrupt image in the database file. + */ + walUnlockShared(pWal, WAL_READ_LOCK(0)); + return WAL_RETRY; + } + pWal->readLock = 0; + return SQLITE_OK; + }else if( rc!=SQLITE_BUSY ){ + return rc; + } + } + + /* If we get this far, it means that the reader will want to use + ** the WAL to get at content from recent commits. The job now is + ** to select one of the aReadMark[] entries that is closest to + ** but not exceeding pWal->hdr.mxFrame and lock that entry. + */ + mxReadMark = 0; + mxI = 0; + mxFrame = pWal->hdr.mxFrame; +#ifdef SQLITE_ENABLE_SNAPSHOT + if( pWal->pSnapshot && pWal->pSnapshot->mxFrame<mxFrame ){ + mxFrame = pWal->pSnapshot->mxFrame; + } +#endif + for(i=1; i<WAL_NREADER; i++){ + u32 thisMark = AtomicLoad(pInfo->aReadMark+i); + if( mxReadMark<=thisMark && thisMark<=mxFrame ){ + assert( thisMark!=READMARK_NOT_USED ); + mxReadMark = thisMark; + mxI = i; + } + } + if( (pWal->readOnly & WAL_SHM_RDONLY)==0 + && (mxReadMark<mxFrame || mxI==0) + ){ + for(i=1; i<WAL_NREADER; i++){ + rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1); + if( rc==SQLITE_OK ){ + AtomicStore(pInfo->aReadMark+i,mxFrame); + mxReadMark = mxFrame; + mxI = i; + walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1); + break; + }else if( rc!=SQLITE_BUSY ){ + return rc; + } + } + } + if( mxI==0 ){ + assert( rc==SQLITE_BUSY || (pWal->readOnly & WAL_SHM_RDONLY)!=0 ); + return rc==SQLITE_BUSY ? WAL_RETRY : SQLITE_READONLY_CANTINIT; + } + + rc = walLockShared(pWal, WAL_READ_LOCK(mxI)); + if( rc ){ + return rc==SQLITE_BUSY ? WAL_RETRY : rc; + } + /* Now that the read-lock has been obtained, check that neither the + ** value in the aReadMark[] array or the contents of the wal-index + ** header have changed. + ** + ** It is necessary to check that the wal-index header did not change + ** between the time it was read and when the shared-lock was obtained + ** on WAL_READ_LOCK(mxI) was obtained to account for the possibility + ** that the log file may have been wrapped by a writer, or that frames + ** that occur later in the log than pWal->hdr.mxFrame may have been + ** copied into the database by a checkpointer. If either of these things + ** happened, then reading the database with the current value of + ** pWal->hdr.mxFrame risks reading a corrupted snapshot. So, retry + ** instead. + ** + ** Before checking that the live wal-index header has not changed + ** since it was read, set Wal.minFrame to the first frame in the wal + ** file that has not yet been checkpointed. This client will not need + ** to read any frames earlier than minFrame from the wal file - they + ** can be safely read directly from the database file. + ** + ** Because a ShmBarrier() call is made between taking the copy of + ** nBackfill and checking that the wal-header in shared-memory still + ** matches the one cached in pWal->hdr, it is guaranteed that the + ** checkpointer that set nBackfill was not working with a wal-index + ** header newer than that cached in pWal->hdr. If it were, that could + ** cause a problem. The checkpointer could omit to checkpoint + ** a version of page X that lies before pWal->minFrame (call that version + ** A) on the basis that there is a newer version (version B) of the same + ** page later in the wal file. But if version B happens to like past + ** frame pWal->hdr.mxFrame - then the client would incorrectly assume + ** that it can read version A from the database file. However, since + ** we can guarantee that the checkpointer that set nBackfill could not + ** see any pages past pWal->hdr.mxFrame, this problem does not come up. + */ + pWal->minFrame = AtomicLoad(&pInfo->nBackfill)+1; + walShmBarrier(pWal); + if( AtomicLoad(pInfo->aReadMark+mxI)!=mxReadMark + || memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) + ){ + walUnlockShared(pWal, WAL_READ_LOCK(mxI)); + return WAL_RETRY; + }else{ + assert( mxReadMark<=pWal->hdr.mxFrame ); + pWal->readLock = (i16)mxI; + } + return rc; +} + +#ifdef SQLITE_ENABLE_SNAPSHOT +/* +** Attempt to reduce the value of the WalCkptInfo.nBackfillAttempted +** variable so that older snapshots can be accessed. To do this, loop +** through all wal frames from nBackfillAttempted to (nBackfill+1), +** comparing their content to the corresponding page with the database +** file, if any. Set nBackfillAttempted to the frame number of the +** first frame for which the wal file content matches the db file. +** +** This is only really safe if the file-system is such that any page +** writes made by earlier checkpointers were atomic operations, which +** is not always true. It is also possible that nBackfillAttempted +** may be left set to a value larger than expected, if a wal frame +** contains content that duplicate of an earlier version of the same +** page. +** +** SQLITE_OK is returned if successful, or an SQLite error code if an +** error occurs. It is not an error if nBackfillAttempted cannot be +** decreased at all. +*/ +int sqlite3WalSnapshotRecover(Wal *pWal){ + int rc; + + assert( pWal->readLock>=0 ); + rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1); + if( rc==SQLITE_OK ){ + volatile WalCkptInfo *pInfo = walCkptInfo(pWal); + int szPage = (int)pWal->szPage; + i64 szDb; /* Size of db file in bytes */ + + rc = sqlite3OsFileSize(pWal->pDbFd, &szDb); + if( rc==SQLITE_OK ){ + void *pBuf1 = sqlite3_malloc(szPage); + void *pBuf2 = sqlite3_malloc(szPage); + if( pBuf1==0 || pBuf2==0 ){ + rc = SQLITE_NOMEM; + }else{ + u32 i = pInfo->nBackfillAttempted; + for(i=pInfo->nBackfillAttempted; i>AtomicLoad(&pInfo->nBackfill); i--){ + WalHashLoc sLoc; /* Hash table location */ + u32 pgno; /* Page number in db file */ + i64 iDbOff; /* Offset of db file entry */ + i64 iWalOff; /* Offset of wal file entry */ + + rc = walHashGet(pWal, walFramePage(i), &sLoc); + if( rc!