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Diffstat (limited to 'src/include/storage/bufpage.h')
| -rw-r--r-- | src/include/storage/bufpage.h | 457 |
1 files changed, 457 insertions, 0 deletions
diff --git a/src/include/storage/bufpage.h b/src/include/storage/bufpage.h new file mode 100644 index 0000000..c86ccda --- /dev/null +++ b/src/include/storage/bufpage.h @@ -0,0 +1,457 @@ +/*------------------------------------------------------------------------- + * + * bufpage.h + * Standard POSTGRES buffer page definitions. + * + * + * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * src/include/storage/bufpage.h + * + *------------------------------------------------------------------------- + */ +#ifndef BUFPAGE_H +#define BUFPAGE_H + +#include "access/xlogdefs.h" +#include "storage/block.h" +#include "storage/item.h" +#include "storage/off.h" + +/* + * A postgres disk page is an abstraction layered on top of a postgres + * disk block (which is simply a unit of i/o, see block.h). + * + * specifically, while a disk block can be unformatted, a postgres + * disk page is always a slotted page of the form: + * + * +----------------+---------------------------------+ + * | PageHeaderData | linp1 linp2 linp3 ... | + * +-----------+----+---------------------------------+ + * | ... linpN | | + * +-----------+--------------------------------------+ + * | ^ pd_lower | + * | | + * | v pd_upper | + * +-------------+------------------------------------+ + * | | tupleN ... | + * +-------------+------------------+-----------------+ + * | ... tuple3 tuple2 tuple1 | "special space" | + * +--------------------------------+-----------------+ + * ^ pd_special + * + * a page is full when nothing can be added between pd_lower and + * pd_upper. + * + * all blocks written out by an access method must be disk pages. + * + * EXCEPTIONS: + * + * obviously, a page is not formatted before it is initialized by + * a call to PageInit. + * + * NOTES: + * + * linp1..N form an ItemId (line pointer) array. ItemPointers point + * to a physical block number and a logical offset (line pointer + * number) within that block/page. Note that OffsetNumbers + * conventionally start at 1, not 0. + * + * tuple1..N are added "backwards" on the page. Since an ItemPointer + * offset is used to access an ItemId entry rather than an actual + * byte-offset position, tuples can be physically shuffled on a page + * whenever the need arises. This indirection also keeps crash recovery + * relatively simple, because the low-level details of page space + * management can be controlled by standard buffer page code during + * logging, and during recovery. + * + * AM-generic per-page information is kept in PageHeaderData. + * + * AM-specific per-page data (if any) is kept in the area marked "special + * space"; each AM has an "opaque" structure defined somewhere that is + * stored as the page trailer. an access method should always + * initialize its pages with PageInit and then set its own opaque + * fields. + */ + +typedef Pointer Page; + + +/* + * location (byte offset) within a page. + * + * note that this is actually limited to 2^15 because we have limited + * ItemIdData.lp_off and ItemIdData.lp_len to 15 bits (see itemid.h). + */ +typedef uint16 LocationIndex; + + +/* + * For historical reasons, the 64-bit LSN value is stored as two 32-bit + * values. + */ +typedef struct +{ + uint32 xlogid; /* high bits */ + uint32 xrecoff; /* low bits */ +} PageXLogRecPtr; + +#define PageXLogRecPtrGet(val) \ + ((uint64) (val).xlogid << 32 | (val).xrecoff) +#define PageXLogRecPtrSet(ptr, lsn) \ + ((ptr).xlogid = (uint32) ((lsn) >> 32), (ptr).xrecoff = (uint32) (lsn)) + +/* + * disk page organization + * + * space management information generic to any page + * + * pd_lsn - identifies xlog record for last change to this page. + * pd_checksum - page checksum, if set. + * pd_flags - flag bits. + * pd_lower - offset to start of free space. + * pd_upper - offset to end of free space. + * pd_special - offset to start of special space. + * pd_pagesize_version - size in bytes and page layout version number. + * pd_prune_xid - oldest XID among potentially prunable tuples on page. + * + * The LSN