greenplumn xlogutils 源码
greenplumn xlogutils 代码
文件路径：/src/backend/access/transam/xlogutils.c
/*-------------------------------------------------------------------------
*
* 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) 2006-2008, Greenplum inc
* Portions Copyright (c) 2012-Present VMware, Inc. or its affiliates.
* Portions Copyright (c) 1996-2019, 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/xlog.h"
#include "access/xlog_internal.h"
#include "access/xlogutils.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "storage/smgr.h"
#include "utils/guc.h"
#include "utils/hsearch.h"
#include "utils/rel.h"
/*
* 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;
/* 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(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 (log_min_messages <= DEBUG1 || client_min_messages <= DEBUG1)
report_invalid_page(DEBUG1, node, forkno, blkno, present);
if (invalid_page_tab == NULL)
{
/* create hash table when first needed */
HASHCTL ctl;
memset(&ctl, 0, sizeof(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 (log_min_messages <= DEBUG2 || client_min_messages <= 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 (log_min_messages <= DEBUG2 || client_min_messages <= 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(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.
*
* 'lsn' is the LSN of the record being replayed. It is compared with 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;
Page page;
bool zeromode;
bool willinit;
if (!XLogRecGetBlockTag(record, block_id, &rnode, &forknum, &blkno))
{
/* Caller specified a bogus block_id */
elog(PANIC, "failed to locate backup block with ID %d", 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 = (record->blocks[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);
page = BufferGetPage(*buf);
if (!RestoreBlockImage(record, block_id, page))
elog(ERROR, "failed to restore block image");
/*
* 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);
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.
*
* 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 that need to know which pages are
* modified.
*/
Buffer
XLogReadBufferExtended(RelFileNode rnode, ForkNumber forknum,
BlockNumber blkno, ReadBufferMode mode)
{
BlockNumber lastblock;
Buffer buffer;
SMgrRelation smgr;
Assert(blkno != P_NEW);
/*
* Open the relation at smgr level. Relations using shared buffers need
* the default SMGR implementation.
*/
smgr = smgropen(rnode, InvalidBackendId, SMGR_MD);
/*
* 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);
}
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);
}
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);
}
}
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;
}
/*
* If the AO segment file does not exist, log the relfilenode into the
* invalid_page_table hash table using the segment file number as the block
* number to avoid creating a new hash table specifically for AO. The entry
* will be removed if there is a following xlog redo commit prepared record
* for deleting the relfilenode. The segment file number here is only used
* for a debug message since XLogDropRelation logic will remove all
* invalid_page_tab entries that have the same relfilenode and fork number.
*/
void
XLogAOSegmentFile(RelFileNode rnode, uint32 segmentFileNum)
{
log_invalid_page(rnode, MAIN_FORKNUM, segmentFileNum, false);
}
/*
* Struct actually returned by XLogFakeRelcacheEntry, 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().
*
* Caller must free the returned entry with FreeFakeRelcacheEntry().
*/
Relation
CreateFakeRelcacheEntry(RelFileNode rnode)
{
FakeRelCacheEntry fakeentry;
Relation rel;
Assert(InRecovery);
/* 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 */
rel->rd_backend = InvalidBackendId;
/* It must be a permanent table if we're in recovery. */
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,
* since we are presumably running by ourselves and can't have any lock
* conflicts ...
*/
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);
}
/*
* Read 'count' bytes from WAL into 'buf', starting at location 'startptr'
* in timeline 'tli'.
*
* Will open, and keep open, one WAL segment stored in the static file
* descriptor 'sendFile'. This means if XLogRead is used once, there will
* always be one descriptor left open until the process ends, but never
* more than one.
*
* XXX This is very similar to pg_waldump's XLogDumpXLogRead and to XLogRead
* in walsender.c but for small differences (such as lack of elog() in
* frontend). Probably these should be merged at some point.