=SQLITE_OK ) break; + assert( i - sLoc.iZero - 1 >=0 ); + pgno = sLoc.aPgno[i-sLoc.iZero-1]; + iDbOff = (i64)(pgno-1) * szPage; + + if( iDbOff+szPage<=szDb ){ + iWalOff = walFrameOffset(i, szPage) + WAL_FRAME_HDRSIZE; + rc = sqlite3OsRead(pWal->pWalFd, pBuf1, szPage, iWalOff); + + if( rc==SQLITE_OK ){ + rc = sqlite3OsRead(pWal->pDbFd, pBuf2, szPage, iDbOff); + } + + if( rc!=SQLITE_OK || 0==memcmp(pBuf1, pBuf2, szPage) ){ + break; + } + } + + pInfo->nBackfillAttempted = i-1; + } + } + + sqlite3_free(pBuf1); + sqlite3_free(pBuf2); + } + walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1); + } + + return rc; +} +#endif /* SQLITE_ENABLE_SNAPSHOT */ + +/* +** Begin a read transaction on the database. +** +** This routine used to be called sqlite3OpenSnapshot() and with good reason: +** it takes a snapshot of the state of the WAL and wal-index for the current +** instant in time. The current thread will continue to use this snapshot. +** Other threads might append new content to the WAL and wal-index but +** that extra content is ignored by the current thread. +** +** If the database contents have changes since the previous read +** transaction, then *pChanged is set to 1 before returning. The +** Pager layer will use this to know that its cache is stale and +** needs to be flushed. +*/ +int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){ + int rc; /* Return code */ + int cnt = 0; /* Number of TryBeginRead attempts */ +#ifdef SQLITE_ENABLE_SNAPSHOT + int bChanged = 0; + WalIndexHdr *pSnapshot = pWal->pSnapshot; +#endif + + assert( pWal->ckptLock==0 ); + +#ifdef SQLITE_ENABLE_SNAPSHOT + if( pSnapshot ){ + if( memcmp(pSnapshot, &pWal->hdr, sizeof(WalIndexHdr))!=0 ){ + bChanged = 1; + } + + /* It is possible that there is a checkpointer thread running + ** concurrent with this code. If this is the case, it may be that the + ** checkpointer has already determined that it will checkpoint + ** snapshot X, where X is later in the wal file than pSnapshot, but + ** has not yet set the pInfo->nBackfillAttempted variable to indicate + ** its intent. To avoid the race condition this leads to, ensure that + ** there is no checkpointer process by taking a shared CKPT lock + ** before checking pInfo->nBackfillAttempted. */ + (void)walEnableBlocking(pWal); + rc = walLockShared(pWal, WAL_CKPT_LOCK); + walDisableBlocking(pWal); + + if( rc!=SQLITE_OK ){ + return rc; + } + pWal->ckptLock = 1; + } +#endif + + do{ + rc = walTryBeginRead(pWal, pChanged, 0, ++cnt); + }while( rc==WAL_RETRY ); + testcase( (rc&0xff)==SQLITE_BUSY ); + testcase( (rc&0xff)==SQLITE_IOERR ); + testcase( rc==SQLITE_PROTOCOL ); + testcase( rc==SQLITE_OK ); + +#ifdef SQLITE_ENABLE_SNAPSHOT + if( rc==SQLITE_OK ){ + if( pSnapshot && memcmp(pSnapshot, &pWal->hdr, sizeof(WalIndexHdr))!=0 ){ + /* At this point the client has a lock on an aReadMark[] slot holding + ** a value equal to or smaller than pSnapshot->mxFrame, but pWal->hdr + ** is populated with the wal-index header corresponding to the head + ** of the wal file. Verify that pSnapshot is still valid before + ** continuing. Reasons why pSnapshot might no longer be valid: + ** + ** (1) The WAL file has been reset since the snapshot was taken. + ** In this case, the salt will have changed. + ** + ** (2) A checkpoint as been attempted that wrote frames past + ** pSnapshot->mxFrame into the database file. Note that the + ** checkpoint need not have completed for this to cause problems. + */ + volatile WalCkptInfo *pInfo = walCkptInfo(pWal); + + assert( pWal->readLock>0 || pWal->hdr.mxFrame==0 ); + assert( pInfo->aReadMark[pWal->readLock]<=pSnapshot->mxFrame ); + + /* Check that the wal file has not been wrapped. Assuming that it has + ** not, also check that no checkpointer has attempted to checkpoint any + ** frames beyond pSnapshot->mxFrame. If either of these conditions are + ** true, return SQLITE_ERROR_SNAPSHOT. Otherwise, overwrite pWal->hdr + ** with *pSnapshot and set *pChanged as appropriate for opening the + ** snapshot. */ + if( !memcmp(pSnapshot->aSalt, pWal->hdr.aSalt, sizeof(pWal->hdr.aSalt)) + && pSnapshot->mxFrame>=pInfo->nBackfillAttempted + ){ + assert( pWal->readLock>0 ); + memcpy(&pWal->hdr, pSnapshot, sizeof(WalIndexHdr)); + *pChanged = bChanged; + }else{ + rc = SQLITE_ERROR_SNAPSHOT; + } + + /* A client using a non-current snapshot may not ignore any frames + ** from the start of the wal file. This is because, for a system + ** where (minFrame < iSnapshot < maxFrame), a checkpointer may + ** have omitted to checkpoint a frame earlier than minFrame in + ** the file because there exists a frame after iSnapshot that + ** is the same database page. */ + pWal->minFrame = 1; + + if( rc!=SQLITE_OK ){ + sqlite3WalEndReadTransaction(pWal); + } + } + } + + /* Release the shared CKPT lock obtained above. */ + if( pWal->ckptLock ){ + assert( pSnapshot ); + walUnlockShared(pWal, WAL_CKPT_LOCK); + pWal->ckptLock = 0; + } +#endif + return rc; +} + +/* +** Finish with a read transaction. All this does is release the +** read-lock. +*/ +void sqlite3WalEndReadTransaction(Wal *pWal){ + sqlite3WalEndWriteTransaction(pWal); + if( pWal->readLock>=0 ){ + walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock)); + pWal->readLock = -1; + } +} + +/* +** Search the wal file for page pgno. If found, set *piRead to the frame that +** contains the page. Otherwise, if pgno is not in the wal file, set *piRead +** to zero. +** +** Return SQLITE_OK if successful, or an error code if an error occurs. If an +** error does occur, the final value of *piRead is undefined. +*/ +int sqlite3WalFindFrame( + Wal *pWal, /* WAL handle */ + Pgno pgno, /* Database page number to read data for */ + u32 *piRead /* OUT: Frame number (or zero) */ +){ + u32 iRead = 0; /* If !