is used by the buffer manager to enforce the basic rule of WAL: + * "thou shalt write xlog before data". A dirty buffer cannot be dumped + * to disk until xlog has been flushed at least as far as the page's LSN. + * + * pd_checksum stores the page checksum, if it has been set for this page; + * zero is a valid value for a checksum. If a checksum is not in use then + * we leave the field unset. This will typically mean the field is zero + * though non-zero values may also be present if databases have been + * pg_upgraded from releases prior to 9.3, when the same byte offset was + * used to store the current timelineid when the page was last updated. + * Note that there is no indication on a page as to whether the checksum + * is valid or not, a deliberate design choice which avoids the problem + * of relying on the page contents to decide whether to verify it. Hence + * there are no flag bits relating to checksums. + * + * pd_prune_xid is a hint field that helps determine whether pruning will be + * useful. It is currently unused in index pages. + * + * The page version number and page size are packed together into a single + * uint16 field. This is for historical reasons: before PostgreSQL 7.3, + * there was no concept of a page version number, and doing it this way + * lets us pretend that pre-7.3 databases have page version number zero. + * We constrain page sizes to be multiples of 256, leaving the low eight + * bits available for a version number. + * + * Minimum possible page size is perhaps 64B to fit page header, opaque space + * and a minimal tuple; of course, in reality you want it much bigger, so + * the constraint on pagesize mod 256 is not an important restriction. + * On the high end, we can only support pages up to 32KB because lp_off/lp_len + * are 15 bits. + */ + +typedef struct PageHeaderData +{ + /* XXX LSN is member of *any* block, not only page-organized ones */ + PageXLogRecPtr pd_lsn; /* LSN: next byte after last byte of xlog + * record for last change to this page */ + uint16 pd_checksum; /* checksum */ + uint16 pd_flags; /* flag bits, see below */ + LocationIndex pd_lower; /* offset to start of free space */ + LocationIndex pd_upper; /* offset to end of free space */ + LocationIndex pd_special; /* offset to start of special space */ + uint16 pd_pagesize_version; + TransactionId pd_prune_xid; /* oldest prunable XID, or zero if none */ + ItemIdData pd_linp[FLEXIBLE_ARRAY_MEMBER]; /* line pointer array */ +} PageHeaderData; + +typedef PageHeaderData *PageHeader; + +/* + * pd_flags contains the following flag bits. Undefined bits are initialized + * to zero and may be used in the future. + * + * PD_HAS_FREE_LINES is set if there are any LP_UNUSED line pointers before + * pd_lower. This should be considered a hint rather than the truth, since + * changes to it are not WAL-logged. + * + * PD_PAGE_FULL is set if an UPDATE doesn't find enough free space in the + * page for its new tuple version; this suggests that a prune is needed. + * Again, this is just a hint. + */ +#define PD_HAS_FREE_LINES 0x0001 /* are there any unused line pointers? */ +#define PD_PAGE_FULL 0x0002 /* not enough free space for new tuple? */ +#define PD_ALL_VISIBLE 0x0004 /* all tuples on page are visible to + * everyone */ + +#define PD_VALID_FLAG_BITS 0x0007 /* OR of all valid pd_flags bits */ + +/* + * Page layout version number 0 is for pre-7.3 Postgres releases. + * Releases 7.3 and 7.4 use 1, denoting a new HeapTupleHeader layout. + * Release 8.0 uses 2; it changed the HeapTupleHeader layout again. + * Release 8.1 uses 3; it redefined HeapTupleHeader infomask bits. + * Release 8.3 uses 4; it changed the HeapTupleHeader layout again, and + * added the pd_flags field (by stealing some bits from pd_tli), + * as well as adding the pd_prune_xid field (which enlarges the header). + * + * As of Release 9.3, the checksum version must also be considered when + * handling pages. + */ +#define PG_PAGE_LAYOUT_VERSION 4 +#define PG_DATA_CHECKSUM_VERSION 1 + +/* ---------------------------------------------------------------- + * page support macros + * ---------------------------------------------------------------- + */ + +/* + * PageIsValid + * True