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Diffstat (limited to 'src/backend/access/transam/xlogutils.c')
| -rw-r--r-- | src/backend/access/transam/xlogutils.c | 1064 |
1 files changed, 1064 insertions, 0 deletions
diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c new file mode 100644 index 0000000..702c8c1 --- /dev/null +++ b/src/backend/access/transam/xlogutils.c @@ -0,0 +1,1064 @@ +/*------------------------------------------------------------------------- + * + * xlogutils.c + * + * PostgreSQL write-ahead log manager utility routines + * + * This file contains support routines that are used by XLOG replay functions. + * None of this code is used during normal system operation. + * + * + * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * src/backend/access/transam/xlogutils.c + * + *------------------------------------------------------------------------- + */ +#include "postgres.h" + +#include <unistd.h> + +#include "access/timeline.h" +#include "access/xlogrecovery.h" +#include "access/xlog_internal.h" +#include "access/xlogprefetcher.h" +#include "access/xlogutils.h" +#include "miscadmin.h" +#include "pgstat.h" +#include "storage/fd.h" +#include "storage/smgr.h" +#include "utils/guc.h" +#include "utils/hsearch.h" +#include "utils/rel.h" + + +/* GUC variable */ +bool ignore_invalid_pages = false; + +/* + * Are we doing recovery from XLOG? + * + * This is only ever true in the startup process; it should be read as meaning + * "this process is replaying WAL records", rather than "the system is in + * recovery mode". It should be examined primarily by functions that need + * to act differently when called from a WAL redo function (e.g., to skip WAL + * logging). To check whether the system is in recovery regardless of which + * process you're running in, use RecoveryInProgress() but only after shared + * memory startup and lock initialization. + * + * This is updated from xlog.c and xlogrecovery.c, but lives here because + * it's mostly read by WAL redo functions. + */ +bool InRecovery = false; + +/* Are we in Hot Standby mode? Only valid in startup process, see xlogutils.h */ +HotStandbyState standbyState = STANDBY_DISABLED; + +/* + * During XLOG replay, we may see XLOG records for incremental updates of + * pages that no longer exist, because their relation was later dropped or + * truncated. (Note: this is only possible when full_page_writes = OFF, + * since when it's ON, the first reference we see to a page should always + * be a full-page rewrite not an incremental update.) Rather than simply + * ignoring such records, we make a note of the referenced page, and then + * complain if we don't actually see a drop or truncate covering the page + * later in replay. + */ +typedef struct xl_invalid_page_key +{ + RelFileNode node; /* the relation */ + ForkNumber forkno; /* the fork number */ + BlockNumber blkno; /* the page */ +} xl_invalid_page_key; + +typedef struct xl_invalid_page +{ + xl_invalid_page_key key; /* hash key ... must be first */ + bool present; /* page existed but contained zeroes */ +} xl_invalid_page; + +static HTAB *invalid_page_tab = NULL; + +static int read_local_xlog_page_guts(XLogReaderState *state, XLogRecPtr targetPagePtr, + int reqLen, XLogRecPtr targetRecPtr, + char *cur_page, bool wait_for_wal); + +/* Report a reference to an invalid page */ +static void +report_invalid_page(int elevel, RelFileNode node, ForkNumber forkno, + BlockNumber blkno, bool present) +{ + char *path = relpathperm(node, forkno); + + if (present) + elog(elevel, "page %u of relation %s is uninitialized", + blkno, path); + else + elog(elevel, "page %u of relation %s does not exist", + blkno, path); + pfree(path); +} + +/* Log a reference to an invalid page */ +static void +log_invalid_page(RelFileNode node, ForkNumber forkno, BlockNumber blkno, + bool present) +{ + xl_invalid_page_key key; + xl_invalid_page *hentry; + bool found; + + /* + * Once recovery has reached a consistent state, the invalid-page table + * should be empty and remain so. If a reference to an invalid page is + * found after consistency is reached, PANIC immediately. This might seem + * aggressive, but it's better than letting the invalid reference linger + * in the hash table until the end of recovery and PANIC there, which + * might come only much later if this is a standby server. + */ + if (reachedConsistency) + { + report_invalid_page(WARNING, node, forkno, blkno, present); + elog(ignore_invalid_pages ? WARNING : PANIC, + "WAL contains references to invalid pages"); + } + + /* + * Log references to invalid pages at DEBUG1 level. This allows some + * tracing of the cause (note the elog context mechanism will tell us + * something about the XLOG record that generated the reference). + */ + if (message_level_is_interesting(DEBUG1)) + report_invalid_page(DEBUG1, node, forkno, blkno, present); + + if (invalid_page_tab == NULL) + { + /* create hash table when first needed */ + HASHCTL ctl; + + ctl.keysize = sizeof(xl_invalid_page_key); + ctl.entrysize = sizeof(xl_invalid_page); + + invalid_page_tab = hash_create("XLOG invalid-page table", + 100, + &ctl, + HASH_ELEM | HASH_BLOBS); + } + + /* we currently assume xl_invalid_page_key contains no padding */ + key.node = node; + key.forkno = forkno; + key.blkno = blkno; + hentry = (xl_invalid_page *) + hash_search(invalid_page_tab, (void *) &key, HASH_ENTER, &found); + + if (!found) + { + /* hash_search already filled in the key */ + hentry->present = present; + } + else + { + /* repeat reference ... leave "present" as it was */ + } +} + +/* Forget any invalid pages >= minblkno, because they've been dropped */ +static void +forget_invalid_pages(RelFileNode node, ForkNumber forkno, BlockNumber minblkno) +{ + HASH_SEQ_STATUS status; + xl_invalid_page *hentry; + + if (invalid_page_tab == NULL) + return; /* nothing to do */ + + hash_seq_init(&status, invalid_page_tab); + + while ((hentry = (xl_invalid_page *) hash_seq_search(&status)) != NULL) + { + if (RelFileNodeEquals(hentry->key.node, node) && + hentry->key.forkno == forkno && + hentry->key.blkno >= minblkno) + { + if (message_level_is_interesting(DEBUG2)) + { + char *path = relpathperm(hentry->key.node, forkno); + + elog(DEBUG2, "page %u of relation %s has been dropped", + hentry->key.blkno, path); + pfree(path); + } + + if (hash_search(invalid_page_tab, + (void *) &hentry->key, + HASH_REMOVE, NULL) == NULL) + elog(ERROR, "hash table corrupted"); + } + } +} + +/* Forget any invalid pages in a whole database */ +static void +forget_invalid_pages_db(Oid dbid) +{ + HASH_SEQ_STATUS status; + xl_invalid_page *hentry; + + if (invalid_page_tab == NULL) + return; /* nothing to do */ + + hash_seq_init(&status, invalid_page_tab); + + while ((hentry = (xl_invalid_page *) hash_seq_search(&status)) != NULL) + { + if (hentry->key.node.dbNode == dbid) + { + if (message_level_is_interesting(DEBUG2)) + { + char *path = relpathperm(hentry->key.node, hentry->key.forkno); + + elog(DEBUG2, "page %u of relation %s has been dropped", + hentry->key.blkno, path); + pfree(path); + } + + if (hash_search(invalid_page_tab, + (void *) &hentry->key, + HASH_REMOVE, NULL) == NULL) + elog(ERROR, "hash table corrupted"); + } + } +} + +/* Are there any unresolved references to invalid pages? */ +bool +XLogHaveInvalidPages(void) +{ + if (invalid_page_tab != NULL && + hash_get_num_entries(invalid_page_tab) > 0) + return true; + return false; +} + +/* Complain about any remaining invalid-page entries */ +void +XLogCheckInvalidPages(void) +{ + HASH_SEQ_STATUS status; + xl_invalid_page *hentry; + bool foundone = false; + + if (invalid_page_tab == NULL) + return; /* nothing to do */ + + hash_seq_init(&status, invalid_page_tab); + + /* + * Our strategy is to emit WARNING messages for all remaining entries and + * only PANIC after we've dumped all the available info. + */ + while ((hentry = (xl_invalid_page *) hash_seq_search(&status)) != NULL) + { + report_invalid_page(WARNING, hentry->key.node, hentry->key.forkno, + hentry->key.blkno, hentry->present); + foundone = true; + } + + if (foundone) + elog(ignore_invalid_pages ? WARNING : PANIC, + "WAL contains references to invalid pages"); + + hash_destroy(invalid_page_tab); + invalid_page_tab = NULL; +} + + +/* + * XLogReadBufferForRedo + * Read a page during XLOG replay + * + * Reads a block referenced by a WAL record into shared buffer cache, and + * determines what needs to be done to redo the changes to it. If the WAL + * record includes a full-page image of the page, it is restored. + * + * 'record.EndRecPtr' is compared to the page's LSN to determine if the record + * has already been replayed. 