=0, WAL frame to return data from */ + u32 iLast = pWal->hdr.mxFrame; /* Last page in WAL for this reader */ + int iHash; /* Used to loop through N hash tables */ + int iMinHash; + + /* This routine is only be called from within a read transaction. */ + assert( pWal->readLock>=0 || pWal->lockError ); + + /* If the "last page" field of the wal-index header snapshot is 0, then + ** no data will be read from the wal under any circumstances. Return early + ** in this case as an optimization. Likewise, if pWal->readLock==0, + ** then the WAL is ignored by the reader so return early, as if the + ** WAL were empty. + */ + if( iLast==0 || (pWal->readLock==0 && pWal->bShmUnreliable==0) ){ + *piRead = 0; + return SQLITE_OK; + } + + /* Search the hash table or tables for an entry matching page number + ** pgno. Each iteration of the following for() loop searches one + ** hash table (each hash table indexes up to HASHTABLE_NPAGE frames). + ** + ** This code might run concurrently to the code in walIndexAppend() + ** that adds entries to the wal-index (and possibly to this hash + ** table). This means the value just read from the hash + ** slot (aHash[iKey]) may have been added before or after the + ** current read transaction was opened. Values added after the + ** read transaction was opened may have been written incorrectly - + ** i.e. these slots may contain garbage data. However, we assume + ** that any slots written before the current read transaction was + ** opened remain unmodified. + ** + ** For the reasons above, the if(...) condition featured in the inner + ** loop of the following block is more stringent that would be required + ** if we had exclusive access to the hash-table: + ** + ** (aPgno[iFrame]==pgno): + ** This condition filters out normal hash-table collisions. + ** + ** (iFrame<=iLast): + ** This condition filters out entries that were added to the hash + ** table after the current read-transaction had started. + */ + iMinHash = walFramePage(pWal->minFrame); + for(iHash=walFramePage(iLast); iHash>=iMinHash; iHash--){ + WalHashLoc sLoc; /* Hash table location */ + int iKey; /* Hash slot index */ + int nCollide; /* Number of hash collisions remaining */ + int rc; /* Error code */ + u32 iH; + + rc = walHashGet(pWal, iHash, &sLoc); + if( rc!=SQLITE_OK ){ + return rc; + } + nCollide = HASHTABLE_NSLOT; + iKey = walHash(pgno); + while( (iH = AtomicLoad(&sLoc.aHash[iKey]))!=0 ){ + u32 iFrame = iH + sLoc.iZero; + if( iFrame<=iLast && iFrame>=pWal->minFrame && sLoc.aPgno[iH-1]==pgno ){ + assert( iFrame>iRead || CORRUPT_DB ); + iRead = iFrame; + } + if( (nCollide--)==0 ){ + return SQLITE_CORRUPT_BKPT; + } + iKey = walNextHash(iKey); + } + if( iRead ) break; + } + +#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT + /* If expensive assert() statements are available, do a linear search + ** of the wal-index file content. Make sure the results agree with the + ** result obtained using the hash indexes above. */ + { + u32 iRead2 = 0; + u32 iTest; + assert( pWal->bShmUnreliable || pWal->minFrame>0 ); + for(iTest=iLast; iTest>=pWal->minFrame && iTest>0; iTest--){ + if( walFramePgno(pWal, iTest)==pgno ){ + iRead2 = iTest; + break; + } + } + assert( iRead==iRead2 ); + } +#endif + + *piRead = iRead; + return SQLITE_OK; +} + +/* +** Read the contents of frame iRead from the wal file into buffer pOut +** (which is nOut bytes in size). Return SQLITE_OK if successful, or an +** error code otherwise. +*/ +int sqlite3WalReadFrame( + Wal *pWal, /* WAL handle */ + u32 iRead, /* Frame to read */ + int nOut, /* Size of buffer pOut in bytes */ + u8 *pOut /* Buffer to write page data to */ +){ + int sz; + i64 iOffset; + sz = pWal->hdr.szPage; + sz = (sz&0xfe00) + ((sz&0x0001)<<16); + testcase( sz<=32768 ); + testcase( sz>=65536 ); + iOffset = walFrameOffset(iRead, sz) + WAL_FRAME_HDRSIZE; + /* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL */ + return sqlite3OsRead(pWal->pWalFd, pOut, (nOut>sz ? sz : nOut), iOffset); +} + +/* +** Return the size of the database in pages (or zero, if unknown). +*/ +Pgno sqlite3WalDbsize(Wal *pWal){ + if( pWal && ALWAYS(pWal->readLock>=0) ){ + return pWal->hdr.nPage; + } + return 0; +} + + +/* +** This function starts a write transaction on the WAL. +** +** A read transaction must have already been started by a prior call +** to sqlite3WalBeginReadTransaction(). +** +** If another thread or process has written into the database since +** the read transaction was started, then it is not possible for this +** thread to write as doing so would cause a fork. So this routine +** returns SQLITE_BUSY in that case and no write transaction is started. +** +** There can only be a single writer active at a time. +*/ +int sqlite3WalBeginWriteTransaction(Wal *pWal){ + int rc; + +#ifdef SQLITE_ENABLE_SETLK_TIMEOUT + /* If the write-lock is already held, then it was obtained before the + ** read-transaction was even opened, making this call a no-op. + ** Return early. */ + if( pWal->writeLock ){ + assert( !memcmp(&pWal->hdr,(void *)walIndexHdr(pWal),sizeof(WalIndexHdr)) ); + return SQLITE_OK; + } +#endif + + /* Cannot start a write transaction without first holding a read + ** transaction. */ + assert( pWal->readLock>=0 ); + assert( pWal->writeLock==0 && pWal->iReCksum==0 ); + + if( pWal->readOnly ){ + return SQLITE_READONLY; + } + + /* Only one writer allowed at a time. Get the write lock. Return + ** SQLITE_BUSY if unable. + */ + rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1); + if( rc ){ + return rc; + } + pWal->writeLock = 1; + + /* If another connection has written to the database file since the + ** time the read transaction on this connection was started, then + ** the write is disallowed. + */ + if( memcmp(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr))!