iff page is valid. + */ +#define PageIsValid(page) PointerIsValid(page) + +/* + * line pointer(s) do not count as part of header + */ +#define SizeOfPageHeaderData (offsetof(PageHeaderData, pd_linp)) + +/* + * PageIsEmpty + * returns true iff no itemid has been allocated on the page + */ +#define PageIsEmpty(page) \ + (((PageHeader) (page))->pd_lower <= SizeOfPageHeaderData) + +/* + * PageIsNew + * returns true iff page has not been initialized (by PageInit) + */ +#define PageIsNew(page) (((PageHeader) (page))->pd_upper == 0) + +/* + * PageGetItemId + * Returns an item identifier of a page. + */ +#define PageGetItemId(page, offsetNumber) \ + ((ItemId) (&((PageHeader) (page))->pd_linp[(offsetNumber) - 1])) + +/* + * PageGetContents + * To be used in cases where the page does not contain line pointers. + * + * Note: prior to 8.3 this was not guaranteed to yield a MAXALIGN'd result. + * Now it is. Beware of old code that might think the offset to the contents + * is just SizeOfPageHeaderData rather than MAXALIGN(SizeOfPageHeaderData). + */ +#define PageGetContents(page) \ + ((char *) (page) + MAXALIGN(SizeOfPageHeaderData)) + +/* ---------------- + * macros to access page size info + * ---------------- + */ + +/* + * PageSizeIsValid + * True iff the page size is valid. + */ +#define PageSizeIsValid(pageSize) ((pageSize) == BLCKSZ) + +/* + * PageGetPageSize + * Returns the page size of a page. + * + * this can only be called on a formatted page (unlike + * BufferGetPageSize, which can be called on an unformatted page). + * however, it can be called on a page that is not stored in a buffer. + */ +#define PageGetPageSize(page) \ + ((Size) (((PageHeader) (page))->pd_pagesize_version & (uint16) 0xFF00)) + +/* + * PageGetPageLayoutVersion + * Returns the page layout version of a page. + */ +#define PageGetPageLayoutVersion(page) \ + (((PageHeader) (page))->pd_pagesize_version & 0x00FF) + +/* + * PageSetPageSizeAndVersion + * Sets the page size and page layout version number of a page. + * + * We could support setting these two values separately, but there's + * no real need for it at the moment. + */ +#define PageSetPageSizeAndVersion(page, size, version) \ +( \ + AssertMacro(((size) & 0xFF00) == (size)), \ + AssertMacro(((version) & 0x00FF) == (version)), \ + ((PageHeader) (page))->pd_pagesize_version = (size) | (version) \ +) + +/* ---------------- + * page special data macros + * ---------------- + */ +/* + * PageGetSpecialSize + * Returns size of special space on a page. + */ +#define PageGetSpecialSize(page) \ + ((uint16) (PageGetPageSize(page) - ((PageHeader)(page))->pd_special)) + +/* + * Using assertions, validate that the page special pointer is OK. + * + * This is intended to catch use of the pointer before page initialization. + * It is implemented as a function due to the limitations of the MSVC + * compiler, which choked on doing all these tests within another macro. We + * return true so that AssertMacro() can be used while still getting the + * specifics from the macro failure within this function. + */ +static inline bool +PageValidateSpecialPointer(Page page) +{ + Assert(PageIsValid(page)); + Assert(((PageHeader) (page))->pd_special <= BLCKSZ); + Assert(((PageHeader) (page))->pd_special >= SizeOfPageHeaderData); + + return true; +} + +/* + * PageGetSpecialPointer + * Returns pointer to special space on a page. + */ +#define PageGetSpecialPointer(page) \ +( \ + AssertMacro(PageValidateSpecialPointer(page)), \ + (char *) ((char *) (page) + ((PageHeader) (page))->pd_special) \ +) + +/* + * PageGetItem + * Retrieves an item on the given page. + * + * Note: + * This does not change the status of any of the resources passed. + * The semantics may change in the future. + */ +#define PageGetItem(page, itemId) \ +( \ + AssertMacro(PageIsValid(page)), \ + AssertMacro(ItemIdHasStorage(itemId)), \ + (Item)(((char *)(page)) + ItemIdGetOffset(itemId)) \ +) + +/* + * PageGetMaxOffsetNumber + * Returns the maximum offset number used by the given page. + * Since offset numbers are 1-based, this is also the number + * of items on the page. + * + * NOTE: if the page is not initialized (pd_lower == 0), we must + * return zero to ensure sane behavior. Accept double evaluation + * of the argument so that we can ensure this. + */ +#define PageGetMaxOffsetNumber(page) \ + (((PageHeader) (page))->pd_lower <= SizeOfPageHeaderData ? 