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postgresql/src/backend/postmaster/walsummarizer.c

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/*-------------------------------------------------------------------------
*
* walsummarizer.c
*
* Background process to perform WAL summarization, if it is enabled.
* It continuously scans the write-ahead log and periodically emits a
* summary file which indicates which blocks in which relation forks
* were modified by WAL records in the LSN range covered by the summary
* file. See walsummary.c and blkreftable.c for more details on the
* naming and contents of WAL summary files.
*
* If configured to do, this background process will also remove WAL
* summary files when the file timestamp is older than a configurable
* threshold (but only if the WAL has been removed first).
*
* Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
*
* IDENTIFICATION
* src/backend/postmaster/walsummarizer.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/timeline.h"
#include "access/xlog.h"
#include "access/xlog_internal.h"
#include "access/xlogrecovery.h"
#include "access/xlogutils.h"
#include "backup/walsummary.h"
#include "catalog/storage_xlog.h"
#include "commands/dbcommands_xlog.h"
#include "common/blkreftable.h"
#include "libpq/pqsignal.h"
#include "miscadmin.h"
#include "postmaster/interrupt.h"
#include "postmaster/walsummarizer.h"
#include "replication/walreceiver.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/latch.h"
#include "storage/lwlock.h"
#include "storage/proc.h"
#include "storage/procsignal.h"
#include "storage/shmem.h"
#include "utils/guc.h"
#include "utils/memutils.h"
#include "utils/wait_event.h"
/*
* Data in shared memory related to WAL summarization.
*/
typedef struct
{
/*
* These fields are protected by WALSummarizerLock.
*
* Until we've discovered what summary files already exist on disk and
* stored that information in shared memory, initialized is false and the
* other fields here contain no meaningful information. After that has
* been done, initialized is true.
*
* summarized_tli and summarized_lsn indicate the last LSN and TLI at
* which the next summary file will start. Normally, these are the LSN and
* TLI at which the last file ended; in such case, lsn_is_exact is true.
* If, however, the LSN is just an approximation, then lsn_is_exact is
* false. This can happen if, for example, there are no existing WAL
* summary files at startup. In that case, we have to derive the position
* at which to start summarizing from the WAL files that exist on disk,
* and so the LSN might point to the start of the next file even though
* that might happen to be in the middle of a WAL record.
*
* summarizer_pgprocno is the proc number of the summarizer process, if
* one is running, or else INVALID_PROC_NUMBER.
*
* pending_lsn is used by the summarizer to advertise the ending LSN of a
* record it has recently read. It shouldn't ever be less than
* summarized_lsn, but might be greater, because the summarizer buffers
* data for a range of LSNs in memory before writing out a new file.
*/
bool initialized;
TimeLineID summarized_tli;
XLogRecPtr summarized_lsn;
bool lsn_is_exact;
ProcNumber summarizer_pgprocno;
XLogRecPtr pending_lsn;
/*
* This field handles its own synchronization.
*/
ConditionVariable summary_file_cv;
} WalSummarizerData;
/*
* Private data for our xlogreader's page read callback.
*/
typedef struct
{
TimeLineID tli;
bool historic;
XLogRecPtr read_upto;
bool end_of_wal;
} SummarizerReadLocalXLogPrivate;
/* Pointer to shared memory state. */
static WalSummarizerData *WalSummarizerCtl;
/*
* When we reach end of WAL and need to read more, we sleep for a number of
* milliseconds that is a integer multiple of MS_PER_SLEEP_QUANTUM. This is
* the multiplier. It should vary between 1 and MAX_SLEEP_QUANTA, depending
* on system activity. See summarizer_wait_for_wal() for how we adjust this.
*/
static long sleep_quanta = 1;
/*
* The sleep time will always be a multiple of 200ms and will not exceed
* thirty seconds (150 * 200 = 30 * 1000). Note that the timeout here needs
* to be substantially less than the maximum amount of time for which an
* incremental backup will wait for this process to catch up. Otherwise, an
* incremental backup might time out on an idle system just because we sleep
* for too long.
*/
#define MAX_SLEEP_QUANTA 150
#define MS_PER_SLEEP_QUANTUM 200
/*
* This is a count of the number of pages of WAL that we've read since the
* last time we waited for more WAL to appear.
*/
static long pages_read_since_last_sleep = 0;
/*
* Most recent RedoRecPtr value observed by MaybeRemoveOldWalSummaries.