=0 ){ + walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1); + pWal->writeLock = 0; + rc = SQLITE_BUSY_SNAPSHOT; + } + + return rc; +} + +/* +** End a write transaction. The commit has already been done. This +** routine merely releases the lock. +*/ +int sqlite3WalEndWriteTransaction(Wal *pWal){ + if( pWal->writeLock ){ + walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1); + pWal->writeLock = 0; + pWal->iReCksum = 0; + pWal->truncateOnCommit = 0; + } + return SQLITE_OK; +} + +/* +** If any data has been written (but not committed) to the log file, this +** function moves the write-pointer back to the start of the transaction. +** +** Additionally, the callback function is invoked for each frame written +** to the WAL since the start of the transaction. If the callback returns +** other than SQLITE_OK, it is not invoked again and the error code is +** returned to the caller. +** +** Otherwise, if the callback function does not return an error, this +** function returns SQLITE_OK. +*/ +int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx){ + int rc = SQLITE_OK; + if( ALWAYS(pWal->writeLock) ){ + Pgno iMax = pWal->hdr.mxFrame; + Pgno iFrame; + + /* Restore the clients cache of the wal-index header to the state it + ** was in before the client began writing to the database. + */ + memcpy(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr)); + + for(iFrame=pWal->hdr.mxFrame+1; + ALWAYS(rc==SQLITE_OK) && iFrame<=iMax; + iFrame++ + ){ + /* This call cannot fail. Unless the page for which the page number + ** is passed as the second argument is (a) in the cache and + ** (b) has an outstanding reference, then xUndo is either a no-op + ** (if (a) is false) or simply expels the page from the cache (if (b) + ** is false). + ** + ** If the upper layer is doing a rollback, it is guaranteed that there + ** are no outstanding references to any page other than page 1. And + ** page 1 is never written to the log until the transaction is + ** committed. As a result, the call to xUndo may not fail. + */ + assert( walFramePgno(pWal, iFrame)!=1 ); + rc = xUndo(pUndoCtx, walFramePgno(pWal, iFrame)); + } + if( iMax!=pWal->hdr.mxFrame ) walCleanupHash(pWal); + } + return rc; +} + +/* +** Argument aWalData must point to an array of WAL_SAVEPOINT_NDATA u32 +** values. This function populates the array with values required to +** "rollback" the write position of the WAL handle back to the current +** point in the event of a savepoint rollback (via WalSavepointUndo()). +*/ +void sqlite3WalSavepoint(Wal *pWal, u32 *aWalData){ + assert( pWal->writeLock ); + aWalData[0] = pWal->hdr.mxFrame; + aWalData[1] = pWal->hdr.aFrameCksum[0]; + aWalData[2] = pWal->hdr.aFrameCksum[1]; + aWalData[3] = pWal->nCkpt; +} + +/* +** Move the write position of the WAL back to the point identified by +** the values in the aWalData[] array. aWalData must point to an array +** of WAL_SAVEPOINT_NDATA u32 values that has been previously populated +** by a call to WalSavepoint(). +*/ +int sqlite3WalSavepointUndo(Wal *pWal, u32 *aWalData){ + int rc = SQLITE_OK; + + assert( pWal->writeLock ); + assert( aWalData[3]!=pWal->nCkpt || aWalData[0]<=pWal->hdr.mxFrame ); + + if( aWalData[3]!=pWal->nCkpt ){ + /* This savepoint was opened immediately after the write-transaction + ** was started. Right after that, the writer decided to wrap around + ** to the start of the log. Update the savepoint values to match. + */ + aWalData[0] = 0; + aWalData[3] = pWal->nCkpt; + } + + if( aWalData[0]<pWal->hdr.mxFrame ){ + pWal->hdr.mxFrame = aWalData[0]; + pWal->hdr.aFrameCksum[0] = aWalData[1]; + pWal->hdr.aFrameCksum[1] = aWalData[2]; + walCleanupHash(pWal); + } + + return rc; +} + +/* +** This function is called just before writing a set of frames to the log +** file (see sqlite3WalFrames()). It checks to see if, instead of appending +** to the current log file, it is possible to overwrite the start of the +** existing log file with the new frames (i.e. "reset" the log). If so, +** it sets pWal->hdr.mxFrame to 0. Otherwise, pWal->hdr.mxFrame is left +** unchanged. +** +** SQLITE_OK is returned if no error is encountered (regardless of whether +** or not pWal->hdr.mxFrame is modified). An SQLite error code is returned +** if an error occurs. +*/ +static int walRestartLog(Wal *pWal){ + int rc = SQLITE_OK; + int cnt; + + if( pWal->readLock==0 ){ + volatile WalCkptInfo *pInfo = walCkptInfo(pWal); + assert( pInfo->nBackfill==pWal->hdr.mxFrame ); + if( pInfo->nBackfill>0 ){ + u32 salt1; + sqlite3_randomness(4, &salt1); + rc = walLockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1); + if( rc==SQLITE_OK ){ + /* If all readers are using WAL_READ_LOCK(0) (in other words if no + ** readers are currently using the WAL), then the transactions + ** frames will overwrite the start of the existing log. Update the + ** wal-index header to reflect this. + ** + ** In theory it would be Ok to update the cache of the header only + ** at this point. But updating the actual wal-index header is also + ** safe and means there is no special case for sqlite3WalUndo() + ** to handle if this transaction is rolled back. */ + walRestartHdr(pWal, salt1); + walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1); + }else if( rc!=SQLITE_BUSY ){ + return rc; + } + } + walUnlockShared(pWal, WAL_READ_LOCK(0)); + pWal->readLock = -1; + cnt = 0; + do{ + int notUsed; + rc = walTryBeginRead(pWal, ¬Used, 1, ++cnt); + }while( rc==WAL_RETRY ); + assert( (rc&0xff)!