'block_id' is the ID number the block was + * registered with, when the WAL record was created. + * + * Returns one of the following: + * + * BLK_NEEDS_REDO - changes from the WAL record need to be applied + * BLK_DONE - block doesn't need replaying + * BLK_RESTORED - block was restored from a full-page image included in + * the record + * BLK_NOTFOUND - block was not found (because it was truncated away by + * an operation later in the WAL stream) + * + * On return, the buffer is locked in exclusive-mode, and returned in *buf. + * Note that the buffer is locked and returned even if it doesn't need + * replaying. (Getting the buffer lock is not really necessary during + * single-process crash recovery, but some subroutines such as MarkBufferDirty + * will complain if we don't have the lock. In hot standby mode it's + * definitely necessary.) + * + * Note: when a backup block is available in XLOG with the BKPIMAGE_APPLY flag + * set, we restore it, even if the page in the database appears newer. This + * is to protect ourselves against database pages that were partially or + * incorrectly written during a crash. We assume that the XLOG data must be + * good because it has passed a CRC check, while the database page might not + * be. This will force us to replay all subsequent modifications of the page + * that appear in XLOG, rather than possibly ignoring them as already + * applied, but that's not a huge drawback. + */ +XLogRedoAction +XLogReadBufferForRedo(XLogReaderState *record, uint8 block_id, + Buffer *buf) +{ + return XLogReadBufferForRedoExtended(record, block_id, RBM_NORMAL, + false, buf); +} + +/* + * Pin and lock a buffer referenced by a WAL record, for the purpose of + * re-initializing it. + */ +Buffer +XLogInitBufferForRedo(XLogReaderState *record, uint8 block_id) +{ + Buffer buf; + + XLogReadBufferForRedoExtended(record, block_id, RBM_ZERO_AND_LOCK, false, + &buf); + return buf; +} + +/* + * XLogReadBufferForRedoExtended + * Like XLogReadBufferForRedo, but with extra options. + * + * In RBM_ZERO_* modes, if the page doesn't exist, the relation is extended + * with all-zeroes pages up to the referenced block number. In + * RBM_ZERO_AND_LOCK and RBM_ZERO_AND_CLEANUP_LOCK modes, the return value + * is always BLK_NEEDS_REDO. + * + * (The RBM_ZERO_AND_CLEANUP_LOCK mode is redundant with the get_cleanup_lock + * parameter. Do not use an inconsistent combination!) + * + * If 'get_cleanup_lock' is true, a "cleanup lock" is acquired on the buffer + * using LockBufferForCleanup(), instead of a regular exclusive lock. + */ +XLogRedoAction +XLogReadBufferForRedoExtended(XLogReaderState *record, + uint8 block_id, + ReadBufferMode mode, bool get_cleanup_lock, + Buffer *buf) +{ + XLogRecPtr lsn = record->EndRecPtr; + RelFileNode rnode; + ForkNumber forknum; + BlockNumber blkno; + Buffer prefetch_buffer; + Page page; + bool zeromode; + bool willinit; + + if (!XLogRecGetBlockTagExtended(record, block_id, &rnode, &forknum, &blkno, + &prefetch_buffer)) + { + /* Caller specified a bogus block_id */ + elog(PANIC, "failed to locate backup block with ID %d in WAL record", + block_id); + } + + /* + * Make sure that if the block is marked with WILL_INIT, the caller is + * going to initialize it. And vice versa. + */ + zeromode = (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK); + willinit = (XLogRecGetBlock(record, block_id)->flags & BKPBLOCK_WILL_INIT) != 0; + if (willinit && !zeromode) + elog(PANIC, "block with WILL_INIT flag in WAL record must be zeroed by redo routine"); + if (!willinit && zeromode) + elog(PANIC, "block to be initialized in redo routine must be marked with WILL_INIT flag in the WAL record"); + + /* If it has a full-page image and it should be restored, do it. */ + if (XLogRecBlockImageApply(record, block_id)) + { + Assert(XLogRecHasBlockImage(record, block_id)); + *buf = XLogReadBufferExtended(rnode, forknum, blkno, + get_cleanup_lock ? RBM_ZERO_AND_CLEANUP_LOCK : RBM_ZERO_AND_LOCK, + prefetch_buffer); + page = BufferGetPage(*buf); + if (!RestoreBlockImage(record, block_id, page)) + ereport(ERROR, + (errcode(ERRCODE_INTERNAL_ERROR), + errmsg_internal("%s", record->errormsg_buf))); + + /* + * The page may be uninitialized. If so, we can't set the LSN because + * that would corrupt the page. + */ + if (!PageIsNew(page)) + { + PageSetLSN(page, lsn); + } + + MarkBufferDirty(*buf); + + /* + * At the end of crash recovery the init forks of unlogged relations + * are copied, without going through shared buffers. So we need to + * force the on-disk state of init forks to always be in sync with the + * state in shared buffers. + */ + if (forknum == INIT_FORKNUM) + FlushOneBuffer(*buf); + + return BLK_RESTORED; + } + else + { + *buf = XLogReadBufferExtended(rnode, forknum, blkno, mode, prefetch_buffer); + if (BufferIsValid(*buf)) + { + if (mode != RBM_ZERO_AND_LOCK && mode != RBM_ZERO_AND_CLEANUP_LOCK) + { + if (get_cleanup_lock) + LockBufferForCleanup(*buf); + else + LockBuffer(*buf, BUFFER_LOCK_EXCLUSIVE); + } + if (lsn <= PageGetLSN(BufferGetPage(*buf))) + return BLK_DONE; + else + return BLK_NEEDS_REDO; + } + else + return BLK_NOTFOUND; + } +} + +/* + * XLogReadBufferExtended + * Read a page during XLOG replay + * + * This is functionally comparable to ReadBufferExtended. There's some + * differences in the behavior wrt. the "mode" argument: + * + * In RBM_NORMAL mode, if the page doesn't exist, or contains all-zeroes, we + * return InvalidBuffer. In this case the caller should silently skip the + * update on this page. (In this situation, we expect that the page was later + * dropped or truncated. If we don't see evidence of that later in the WAL + * sequence, we'll complain at the end of WAL replay.) + * + * In RBM_ZERO_* modes, if the page doesn't exist, the relation is extended + * with all-zeroes pages up to the given block number. + * + * In RBM_NORMAL_NO_LOG mode, we return InvalidBuffer if the page doesn't + * exist, and we don't check for all-zeroes. Thus, no log entry is made + * to imply that the page should be dropped or truncated later. + * + * Optionally, recent_buffer can be used to provide a hint about the location + * of the page in the buffer pool; it does not have to be correct, but avoids + * a buffer mapping table probe if it is. + * + * NB: A redo function should normally not call this directly. To get a page + * to modify, use XLogReadBufferForRedoExtended instead. It is important that + * all pages modified by a WAL record are registered in the WAL records, or + * they will be invisible to tools that need to know which pages are modified. + */ +Buffer +XLogReadBufferExtended(RelFileNode rnode, ForkNumber forknum, + BlockNumber blkno, ReadBufferMode mode, + Buffer recent_buffer) +{ + BlockNumber lastblock; + Buffer buffer; + SMgrRelation smgr; + + Assert(blkno != P_NEW); + + /* Do we have a clue where the buffer might be already? */ + if (BufferIsValid(recent_buffer) && + mode == RBM_NORMAL && + ReadRecentBuffer(rnode, forknum, blkno, recent_buffer)) + { + buffer = recent_buffer; + goto recent_buffer_fast_path; + } + + /* Open the relation at smgr level */ + smgr = smgropen(rnode, InvalidBackendId); + + /* + * Create the target file if it doesn't already exist. This lets us cope + * if the replay sequence contains writes to a relation that is later + * deleted. (The original coding of this routine would instead suppress + * the writes, but that seems like it risks losing valuable data if the + * filesystem loses an inode during a crash. Better to write the data + * until we are actually told to delete the file.) + */ + smgrcreate(smgr, forknum, true); + + lastblock = smgrnblocks(smgr, forknum); + + if (blkno < lastblock) + { + /* page exists in file */ + buffer = ReadBufferWithoutRelcache(rnode, forknum, blkno, + mode, NULL, true); + } + else + { + /* hm, page doesn't exist in file */ + if (mode == RBM_NORMAL) + { + log_invalid_page(rnode, forknum, blkno, false); + return InvalidBuffer; + } + if (mode == RBM_NORMAL_NO_LOG) + return InvalidBuffer; + /* OK to extend the file */ + /* we do this in recovery only - no rel-extension lock needed */ + Assert(InRecovery); + buffer = InvalidBuffer; + do + { + if (buffer != InvalidBuffer) + { + if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK) + LockBuffer(buffer, BUFFER_LOCK_UNLOCK); + ReleaseBuffer(buffer); + } + buffer = ReadBufferWithoutRelcache(rnode, forknum, + P_NEW, mode, NULL, true); + } + while (BufferGetBlockNumber(buffer) < blkno); + /* Handle the corner case that P_NEW returns non-consecutive pages */ + if (BufferGetBlockNumber(buffer) != blkno) + { + if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK) + LockBuffer(buffer, BUFFER_LOCK_UNLOCK); + ReleaseBuffer(buffer); + buffer = ReadBufferWithoutRelcache(rnode, forknum, blkno, + mode, NULL, true); + } + } + +recent_buffer_fast_path: + if (mode == RBM_NORMAL) + { + /* check that page has been initialized */ + Page page = (Page) BufferGetPage(buffer); + + /* + * We assume that PageIsNew is safe without a lock. During recovery, + * there should be no other backends that could modify the buffer at + * the same time. + */ + if (PageIsNew(page)) + { + ReleaseBuffer(buffer); + log_invalid_page(rnode, forknum, blkno, true); + return InvalidBuffer; + } + } + + return buffer; +} + +/* + * Struct actually returned by CreateFakeRelcacheEntry, though the declared + * return type is Relation. + */ +typedef struct +{ + RelationData reldata; /* Note: this must be first */ + FormData_pg_class pgc; +} FakeRelCacheEntryData; + +typedef FakeRelCacheEntryData *FakeRelCacheEntry; + +/* + * Create a fake relation cache entry for a physical relation + * + * It's often convenient to use the same functions in XLOG replay as in the + * main codepath, but those functions typically work with a relcache entry. + * We don't have a working relation cache during XLOG replay, but this + * function can be used to create a fake relcache entry instead. Only the + * fields related to physical storage, like rd_rel, are initialized, so the + * fake entry is only usable in low-level operations like ReadBuffer(). + * + * This is also used for syncing WAL-skipped files. + * + * Caller must free the returned entry with FreeFakeRelcacheEntry(). + */ +Relation +CreateFakeRelcacheEntry(RelFileNode rnode) +{ + FakeRelCacheEntry fakeentry; + Relation rel; + + /* Allocate the Relation struct and all related space in one block. */ + fakeentry = palloc0(sizeof(FakeRelCacheEntryData)); + rel = (Relation) fakeentry; + + rel->rd_rel = &fakeentry->pgc; + rel->rd_node = rnode; + + /* + * We will never be working with temp rels during recovery or while + * syncing WAL-skipped files. + */ + rel->rd_backend = InvalidBackendId; + + /* It must be a permanent table here */ + rel->rd_rel->relpersistence = RELPERSISTENCE_PERMANENT; + + /* We don't know the name of the relation; use relfilenode instead */ + sprintf(RelationGetRelationName(rel), "%u", rnode.relNode); + + /* + * We set up the lockRelId in case anything tries to lock the dummy + * relation. Note that this is fairly bogus since relNode may be + * different from the relation's OID. It shouldn't really matter though. + * In recovery, we are running by ourselves and can't have any lock + * conflicts. While syncing, we already hold AccessExclusiveLock. + */ + rel->rd_lockInfo.lockRelId.dbId = rnode.dbNode; + rel->rd_lockInfo.lockRelId.relId = rnode.relNode; + + rel->rd_smgr = NULL; + + return rel; +} + +/* + * Free a fake relation cache entry. + */ +void +FreeFakeRelcacheEntry(Relation fakerel) +{ + /* make sure the fakerel is not referenced by the SmgrRelation anymore */ + if (fakerel->rd_smgr != NULL) + smgrclearowner(&fakerel->rd_smgr, fakerel->rd_smgr); + pfree(fakerel); +} + +/* + * Drop a relation during XLOG replay + * + * This is called when the relation is about to be deleted; we need to remove + * any open "invalid-page" records for the relation. + */ +void +XLogDropRelation(RelFileNode rnode, ForkNumber forknum) +{ + forget_invalid_pages(rnode, forknum, 0); +} + +/* + * Drop a whole database during XLOG replay + * + * As above, but for DROP DATABASE instead of dropping a single rel + */ +void +XLogDropDatabase(Oid dbid) +{ + /* + * This is unnecessarily heavy-handed, as it will close SMgrRelation + * objects for other databases as well. DROP DATABASE occurs seldom enough + * that it's not worth introducing a variant of smgrclose for just this + * purpose. XXX: Or should we rather leave the smgr entries dangling? + */ + smgrcloseall(); + + forget_invalid_pages_db(dbid); +} + +/* + * Truncate a relation during XLOG replay + * + * We need to clean up any open "invalid-page" records for the dropped pages. + */ +void +XLogTruncateRelation(RelFileNode rnode, ForkNumber forkNum, + BlockNumber nblocks) +{ + forget_invalid_pages(rnode, forkNum, nblocks); +} + +/* + * Determine which timeline to read an xlog page from and set the + * XLogReaderState's currTLI to that timeline ID. + * + * We care about timelines in xlogreader when we might be reading xlog + * generated prior to a promotion, either if we're currently a standby in + * recovery or if we're a promoted primary reading xlogs generated by the old + * primary before our promotion. + * + * wantPage must be set to the start address of the page to read and + * wantLength to the amount of the page that will be read, up to + * XLOG_BLCKSZ. If the amount to be read isn't known, pass XLOG_BLCKSZ. + * + * The currTLI argument should be the system-wide current timeline. + * Note that this may be different from state->currTLI, which is the timeline + * from which the caller is currently reading previous xlog records. + * + * We switch to an xlog segment from the new timeline eagerly when on a + * historical timeline, as soon as we reach the start of the xlog segment + * containing the timeline switch. The server copied the segment to the new + * timeline so all the data up to the switch point is the same, but there's no + * guarantee the old segment will still exist. It may have been deleted or + * renamed with a .partial suffix so we can't necessarily keep reading from + * the old TLI even though tliSwitchPoint says it's OK. + * + * We can't just check the timeline when we read a page on a different segment + * to the last page. We could've received a timeline switch from a cascading + * upstream, so the current segment ends abruptly (possibly getting renamed to + * .partial) and we have to switch to a new one. Even in the middle of reading + * a page we could have to dump the cached page and switch to a new TLI. + * + * Because of this, callers MAY NOT assume that currTLI is the timeline that + * will be in a page's xlp_tli; the page may begin on an older timeline or we + * might be reading from historical timeline data on a segment that's been + * copied to a new timeline. + * + * The caller must also make sure it doesn't read past the current replay + * position (using GetXLogReplayRecPtr) if executing in recovery, so it + * doesn't fail to notice that the current timeline became historical. + */ +void +XLogReadDetermineTimeline(XLogReaderState *state, XLogRecPtr wantPage, + uint32 wantLength, TimeLineID currTLI) +{ + const XLogRecPtr lastReadPage = (state->seg.ws_segno * + state->segcxt.ws_segsize + state->segoff); + + Assert(wantPage != InvalidXLogRecPtr && wantPage % XLOG_BLCKSZ == 0); + Assert(wantLength <= XLOG_BLCKSZ); + Assert(state->readLen == 0 || state->readLen <= XLOG_BLCKSZ); + Assert(currTLI != 0); + + /* + * If the desired page is currently read in and valid, we have nothing to + * do. + * + * The caller should've ensured that it didn't previously advance readOff + * past the valid limit of this timeline, so it doesn't matter if the + * current TLI has since become historical. + */ + if (lastReadPage == wantPage && + state->readLen != 0 && + lastReadPage + state->readLen >= wantPage + Min(wantLength, XLOG_BLCKSZ - 1)) + return; + + /* + * If we're reading from the current timeline, it hasn't become historical + * and the page we're reading is after the last page read, we can again + * just carry on. (Seeking backwards requires a check to make sure the + * older page isn't on a prior timeline). + * + * currTLI might've become historical since the caller obtained the value, + * but the caller is required not to read past the flush limit it saw at + * the time it looked up the timeline. There's nothing we can do about it + * if StartupXLOG() renames it to .partial concurrently. + */ + if (state->currTLI == currTLI && wantPage >= lastReadPage) + { + Assert(state->currTLIValidUntil == InvalidXLogRecPtr); + return; + } + + /* + * If we're just