*/
static XLogRecPtr redo_pointer_at_last_summary_removal = InvalidXLogRecPtr;
/*
* GUC parameters
*/
bool summarize_wal = false;
int wal_summary_keep_time = 10 * 24 * 60;
static void WalSummarizerShutdown(int code, Datum arg);
static XLogRecPtr GetLatestLSN(TimeLineID *tli);
static void HandleWalSummarizerInterrupts(void);
static XLogRecPtr SummarizeWAL(TimeLineID tli, XLogRecPtr start_lsn,
bool exact, XLogRecPtr switch_lsn,
XLogRecPtr maximum_lsn);
static void SummarizeDbaseRecord(XLogReaderState *xlogreader,
BlockRefTable *brtab);
static void SummarizeSmgrRecord(XLogReaderState *xlogreader,
BlockRefTable *brtab);
static void SummarizeXactRecord(XLogReaderState *xlogreader,
BlockRefTable *brtab);
static bool SummarizeXlogRecord(XLogReaderState *xlogreader);
static int summarizer_read_local_xlog_page(XLogReaderState *state,
XLogRecPtr targetPagePtr,
int reqLen,
XLogRecPtr targetRecPtr,
char *cur_page);
static void summarizer_wait_for_wal(void);
static void MaybeRemoveOldWalSummaries(void);
/*
* Amount of shared memory required for this module.
*/
Size
WalSummarizerShmemSize(void)
{
return sizeof(WalSummarizerData);
}
/*
* Create or attach to shared memory segment for this module.
*/
void
WalSummarizerShmemInit(void)
{
bool found;
WalSummarizerCtl = (WalSummarizerData *)
ShmemInitStruct("Wal Summarizer Ctl", WalSummarizerShmemSize(),
&found);
if (!found)
{
/*
* First time through, so initialize.
*
* We're just filling in dummy values here -- the real initialization
* will happen when GetOldestUnsummarizedLSN() is called for the first
* time.
*/
WalSummarizerCtl->initialized = false;
WalSummarizerCtl->summarized_tli = 0;
WalSummarizerCtl->summarized_lsn = InvalidXLogRecPtr;
WalSummarizerCtl->lsn_is_exact = false;
WalSummarizerCtl->summarizer_pgprocno = INVALID_PROC_NUMBER;
WalSummarizerCtl->pending_lsn = InvalidXLogRecPtr;
ConditionVariableInit(&WalSummarizerCtl->summary_file_cv);
}
}
/*
* Entry point for walsummarizer process.
*/
void
WalSummarizerMain(void)
{
sigjmp_buf local_sigjmp_buf;
MemoryContext context;
/*
* Within this function, 'current_lsn' and 'current_tli' refer to the
* point from which the next WAL summary file should start. 'exact' is
* true if 'current_lsn' is known to be the start of a WAL record or WAL
* segment, and false if it might be in the middle of a record someplace.
*
* 'switch_lsn' and 'switch_tli', if set, are the LSN at which we need to
* switch to a new timeline and the timeline to which we need to switch.
* If not set, we either haven't figured out the answers yet or we're
* already on the latest timeline.
*/
XLogRecPtr current_lsn;
TimeLineID current_tli;
bool exact;
XLogRecPtr switch_lsn = InvalidXLogRecPtr;
TimeLineID switch_tli = 0;
ereport(DEBUG1,
(errmsg_internal("WAL summarizer started")));
/*
* Properly accept or ignore signals the postmaster might send us
*
* We have no particular use for SIGINT at the moment, but seems
* reasonable to treat like SIGTERM.
*/
pqsignal(SIGHUP, SignalHandlerForConfigReload);
pqsignal(SIGINT, SignalHandlerForShutdownRequest);
pqsignal(SIGTERM, SignalHandlerForShutdownRequest);
/* SIGQUIT handler was already set up by InitPostmasterChild */
pqsignal(SIGALRM, SIG_IGN);
pqsignal(SIGPIPE, SIG_IGN);
pqsignal(SIGUSR1, procsignal_sigusr1_handler);
pqsignal(SIGUSR2, SIG_IGN); /* not used */
/* Advertise ourselves. */
on_shmem_exit(WalSummarizerShutdown, (Datum) 0);
LWLockAcquire(WALSummarizerLock, LW_EXCLUSIVE);
WalSummarizerCtl->summarizer_pgprocno = MyProcNumber;
LWLockRelease(WALSummarizerLock);
/* Create and switch to a memory context that we can reset on error. */
context = AllocSetContextCreate(TopMemoryContext,
"Wal Summarizer",
ALLOCSET_DEFAULT_SIZES);
MemoryContextSwitchTo(context);
/*
* Reset some signals that are accepted by postmaster but not here
*/
pqsignal(SIGCHLD, SIG_DFL);
/*
* If an exception is encountered, processing resumes here.