=SQLITE_BUSY ); /* BUSY not possible when useWal==1 */ + testcase( (rc&0xff)==SQLITE_IOERR ); + testcase( rc==SQLITE_PROTOCOL ); + testcase( rc==SQLITE_OK ); + } + return rc; +} + +/* +** Information about the current state of the WAL file and where +** the next fsync should occur - passed from sqlite3WalFrames() into +** walWriteToLog(). +*/ +typedef struct WalWriter { + Wal *pWal; /* The complete WAL information */ + sqlite3_file *pFd; /* The WAL file to which we write */ + sqlite3_int64 iSyncPoint; /* Fsync at this offset */ + int syncFlags; /* Flags for the fsync */ + int szPage; /* Size of one page */ +} WalWriter; + +/* +** Write iAmt bytes of content into the WAL file beginning at iOffset. +** Do a sync when crossing the p->iSyncPoint boundary. +** +** In other words, if iSyncPoint is in between iOffset and iOffset+iAmt, +** first write the part before iSyncPoint, then sync, then write the +** rest. +*/ +static int walWriteToLog( + WalWriter *p, /* WAL to write to */ + void *pContent, /* Content to be written */ + int iAmt, /* Number of bytes to write */ + sqlite3_int64 iOffset /* Start writing at this offset */ +){ + int rc; + if( iOffset<p->iSyncPoint && iOffset+iAmt>=p->iSyncPoint ){ + int iFirstAmt = (int)(p->iSyncPoint - iOffset); + rc = sqlite3OsWrite(p->pFd, pContent, iFirstAmt, iOffset); + if( rc ) return rc; + iOffset += iFirstAmt; + iAmt -= iFirstAmt; + pContent = (void*)(iFirstAmt + (char*)pContent); + assert( WAL_SYNC_FLAGS(p->syncFlags)!=0 ); + rc = sqlite3OsSync(p->pFd, WAL_SYNC_FLAGS(p->syncFlags)); + if( iAmt==0 || rc ) return rc; + } + rc = sqlite3OsWrite(p->pFd, pContent, iAmt, iOffset); + return rc; +} + +/* +** Write out a single frame of the WAL +*/ +static int walWriteOneFrame( + WalWriter *p, /* Where to write the frame */ + PgHdr *pPage, /* The page of the frame to be written */ + int nTruncate, /* The commit flag. Usually 0. >0 for commit */ + sqlite3_int64 iOffset /* Byte offset at which to write */ +){ + int rc; /* Result code from subfunctions */ + void *pData; /* Data actually written */ + u8 aFrame[WAL_FRAME_HDRSIZE]; /* Buffer to assemble frame-header in */ + pData = pPage->pData; + walEncodeFrame(p->pWal, pPage->pgno, nTruncate, pData, aFrame); + rc = walWriteToLog(p, aFrame, sizeof(aFrame), iOffset); + if( rc ) return rc; + /* Write the page data */ + rc = walWriteToLog(p, pData, p->szPage, iOffset+sizeof(aFrame)); + return rc; +} + +/* +** This function is called as part of committing a transaction within which +** one or more frames have been overwritten. It updates the checksums for +** all frames written to the wal file by the current transaction starting +** with the earliest to have been overwritten. +** +** SQLITE_OK is returned if successful, or an SQLite error code otherwise. +*/ +static int walRewriteChecksums(Wal *pWal, u32 iLast){ + const int szPage = pWal->szPage;/* Database page size */ + int rc = SQLITE_OK; /* Return code */ + u8 *aBuf; /* Buffer to load data from wal file into */ + u8 aFrame[WAL_FRAME_HDRSIZE]; /* Buffer to assemble frame-headers in */ + u32 iRead; /* Next frame to read from wal file */ + i64 iCksumOff; + + aBuf = sqlite3_malloc(szPage + WAL_FRAME_HDRSIZE); + if( aBuf==0 ) return SQLITE_NOMEM_BKPT; + + /* Find the checksum values to use as input for the recalculating the + ** first checksum. If the first frame is frame 1 (implying that the current + ** transaction restarted the wal file), these values must be read from the + ** wal-file header. Otherwise, read them from the frame header of the + ** previous frame. */ + assert( pWal->iReCksum>0 ); + if( pWal->iReCksum==1 ){ + iCksumOff = 24; + }else{ + iCksumOff = walFrameOffset(pWal->iReCksum-1, szPage) + 16; + } + rc = sqlite3OsRead(pWal->pWalFd, aBuf, sizeof(u32)*2, iCksumOff); + pWal->hdr.aFrameCksum[0] = sqlite3Get4byte(aBuf); + pWal->hdr.aFrameCksum[1] = sqlite3Get4byte(&aBuf[sizeof(u32)]); + + iRead = pWal->iReCksum; + pWal->iReCksum = 0; + for(; rc==SQLITE_OK && iRead<=iLast; iRead++){ + i64 iOff = walFrameOffset(iRead, szPage); + rc = sqlite3OsRead(pWal->pWalFd, aBuf, szPage+WAL_FRAME_HDRSIZE, iOff); + if( rc==SQLITE_OK ){ + u32 iPgno, nDbSize; + iPgno = sqlite3Get4byte(aBuf); + nDbSize = sqlite3Get4byte(&aBuf[4]); + + walEncodeFrame(pWal, iPgno, nDbSize, &aBuf[WAL_FRAME_HDRSIZE], aFrame); + rc = sqlite3OsWrite(pWal->pWalFd, aFrame, sizeof(aFrame), iOff); + } + } + + sqlite3_free(aBuf); + return rc; +} + +/* +** Write a set of frames to the log. The caller must hold the write-lock +** on the log file (obtained using sqlite3WalBeginWriteTransaction()). +*/ +int sqlite3WalFrames( + Wal *pWal, /* Wal handle to write to */ + int szPage, /* Database page-size in bytes */ + PgHdr *pList, /* List of dirty pages to write */ + Pgno nTruncate, /* Database size after this commit */ + int isCommit, /* True if this is a commit */ + int sync_flags /* Flags to pass to OsSync() (or 0) */ +){ + int rc; /* Used to catch return codes */ + u32 iFrame; /* Next frame address */ + PgHdr *p; /* Iterator to run through pList with. */ + PgHdr *pLast = 0; /* Last frame in list */ + int nExtra = 0; /* Number of extra copies of last page */ + int szFrame; /* The size of a single frame */ + i64 iOffset; /* Next byte to write in WAL file */ + WalWriter w; /* The writer */ + u32 iFirst = 0; /* First frame that may be overwritten */ + WalIndexHdr *pLive; /* Pointer to shared header */ + + assert( pList ); + assert( pWal->writeLock ); + + /* If this frame set completes a transaction, then nTruncate>0. If + ** nTruncate==0 then this frame set does not complete the transaction. */ + assert( (isCommit!=0)==(nTruncate!=0) ); + +#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG) + { int cnt; for(cnt=0, p=pList; p; p=p->pDirty, cnt++){} + WALTRACE(("WAL%p: frame write begin. %d frames. mxFrame=%d. %s\n", + pWal, cnt, pWal->hdr.mxFrame, isCommit ? "Commit" : "Spill")); + } +#endif + + pLive = (WalIndexHdr*)walIndexHdr(pWal); + if( memcmp(&pWal->hdr, (void *)pLive, sizeof(WalIndexHdr))!