reading pages from a previously validated historical + * timeline and the timeline we're reading from is valid until the end of + * the current segment we can just keep reading. + */ + if (state->currTLIValidUntil != InvalidXLogRecPtr && + state->currTLI != currTLI && + state->currTLI != 0 && + ((wantPage + wantLength) / state->segcxt.ws_segsize) < + (state->currTLIValidUntil / state->segcxt.ws_segsize)) + return; + + /* + * If we reach this point we're either looking up a page for random + * access, the current timeline just became historical, or we're reading + * from a new segment containing a timeline switch. In all cases we need + * to determine the newest timeline on the segment. + * + * If it's the current timeline we can just keep reading from here unless + * we detect a timeline switch that makes the current timeline historical. + * If it's a historical timeline we can read all the segment on the newest + * timeline because it contains all the old timelines' data too. So only + * one switch check is required. + */ + { + /* + * We need to re-read the timeline history in case it's been changed + * by a promotion or replay from a cascaded replica. + */ + List *timelineHistory = readTimeLineHistory(currTLI); + XLogRecPtr endOfSegment; + + endOfSegment = ((wantPage / state->segcxt.ws_segsize) + 1) * + state->segcxt.ws_segsize - 1; + Assert(wantPage / state->segcxt.ws_segsize == + endOfSegment / state->segcxt.ws_segsize); + + /* + * Find the timeline of the last LSN on the segment containing + * wantPage. + */ + state->currTLI = tliOfPointInHistory(endOfSegment, timelineHistory); + state->currTLIValidUntil = tliSwitchPoint(state->currTLI, timelineHistory, + &state->nextTLI); + + Assert(state->currTLIValidUntil == InvalidXLogRecPtr || + wantPage + wantLength < state->currTLIValidUntil); + + list_free_deep(timelineHistory); + + elog(DEBUG3, "switched to timeline %u valid until %X/%X", + state->currTLI, + LSN_FORMAT_ARGS(state->currTLIValidUntil)); + } +} + +/* XLogReaderRoutine->segment_open callback for local pg_wal files */ +void +wal_segment_open(XLogReaderState *state, XLogSegNo nextSegNo, + TimeLineID *tli_p) +{ + TimeLineID tli = *tli_p; + char path[MAXPGPATH]; + + XLogFilePath(path, tli, nextSegNo, state->segcxt.ws_segsize); + state->seg.ws_file = BasicOpenFile(path, O_RDONLY | PG_BINARY); + if (state->seg.ws_file >= 0) + return; + + if (errno == ENOENT) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("requested WAL segment %s has already been removed", + path))); + else + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not open file \"%s\": %m", + path))); +} + +/* stock XLogReaderRoutine->segment_close callback */ +void +wal_segment_close(XLogReaderState *state) +{ + close(state->seg.ws_file); + /* need to check errno? */ + state->seg.ws_file = -1; +} + +/* + * XLogReaderRoutine->page_read callback for reading local xlog files + * + * Public because it would likely be very helpful for someone writing another + * output method outside walsender, e.g. in a bgworker. + * + * TODO: The walsender has its own version of this, but it relies on the + * walsender's latch being set whenever WAL is flushed. No such infrastructure + * exists for normal backends, so we have to do a check/sleep/repeat style of + * loop for now. + */ +int +read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, + int reqLen, XLogRecPtr targetRecPtr, char *cur_page) +{ + return read_local_xlog_page_guts(state, targetPagePtr, reqLen, + targetRecPtr, cur_page, true); +} + +/* + * Same as read_local_xlog_page except that it doesn't wait for future WAL + * to be available. + */ +int +read_local_xlog_page_no_wait(XLogReaderState *state, XLogRecPtr targetPagePtr, + int reqLen, XLogRecPtr targetRecPtr, + char *cur_page) +{ + return read_local_xlog_page_guts(state, targetPagePtr, reqLen, + targetRecPtr, cur_page, false); +} + +/* + * Implementation of read_local_xlog_page and its no wait version. + */ +static int +read_local_xlog_page_guts(XLogReaderState *state, XLogRecPtr targetPagePtr, + int reqLen, XLogRecPtr targetRecPtr, + char *cur_page, bool wait_for_wal) +{ + XLogRecPtr read_upto, + loc; + TimeLineID tli; + int count; + WALReadError errinfo; + TimeLineID