*/
static void
XLogRead(char *buf, int segsize, TimeLineID tli, XLogRecPtr startptr,
Size count)
{
char *p;
XLogRecPtr recptr;
Size nbytes;
/* state maintained across calls */
static int sendFile = -1;
static XLogSegNo sendSegNo = 0;
static TimeLineID sendTLI = 0;
static uint32 sendOff = 0;
Assert(segsize == wal_segment_size);
p = buf;
recptr = startptr;
nbytes = count;
while (nbytes > 0)
{
uint32 startoff;
int segbytes;
int readbytes;
startoff = XLogSegmentOffset(recptr, segsize);
/* Do we need to switch to a different xlog segment? */
if (sendFile < 0 || !XLByteInSeg(recptr, sendSegNo, segsize) ||
sendTLI != tli)
{
char path[MAXPGPATH];
if (sendFile >= 0)
close(sendFile);
XLByteToSeg(recptr, sendSegNo, segsize);
XLogFilePath(path, tli, sendSegNo, segsize);
sendFile = BasicOpenFile(path, O_RDONLY | PG_BINARY);
if (sendFile < 0)
{
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)));
}
sendOff = 0;
sendTLI = tli;
}
/* Need to seek in the file? */
if (sendOff != startoff)
{
if (lseek(sendFile, (off_t) startoff, SEEK_SET) < 0)
{
char path[MAXPGPATH];
int save_errno = errno;
XLogFilePath(path, tli, sendSegNo, segsize);
errno = save_errno;
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek in log segment %s to offset %u: %m",
path, startoff)));
}
sendOff = startoff;
}
/* How many bytes are within this segment? */
if (nbytes > (segsize - startoff))
segbytes = segsize - startoff;
else
segbytes = nbytes;
pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
readbytes = read(sendFile, p, segbytes);
pgstat_report_wait_end();
if (readbytes <= 0)
{
char path[MAXPGPATH];
int save_errno = errno;
XLogFilePath(path, tli, sendSegNo, segsize);
errno = save_errno;
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from log segment %s, offset %u, length %lu: %m",
path, sendOff, (unsigned long) segbytes)));
}
/* Update state for read */
recptr += readbytes;
sendOff += readbytes;
nbytes -= readbytes;
p += readbytes;
}
}
/*
* 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 master reading xlogs generated by the old
* master 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.
*
* 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 GetWalRcvWriteRecPtr) if executing in recovery, so it
* doesn't fail to notice that the current timeline became historical. The
* caller must also update ThisTimeLineID with the result of
* GetWalRcvWriteRecPtr and must check RecoveryInProgress().
*/
void
XLogReadDetermineTimeline(XLogReaderState *state, XLogRecPtr wantPage, uint32 wantLength)
{
const XLogRecPtr lastReadPage = state->readSegNo *
state->wal_segment_size + state->readOff;
Assert(wantPage != InvalidXLogRecPtr && wantPage % XLOG_BLCKSZ == 0);
Assert(wantLength <= XLOG_BLCKSZ);
Assert(state->readLen == 0 || state->readLen <= XLOG_BLCKSZ);
/*
* 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).
*
* ThisTimeLineID might've become historical since we last looked, 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 == ThisTimeLineID && 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 != ThisTimeLineID &&
state->currTLI != 0 &&
((wantPage + wantLength) / state->wal_segment_size) <
(state->currTLIValidUntil / state->wal_segment_size))
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(ThisTimeLineID);
XLogRecPtr endOfSegment = (((wantPage / state->wal_segment_size) + 1)
* state->wal_segment_size) - 1;
Assert(wantPage / state->wal_segment_size ==
endOfSegment / state->wal_segment_size);
/*
* 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,
(uint32) (state->currTLIValidUntil >> 32),
(uint32) (state->currTLIValidUntil));
}
}
/*
* read_page 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,
TimeLineID *pageTLI)
{
XLogRecPtr read_upto,
loc;
int count;
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.
*
* RecoveryInProgress() will update ThisTimeLineID when it first
* notices recovery finishes, so we only have to maintain it for the
* local process until recovery ends.
*/
if (!RecoveryInProgress())
read_upto = GetFlushRecPtr();
else
read_upto = GetXLogReplayRecPtr(&ThisTimeLineID);
*pageTLI = ThisTimeLineID;
/*
* 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 updated ThisTimeLineID 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 master gets promoted while we're decoding, so a
* one-off ERROR isn't too bad.
*/
XLogReadDetermineTimeline(state, targetPagePtr, reqLen);
if (state->currTLI == ThisTimeLineID)
{
if (loc <= read_upto)
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 pageTLI 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.
*/
*pageTLI = state->currTLI;
/* No need to wait on a historical timeline */
break;
}
}
/* more than one block available */
if (targetPagePtr + XLOG_BLCKSZ <= read_upto)
count = XLOG_BLCKSZ;
/* not enough data there */
else if (targetPagePtr + reqLen > read_upto)
return -1;
/* part of the page available */
else
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.
*/
XLogRead(cur_page, state->wal_segment_size, *pageTLI, targetPagePtr,
XLOG_BLCKSZ);
return count;
}
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