=0 ){ + iFirst = pLive->mxFrame+1; + } + + /* See if it is possible to write these frames into the start of the + ** log file, instead of appending to it at pWal->hdr.mxFrame. + */ + if( SQLITE_OK!=(rc = walRestartLog(pWal)) ){ + return rc; + } + + /* If this is the first frame written into the log, write the WAL + ** header to the start of the WAL file. See comments at the top of + ** this source file for a description of the WAL header format. + */ + iFrame = pWal->hdr.mxFrame; + if( iFrame==0 ){ + u8 aWalHdr[WAL_HDRSIZE]; /* Buffer to assemble wal-header in */ + u32 aCksum[2]; /* Checksum for wal-header */ + + sqlite3Put4byte(&aWalHdr[0], (WAL_MAGIC | SQLITE_BIGENDIAN)); + sqlite3Put4byte(&aWalHdr[4], WAL_MAX_VERSION); + sqlite3Put4byte(&aWalHdr[8], szPage); + sqlite3Put4byte(&aWalHdr[12], pWal->nCkpt); + if( pWal->nCkpt==0 ) sqlite3_randomness(8, pWal->hdr.aSalt); + memcpy(&aWalHdr[16], pWal->hdr.aSalt, 8); + walChecksumBytes(1, aWalHdr, WAL_HDRSIZE-2*4, 0, aCksum); + sqlite3Put4byte(&aWalHdr[24], aCksum[0]); + sqlite3Put4byte(&aWalHdr[28], aCksum[1]); + + pWal->szPage = szPage; + pWal->hdr.bigEndCksum = SQLITE_BIGENDIAN; + pWal->hdr.aFrameCksum[0] = aCksum[0]; + pWal->hdr.aFrameCksum[1] = aCksum[1]; + pWal->truncateOnCommit = 1; + + rc = sqlite3OsWrite(pWal->pWalFd, aWalHdr, sizeof(aWalHdr), 0); + WALTRACE(("WAL%p: wal-header write %s\n", pWal, rc ? "failed" : "ok")); + if( rc!=SQLITE_OK ){ + return rc; + } + + /* Sync the header (unless SQLITE_IOCAP_SEQUENTIAL is true or unless + ** all syncing is turned off by PRAGMA synchronous=OFF). Otherwise + ** an out-of-order write following a WAL restart could result in + ** database corruption. See the ticket: + ** + ** https://sqlite.org/src/info/ff5be73dee + */ + if( pWal->syncHeader ){ + rc = sqlite3OsSync(pWal->pWalFd, CKPT_SYNC_FLAGS(sync_flags)); + if( rc ) return rc; + } + } + assert( (int)pWal->szPage==szPage ); + + /* Setup information needed to write frames into the WAL */ + w.pWal = pWal; + w.pFd = pWal->pWalFd; + w.iSyncPoint = 0; + w.syncFlags = sync_flags; + w.szPage = szPage; + iOffset = walFrameOffset(iFrame+1, szPage); + szFrame = szPage + WAL_FRAME_HDRSIZE; + + /* Write all frames into the log file exactly once */ + for(p=pList; p; p=p->pDirty){ + int nDbSize; /* 0 normally. Positive == commit flag */ + + /* Check if this page has already been written into the wal file by + ** the current transaction. If so, overwrite the existing frame and + ** set Wal.writeLock to WAL_WRITELOCK_RECKSUM - indicating that + ** checksums must be recomputed when the transaction is committed. */ + if( iFirst && (p->pDirty || isCommit==0) ){ + u32 iWrite = 0; + VVA_ONLY(rc =) sqlite3WalFindFrame(pWal, p->pgno, &iWrite); + assert( rc==SQLITE_OK || iWrite==0 ); + if( iWrite>=iFirst ){ + i64 iOff = walFrameOffset(iWrite, szPage) + WAL_FRAME_HDRSIZE; + void *pData; + if( pWal->iReCksum==0 || iWrite<pWal->iReCksum ){ + pWal->iReCksum = iWrite; + } + pData = p->pData; + rc = sqlite3OsWrite(pWal->pWalFd, pData, szPage, iOff); + if( rc ) return rc; + p->flags &= ~PGHDR_WAL_APPEND; + continue; + } + } + + iFrame++; + assert( iOffset==walFrameOffset(iFrame, szPage) ); + nDbSize = (isCommit && p->pDirty==0) ? nTruncate : 0; + rc = walWriteOneFrame(&w, p, nDbSize, iOffset); + if( rc ) return rc; + pLast = p; + iOffset += szFrame; + p->flags |= PGHDR_WAL_APPEND; + } + + /* Recalculate checksums within the wal file if required. */ + if( isCommit && pWal->iReCksum ){ + rc = walRewriteChecksums(pWal, iFrame); + if( rc ) return rc; + } + + /* If this is the end of a transaction, then we might need to pad + ** the transaction and/or sync the WAL file. + ** + ** Padding and syncing only occur if this set of frames complete a + ** transaction and if PRAGMA synchronous=FULL. If synchronous==NORMAL + ** or synchronous==OFF, then no padding or syncing are needed. + ** + ** If SQLITE_IOCAP_POWERSAFE_OVERWRITE is defined, then padding is not + ** needed and only the sync is done. If padding is needed, then the + ** final frame is repeated (with its commit mark) until the next sector + ** boundary is crossed. Only the part of the WAL prior to the last + ** sector boundary is synced; the part of the last frame that extends + ** past the sector boundary is written after the sync. + */ + if( isCommit && WAL_SYNC_FLAGS(sync_flags)!=0 ){ + int bSync = 1; + if( pWal->padToSectorBoundary ){ + int sectorSize = sqlite3SectorSize(pWal->pWalFd); + w.iSyncPoint = ((iOffset+sectorSize-1)/sectorSize)*sectorSize; + bSync = (w.iSyncPoint==iOffset); + testcase( bSync ); + while( iOffset<w.iSyncPoint ){ + rc = walWriteOneFrame(&w, pLast, nTruncate, iOffset); + if( rc ) return rc; + iOffset += szFrame; + nExtra++; + assert( pLast!=0 ); + } + } + if( bSync ){ + assert( rc==SQLITE_OK ); + rc = sqlite3OsSync(w.pFd, WAL_SYNC_FLAGS(sync_flags)); + } + } + + /* If this frame set completes the first transaction in the WAL and + ** if PRAGMA journal_size_limit is set, then truncate the WAL to the + ** journal size limit, if possible. + */ + if( isCommit && pWal->truncateOnCommit && pWal->mxWalSize>=0 ){ + i64 sz = pWal->mxWalSize; + if( walFrameOffset(iFrame+nExtra+1, szPage)>pWal->mxWalSize ){ + sz = walFrameOffset(iFrame+nExtra+1, szPage); + } + walLimitSize(pWal, sz); + pWal->truncateOnCommit = 0; + } + + /* Append data to the wal-index. It is not necessary to lock the + ** wal-index to do this as the SQLITE_SHM_WRITE lock held on the wal-index + ** guarantees that there are no other writers, and no data that may + ** be in use by existing readers is being overwritten. + */ + iFrame = pWal->hdr.mxFrame; + for(p=pList; p && rc==SQLITE_OK; p=p->pDirty){ + if( (p->flags & PGHDR_WAL_APPEND)==0 ) continue; + iFrame++; + rc = walIndexAppend(pWal, iFrame, p->pgno); + } + assert( pLast!