*/
if (sigsetjmp(local_sigjmp_buf, 1) != 0)
{
/* Since not using PG_TRY, must reset error stack by hand */
error_context_stack = NULL;
/* Prevent interrupts while cleaning up */
HOLD_INTERRUPTS();
/* Report the error to the server log */
EmitErrorReport();
/* Release resources we might have acquired. */
LWLockReleaseAll();
ConditionVariableCancelSleep();
pgstat_report_wait_end();
ReleaseAuxProcessResources(false);
AtEOXact_Files(false);
AtEOXact_HashTables(false);
/*
* Now return to normal top-level context and clear ErrorContext for
* next time.
*/
MemoryContextSwitchTo(context);
FlushErrorState();
/* Flush any leaked data in the top-level context */
MemoryContextReset(context);
/* Now we can allow interrupts again */
RESUME_INTERRUPTS();
/*
* Sleep for 10 seconds before attempting to resume operations in
* order to avoid excessive logging.
*
* Many of the likely error conditions are things that will repeat
* every time. For example, if the WAL can't be read or the summary
* can't be written, only administrator action will cure the problem.
* So a really fast retry time doesn't seem to be especially
* beneficial, and it will clutter the logs.
*/
(void) WaitLatch(MyLatch,
WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
10000,
WAIT_EVENT_WAL_SUMMARIZER_ERROR);
}
/* We can now handle ereport(ERROR) */
PG_exception_stack = &local_sigjmp_buf;
/*
* Unblock signals (they were blocked when the postmaster forked us)
*/
sigprocmask(SIG_SETMASK, &UnBlockSig, NULL);
/*
* Fetch information about previous progress from shared memory, and ask
* GetOldestUnsummarizedLSN to reset pending_lsn to summarized_lsn. We
* might be recovering from an error, and if so, pending_lsn might have
* advanced past summarized_lsn, but any WAL we read previously has been
* lost and will need to be reread.
*
* If we discover that WAL summarization is not enabled, just exit.
*/
current_lsn = GetOldestUnsummarizedLSN(&current_tli, &exact, true);
if (XLogRecPtrIsInvalid(current_lsn))
proc_exit(0);
/*
* Loop forever
*/
for (;;)
{
XLogRecPtr latest_lsn;
TimeLineID latest_tli;
XLogRecPtr end_of_summary_lsn;
/* Flush any leaked data in the top-level context */
MemoryContextReset(context);
/* Process any signals received recently. */
HandleWalSummarizerInterrupts();
/* If it's time to remove any old WAL summaries, do that now. */
MaybeRemoveOldWalSummaries();
/* Find the LSN and TLI up to which we can safely summarize. */
latest_lsn = GetLatestLSN(&latest_tli);
/*
* If we're summarizing a historic timeline and we haven't yet
* computed the point at which to switch to the next timeline, do that
* now.
*
* Note that if this is a standby, what was previously the current
* timeline could become historic at any time.
*
* We could try to make this more efficient by caching the results of
* readTimeLineHistory when latest_tli has not changed, but since we
* only have to do this once per timeline switch, we probably wouldn't
* save any significant amount of work in practice.
*/
if (current_tli != latest_tli && XLogRecPtrIsInvalid(switch_lsn))
{
List *tles = readTimeLineHistory(latest_tli);
switch_lsn = tliSwitchPoint(current_tli, tles, &switch_tli);
ereport(DEBUG1,
errmsg("switch point from TLI %u to TLI %u is at %X/%X",
current_tli, switch_tli, LSN_FORMAT_ARGS(switch_lsn)));
}
/*
* If we've reached the switch LSN, we can't summarize anything else
* on this timeline. Switch to the next timeline and go around again.