currTLI; + + loc = targetPagePtr + reqLen; + + /* Loop waiting for xlog to be available if necessary */ + while (1) + { + /* + * Determine the limit of xlog we can currently read to, and what the + * most recent timeline is. + */ + if (!RecoveryInProgress()) + read_upto = GetFlushRecPtr(&currTLI); + else + read_upto = GetXLogReplayRecPtr(&currTLI); + tli = currTLI; + + /* + * Check which timeline to get the record from. + * + * We have to do it each time through the loop because if we're in + * recovery as a cascading standby, the current timeline might've + * become historical. We can't rely on RecoveryInProgress() because in + * a standby configuration like + * + * A => B => C + * + * if we're a logical decoding session on C, and B gets promoted, our + * timeline will change while we remain in recovery. + * + * We can't just keep reading from the old timeline as the last WAL + * archive in the timeline will get renamed to .partial by + * StartupXLOG(). + * + * If that happens after our caller determined the TLI but before we + * actually read the xlog page, we might still try to read from the + * old (now renamed) segment and fail. There's not much we can do + * about this, but it can only happen when we're a leaf of a cascading + * standby whose primary gets promoted while we're decoding, so a + * one-off ERROR isn't too bad. + */ + XLogReadDetermineTimeline(state, targetPagePtr, reqLen, tli); + + if (state->currTLI == currTLI) + { + + if (loc <= read_upto) + break; + + /* If asked, let's not wait for future WAL. */ + if (!wait_for_wal) + { + ReadLocalXLogPageNoWaitPrivate *private_data; + + /* + * Inform the caller of read_local_xlog_page_no_wait that the + * end of WAL has been reached. + */ + private_data = (ReadLocalXLogPageNoWaitPrivate *) + state->private_data; + private_data->end_of_wal = true; + break; + } + + CHECK_FOR_INTERRUPTS(); + pg_usleep(1000L); + } + else + { + /* + * We're on a historical timeline, so limit reading to the switch + * point where we moved to the next timeline. + * + * We don't need to GetFlushRecPtr or GetXLogReplayRecPtr. We know + * about the new timeline, so we must've received past the end of + * it. + */ + read_upto = state->currTLIValidUntil; + + /* + * Setting tli to our wanted record's TLI is slightly wrong; the + * page might begin on an older timeline if it contains a timeline + * switch, since its xlog segment will have been copied from the + * prior timeline. This is pretty harmless though, as nothing + * cares so long as the timeline doesn't go backwards. We should + * read the page header instead; FIXME someday. + */ + tli = state->currTLI; + + /* No need to wait on a historical timeline */ + break; + } + } + + if (targetPagePtr + XLOG_BLCKSZ <= read_upto) + { + /* + * more than one block available; read only that block, have caller + * come back if they need more. + */ + count = XLOG_BLCKSZ; + } + else if (targetPagePtr + reqLen > read_upto) + { + /* not enough data there */ + return -1; + } + else + { + /* enough bytes available to satisfy the request */ + count = read_upto - targetPagePtr; + } + + /* + * Even though we just determined how much of the page can be validly read + * as 'count', read the whole page anyway. It's guaranteed to be + * zero-padded up to the page boundary if it's incomplete. + */ + if (!WALRead(state, cur_page, targetPagePtr, XLOG_BLCKSZ, tli, + &errinfo)) + WALReadRaiseError(&errinfo); + + /* number of valid bytes in the buffer */ + return count; +} + +/* + * Backend-specific convenience code to handle read errors encountered by + * WALRead(). + */ +void +WALReadRaiseError(WALReadError *errinfo) +{ + WALOpenSegment *seg = &errinfo->wre_seg; + char fname[MAXFNAMELEN]; + + XLogFileName(fname, seg->ws_tli, seg->ws_segno, wal_segment_size); + + if (errinfo->wre_read < 0) + { + errno = errinfo->wre_errno; + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not read from log segment %s, offset %d: %m", + fname, errinfo->wre_off))); + } + else if (errinfo->wre_read == 0) + { + ereport(ERROR, + (errcode(ERRCODE_DATA_CORRUPTED), + errmsg("could not read from log segment %s, offset %d: read %d of %d", + fname, errinfo->wre_off, errinfo->wre_read, + errinfo->wre_req))); + } +} |