=0 || nExtra==0 ); + while( rc==SQLITE_OK && nExtra>0 ){ + iFrame++; + nExtra--; + rc = walIndexAppend(pWal, iFrame, pLast->pgno); + } + + if( rc==SQLITE_OK ){ + /* Update the private copy of the header. */ + pWal->hdr.szPage = (u16)((szPage&0xff00) | (szPage>>16)); + testcase( szPage<=32768 ); + testcase( szPage>=65536 ); + pWal->hdr.mxFrame = iFrame; + if( isCommit ){ + pWal->hdr.iChange++; + pWal->hdr.nPage = nTruncate; + } + /* If this is a commit, update the wal-index header too. */ + if( isCommit ){ + walIndexWriteHdr(pWal); + pWal->iCallback = iFrame; + } + } + + WALTRACE(("WAL%p: frame write %s\n", pWal, rc ? "failed" : "ok")); + return rc; +} + +/* +** This routine is called to implement sqlite3_wal_checkpoint() and +** related interfaces. +** +** Obtain a CHECKPOINT lock and then backfill as much information as +** we can from WAL into the database. +** +** If parameter xBusy is not NULL, it is a pointer to a busy-handler +** callback. In this case this function runs a blocking checkpoint. +*/ +int sqlite3WalCheckpoint( + Wal *pWal, /* Wal connection */ + sqlite3 *db, /* Check this handle's interrupt flag */ + int eMode, /* PASSIVE, FULL, RESTART, or TRUNCATE */ + int (*xBusy)(void*), /* Function to call when busy */ + void *pBusyArg, /* Context argument for xBusyHandler */ + int sync_flags, /* Flags to sync db file with (or 0) */ + int nBuf, /* Size of temporary buffer */ + u8 *zBuf, /* Temporary buffer to use */ + int *pnLog, /* OUT: Number of frames in WAL */ + int *pnCkpt /* OUT: Number of backfilled frames in WAL */ +){ + int rc; /* Return code */ + int isChanged = 0; /* True if a new wal-index header is loaded */ + int eMode2 = eMode; /* Mode to pass to walCheckpoint() */ + int (*xBusy2)(void*) = xBusy; /* Busy handler for eMode2 */ + + assert( pWal->ckptLock==0 ); + assert( pWal->writeLock==0 ); + + /* EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked + ** in the SQLITE_CHECKPOINT_PASSIVE mode. */ + assert( eMode!=SQLITE_CHECKPOINT_PASSIVE || xBusy==0 ); + + if( pWal->readOnly ) return SQLITE_READONLY; + WALTRACE(("WAL%p: checkpoint begins\n", pWal)); + + /* Enable blocking locks, if possible. If blocking locks are successfully + ** enabled, set xBusy2=0 so that the busy-handler is never invoked. */ + sqlite3WalDb(pWal, db); + (void)walEnableBlocking(pWal); + + /* IMPLEMENTATION-OF: R-62028-47212 All calls obtain an exclusive + ** "checkpoint" lock on the database file. + ** EVIDENCE-OF: R-10421-19736 If any other process is running a + ** checkpoint operation at the same time, the lock cannot be obtained and + ** SQLITE_BUSY is returned. + ** EVIDENCE-OF: R-53820-33897 Even if there is a busy-handler configured, + ** it will not be invoked in this case. + */ + rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1); + testcase( rc==SQLITE_BUSY ); + testcase( rc!=SQLITE_OK && xBusy2!=0 ); + if( rc==SQLITE_OK ){ + pWal->ckptLock = 1; + + /* IMPLEMENTATION-OF: R-59782-36818 The SQLITE_CHECKPOINT_FULL, RESTART and + ** TRUNCATE modes also obtain the exclusive "writer" lock on the database + ** file. + ** + ** EVIDENCE-OF: R-60642-04082 If the writer lock cannot be obtained + ** immediately, and a busy-handler is configured, it is invoked and the + ** writer lock retried until either the busy-handler returns 0 or the + ** lock is successfully obtained. + */ + if( eMode!=SQLITE_CHECKPOINT_PASSIVE ){ + rc = walBusyLock(pWal, xBusy2, pBusyArg, WAL_WRITE_LOCK, 1); + if( rc==SQLITE_OK ){ + pWal->writeLock = 1; + }else if( rc==SQLITE_BUSY ){ + eMode2 = SQLITE_CHECKPOINT_PASSIVE; + xBusy2 = 0; + rc = SQLITE_OK; + } + } + } + + + /* Read the wal-index header. */ + if( rc==SQLITE_OK ){ + walDisableBlocking(pWal); + rc = walIndexReadHdr(pWal, &isChanged); + (void)walEnableBlocking(pWal); + if( isChanged && pWal->pDbFd->pMethods->iVersion>=3 ){ + sqlite3OsUnfetch(pWal->pDbFd, 0, 0); + } + } + + /* Copy data from the log to the database file. */ + if( rc==SQLITE_OK ){ + + if( pWal->hdr.mxFrame && walPagesize(pWal)!=nBuf ){ + rc = SQLITE_CORRUPT_BKPT; + }else{ + rc = walCheckpoint(pWal, db, eMode2, xBusy2, pBusyArg, sync_flags, zBuf); + } + + /* If no error occurred, set the output variables. */ + if( rc==SQLITE_OK || rc==SQLITE_BUSY ){ + if( pnLog ) *pnLog = (int)pWal->hdr.mxFrame; + if( pnCkpt ) *pnCkpt = (int)(walCkptInfo(pWal)->nBackfill); + } + } + + if( isChanged ){ + /* If a new wal-index header was loaded before the checkpoint was + ** performed, then the pager-cache associated with pWal is now + ** out of date. So zero the cached wal-index header to ensure that + ** next time the pager opens a snapshot on this database it knows that + ** the cache needs to be reset. + */ + memset(&pWal->hdr, 0, sizeof(WalIndexHdr)); + } + + walDisableBlocking(pWal); + sqlite3WalDb(pWal, 0); + + /* Release the locks. */ + sqlite3WalEndWriteTransaction(pWal); + if( pWal->ckptLock ){ + walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1); + pWal->ckptLock = 0; + } + WALTRACE(("WAL%p: checkpoint %s\n", pWal, rc ? "failed" : "ok")); +#ifdef SQLITE_ENABLE_SETLK_TIMEOUT + if( rc==SQLITE_BUSY_TIMEOUT ) rc = SQLITE_BUSY; +#endif + return (rc==SQLITE_OK && eMode!