0 : \ + ((((PageHeader) (page))->pd_lower - SizeOfPageHeaderData) \ + / sizeof(ItemIdData))) + +/* + * Additional macros for access to page headers. (Beware multiple evaluation + * of the arguments!) + */ +#define PageGetLSN(page) \ + PageXLogRecPtrGet(((PageHeader) (page))->pd_lsn) +#define PageSetLSN(page, lsn) \ + PageXLogRecPtrSet(((PageHeader) (page))->pd_lsn, lsn) + +#define PageHasFreeLinePointers(page) \ + (((PageHeader) (page))->pd_flags & PD_HAS_FREE_LINES) +#define PageSetHasFreeLinePointers(page) \ + (((PageHeader) (page))->pd_flags |= PD_HAS_FREE_LINES) +#define PageClearHasFreeLinePointers(page) \ + (((PageHeader) (page))->pd_flags &= ~PD_HAS_FREE_LINES) + +#define PageIsFull(page) \ + (((PageHeader) (page))->pd_flags & PD_PAGE_FULL) +#define PageSetFull(page) \ + (((PageHeader) (page))->pd_flags |= PD_PAGE_FULL) +#define PageClearFull(page) \ + (((PageHeader) (page))->pd_flags &= ~PD_PAGE_FULL) + +#define PageIsAllVisible(page) \ + (((PageHeader) (page))->pd_flags & PD_ALL_VISIBLE) +#define PageSetAllVisible(page) \ + (((PageHeader) (page))->pd_flags |= PD_ALL_VISIBLE) +#define PageClearAllVisible(page) \ + (((PageHeader) (page))->pd_flags &= ~PD_ALL_VISIBLE) + +#define PageSetPrunable(page, xid) \ +do { \ + Assert(TransactionIdIsNormal(xid)); \ + if (!TransactionIdIsValid(((PageHeader) (page))->pd_prune_xid) || \ + TransactionIdPrecedes(xid, ((PageHeader) (page))->pd_prune_xid)) \ + ((PageHeader) (page))->pd_prune_xid = (xid); \ +} while (0) +#define PageClearPrunable(page) \ + (((PageHeader) (page))->pd_prune_xid = InvalidTransactionId) + + +/* ---------------------------------------------------------------- + * extern declarations + * ---------------------------------------------------------------- + */ + +/* flags for PageAddItemExtended() */ +#define PAI_OVERWRITE (1 << 0) +#define PAI_IS_HEAP (1 << 1) + +/* flags for PageIsVerifiedExtended() */ +#define PIV_LOG_WARNING (1 << 0) +#define PIV_REPORT_STAT (1 << 1) + +#define PageAddItem(page, item, size, offsetNumber, overwrite, is_heap) \ + PageAddItemExtended(page, item, size, offsetNumber, \ + ((overwrite) ? PAI_OVERWRITE : 0) | \ + ((is_heap) ? PAI_IS_HEAP : 0)) + +#define PageIsVerified(page, blkno) \ + PageIsVerifiedExtended(page, blkno, \ + PIV_LOG_WARNING | PIV_REPORT_STAT) + +/* + * Check that BLCKSZ is a multiple of sizeof(size_t). In + * PageIsVerifiedExtended(), it is much faster to check if a page is + * full of zeroes using the native word size. Note that this assertion + * is kept within a header to make sure that StaticAssertDecl() works + * across various combinations of platforms and compilers. + */ +StaticAssertDecl(BLCKSZ == ((BLCKSZ / sizeof(size_t)) * sizeof(size_t)), + "BLCKSZ has to be a multiple of sizeof(size_t)"); + +extern void PageInit(Page page, Size pageSize, Size specialSize); +extern bool PageIsVerifiedExtended(Page page, BlockNumber blkno, int flags); +extern OffsetNumber PageAddItemExtended(Page page, Item item, Size size, + OffsetNumber offsetNumber, int flags); +extern Page PageGetTempPage(Page page); +extern Page PageGetTempPageCopy(Page page); +extern Page PageGetTempPageCopySpecial(Page page); +extern void PageRestoreTempPage(Page tempPage, Page oldPage); +extern void PageRepairFragmentation(Page page); +extern void PageTruncateLinePointerArray(Page page); +extern Size PageGetFreeSpace(Page page); +extern Size PageGetFreeSpaceForMultipleTuples(Page page, int ntups); +extern Size PageGetExactFreeSpace(Page page); +extern Size PageGetHeapFreeSpace(Page page); +extern void PageIndexTupleDelete(Page page, OffsetNumber offset); +extern void PageIndexMultiDelete(Page page, OffsetNumber *itemnos, int nitems); +extern void PageIndexTupleDeleteNoCompact(Page page, OffsetNumber offset); +extern bool PageIndexTupleOverwrite(Page page, OffsetNumber offnum, + Item newtup, Size newsize); +extern char *PageSetChecksumCopy(Page page, BlockNumber blkno); +extern void PageSetChecksumInplace(Page page, BlockNumber blkno); + +#endif /* BUFPAGE_H */ |