=eMode2 ? SQLITE_BUSY : rc); +} + +/* Return the value to pass to a sqlite3_wal_hook callback, the +** number of frames in the WAL at the point of the last commit since +** sqlite3WalCallback() was called. If no commits have occurred since +** the last call, then return 0. +*/ +int sqlite3WalCallback(Wal *pWal){ + u32 ret = 0; + if( pWal ){ + ret = pWal->iCallback; + pWal->iCallback = 0; + } + return (int)ret; +} + +/* +** This function is called to change the WAL subsystem into or out +** of locking_mode=EXCLUSIVE. +** +** If op is zero, then attempt to change from locking_mode=EXCLUSIVE +** into locking_mode=NORMAL. This means that we must acquire a lock +** on the pWal->readLock byte. If the WAL is already in locking_mode=NORMAL +** or if the acquisition of the lock fails, then return 0. If the +** transition out of exclusive-mode is successful, return 1. This +** operation must occur while the pager is still holding the exclusive +** lock on the main database file. +** +** If op is one, then change from locking_mode=NORMAL into +** locking_mode=EXCLUSIVE. This means that the pWal->readLock must +** be released. Return 1 if the transition is made and 0 if the +** WAL is already in exclusive-locking mode - meaning that this +** routine is a no-op. The pager must already hold the exclusive lock +** on the main database file before invoking this operation. +** +** If op is negative, then do a dry-run of the op==1 case but do +** not actually change anything. The pager uses this to see if it +** should acquire the database exclusive lock prior to invoking +** the op==1 case. +*/ +int sqlite3WalExclusiveMode(Wal *pWal, int op){ + int rc; + assert( pWal->writeLock==0 ); + assert( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE || op==-1 ); + + /* pWal->readLock is usually set, but might be -1 if there was a + ** prior error while attempting to acquire are read-lock. This cannot + ** happen if the connection is actually in exclusive mode (as no xShmLock + ** locks are taken in this case). Nor should the pager attempt to + ** upgrade to exclusive-mode following such an error. + */ + assert( pWal->readLock>=0 || pWal->lockError ); + assert( pWal->readLock>=0 || (op<=0 && pWal->exclusiveMode==0) ); + + if( op==0 ){ + if( pWal->exclusiveMode!=WAL_NORMAL_MODE ){ + pWal->exclusiveMode = WAL_NORMAL_MODE; + if( walLockShared(pWal, WAL_READ_LOCK(pWal->readLock))!=SQLITE_OK ){ + pWal->exclusiveMode = WAL_EXCLUSIVE_MODE; + } + rc = pWal->exclusiveMode==WAL_NORMAL_MODE; + }else{ + /* Already in locking_mode=NORMAL */ + rc = 0; + } + }else if( op>0 ){ + assert( pWal->exclusiveMode==WAL_NORMAL_MODE ); + assert( pWal->readLock>=0 ); + walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock)); + pWal->exclusiveMode = WAL_EXCLUSIVE_MODE; + rc = 1; + }else{ + rc = pWal->exclusiveMode==WAL_NORMAL_MODE; + } + return rc; +} + +/* +** Return true if the argument is non-NULL and the WAL module is using +** heap-memory for the wal-index. Otherwise, if the argument is NULL or the +** WAL module is using shared-memory, return false. +*/ +int sqlite3WalHeapMemory(Wal *pWal){ + return (pWal && pWal->exclusiveMode==WAL_HEAPMEMORY_MODE ); +} + +#ifdef SQLITE_ENABLE_SNAPSHOT +/* Create a snapshot object. The content of a snapshot is opaque to +** every other subsystem, so the WAL module can put whatever it needs +** in the object. +*/ +int sqlite3WalSnapshotGet(Wal *pWal, sqlite3_snapshot **ppSnapshot){ + int rc = SQLITE_OK; + WalIndexHdr *pRet; + static const u32 aZero[4] = { 0, 0, 0, 0 }; + + assert( pWal->readLock>=0 && pWal->writeLock==0 ); + + if( memcmp(&pWal->hdr.aFrameCksum[0],aZero,16)==0 ){ + *ppSnapshot = 0; + return SQLITE_ERROR; + } + pRet = (WalIndexHdr*)sqlite3_malloc(sizeof(WalIndexHdr)); + if( pRet==0 ){ + rc = SQLITE_NOMEM_BKPT; + }else{ + memcpy(pRet, &pWal->hdr, sizeof(WalIndexHdr)); + *ppSnapshot = (sqlite3_snapshot*)pRet; + } + + return rc; +} + +/* Try to open on pSnapshot when the next read-transaction starts +*/ +void sqlite3WalSnapshotOpen( + Wal *pWal, + sqlite3_snapshot *pSnapshot +){ + pWal->pSnapshot = (WalIndexHdr*)pSnapshot; +} + +/* +** Return a +ve value if snapshot p1 is newer than p2. A -ve value if +** p1 is older than p2 and zero if p1 and p2 are the same snapshot. +*/ +int sqlite3_snapshot_cmp(sqlite3_snapshot *p1, sqlite3_snapshot *p2){ + WalIndexHdr *pHdr1 = (WalIndexHdr*)p1; + WalIndexHdr *pHdr2 = (WalIndexHdr*)p2; + + /* aSalt[0] is a copy of the value stored in the wal file header. It + ** is incremented each time the wal file is restarted. */ + if( pHdr1->aSalt[0]<pHdr2->aSalt[0] ) return -1; + if( pHdr1->aSalt[0]>pHdr2->aSalt[0] ) return +1; + if( pHdr1->mxFrame<pHdr2->mxFrame ) return -1; + if( pHdr1->mxFrame>pHdr2->mxFrame ) return +1; + return 0; +} + +/* +** The caller currently has a read transaction open on the database. +** This function takes a SHARED lock on the CHECKPOINTER slot and then +** checks if the snapshot passed as the second argument is still +** available. If so, SQLITE_OK is returned. +** +** If the snapshot is not available, SQLITE_ERROR is returned. Or, if +** the CHECKPOINTER lock cannot be obtained, SQLITE_BUSY. If any error +** occurs (any value other than SQLITE_OK is returned), the CHECKPOINTER +** lock is released before returning. +*/ +int sqlite3WalSnapshotCheck(Wal *pWal, sqlite3_snapshot *pSnapshot){ + int rc; + rc = walLockShared(pWal, WAL_CKPT_LOCK); + if( rc==SQLITE_OK ){ + WalIndexHdr *pNew = (WalIndexHdr*)pSnapshot; + if( memcmp(pNew->aSalt, pWal->hdr.aSalt, sizeof(pWal->hdr.aSalt)) + || pNew->mxFrame<walCkptInfo(pWal)->nBackfillAttempted + ){ + rc = SQLITE_ERROR_SNAPSHOT; + walUnlockShared(pWal, WAL_CKPT_LOCK); + } + } + return rc; +} + +/* +** Release a lock obtained by an earlier successful call to +** sqlite3WalSnapshotCheck(). +*/ +void sqlite3WalSnapshotUnlock(Wal *pWal){ + assert( pWal ); + walUnlockShared(pWal, WAL_CKPT_LOCK); +} + + +#endif /* SQLITE_ENABLE_SNAPSHOT */ + +#ifdef SQLITE_ENABLE_ZIPVFS +/* +** If the argument is not NULL, it points to a Wal object that holds a +** read-lock. This function returns the database page-size if it is known, +** or zero if it is not (or if pWal is NULL). +*/ +int sqlite3WalFramesize(Wal *pWal){ + assert( pWal==0 || pWal->readLock>=0 ); + return (pWal ? pWal->szPage : 0); +} +#endif + +/* Return the sqlite3_file object for the WAL file +*/ +sqlite3_file *sqlite3WalFile(Wal *pWal){ + return pWal->pWalFd; +} + +#endif /* #ifndef SQLITE_OMIT_WAL */ |