*/
if (!XLogRecPtrIsInvalid(switch_lsn) && current_lsn >= switch_lsn)
{
current_tli = switch_tli;
switch_lsn = InvalidXLogRecPtr;
switch_tli = 0;
continue;
}
/* Summarize WAL. */
end_of_summary_lsn = SummarizeWAL(current_tli,
current_lsn, exact,
switch_lsn, latest_lsn);
Assert(!XLogRecPtrIsInvalid(end_of_summary_lsn));
Assert(end_of_summary_lsn >= current_lsn);
/*
* Update state for next loop iteration.
*
* Next summary file should start from exactly where this one ended.
*/
current_lsn = end_of_summary_lsn;
exact = true;
/* Update state in shared memory. */
LWLockAcquire(WALSummarizerLock, LW_EXCLUSIVE);
Assert(WalSummarizerCtl->pending_lsn <= end_of_summary_lsn);
WalSummarizerCtl->summarized_lsn = end_of_summary_lsn;
WalSummarizerCtl->summarized_tli = current_tli;
WalSummarizerCtl->lsn_is_exact = true;
WalSummarizerCtl->pending_lsn = end_of_summary_lsn;
LWLockRelease(WALSummarizerLock);
/* Wake up anyone waiting for more summary files to be written. */
ConditionVariableBroadcast(&WalSummarizerCtl->summary_file_cv);
}
}
/*
* Get information about the state of the WAL summarizer.
*/
void
GetWalSummarizerState(TimeLineID *summarized_tli, XLogRecPtr *summarized_lsn,
XLogRecPtr *pending_lsn, int *summarizer_pid)
{
LWLockAcquire(WALSummarizerLock, LW_SHARED);
if (!WalSummarizerCtl->initialized)
{
/*
* If initialized is false, the rest of the structure contents are
* undefined.
*/
*summarized_tli = 0;
*summarized_lsn = InvalidXLogRecPtr;
*pending_lsn = InvalidXLogRecPtr;
*summarizer_pid = -1;
}
else
{
int summarizer_pgprocno = WalSummarizerCtl->summarizer_pgprocno;
*summarized_tli = WalSummarizerCtl->summarized_tli;
*summarized_lsn = WalSummarizerCtl->summarized_lsn;
if (summarizer_pgprocno == INVALID_PROC_NUMBER)
{
/*
* If the summarizer has exited, the fact that it had processed
* beyond summarized_lsn is irrelevant now.
*/
*pending_lsn = WalSummarizerCtl->summarized_lsn;
*summarizer_pid = -1;
}
else
{
*pending_lsn = WalSummarizerCtl->pending_lsn;
/*
* We're not fussed about inexact answers here, since they could
* become stale instantly, so we don't bother taking the lock, but
* make sure that invalid PID values are normalized to -1.
*/
*summarizer_pid = GetPGProcByNumber(summarizer_pgprocno)->pid;
if (*summarizer_pid <= 0)
*summarizer_pid = -1;
}
}
LWLockRelease(WALSummarizerLock);
}
/*
* Get the oldest LSN in this server's timeline history that has not yet been
* summarized.
*
* If *tli != NULL, it will be set to the TLI for the LSN that is returned.
*
* If *lsn_is_exact != NULL, it will be set to true if the returned LSN is
* necessarily the start of a WAL record and false if it's just the beginning
* of a WAL segment.
*
* If reset_pending_lsn is true, resets the pending_lsn in shared memory to
* be equal to the summarized_lsn.
*/
XLogRecPtr
GetOldestUnsummarizedLSN(TimeLineID *tli, bool *lsn_is_exact,
bool reset_pending_lsn)
{
TimeLineID latest_tli;
LWLockMode mode = reset_pending_lsn ? LW_EXCLUSIVE : LW_SHARED;
int n;
List *tles;
XLogRecPtr unsummarized_lsn = InvalidXLogRecPtr;
TimeLineID unsummarized_tli = 0;
bool should_make_exact = false;
List *existing_summaries;
ListCell *lc;
/* If not summarizing WAL, do nothing. */
if (!summarize_wal)
return InvalidXLogRecPtr;
/*
* Unless we need to reset the pending_lsn, we initially acquire the lock
* in shared mode and try to fetch the required information. If we acquire
* in shared mode and find that the data structure hasn't been
* initialized, we reacquire the lock in exclusive mode so that we can
* initialize it. However, if someone else does that first before we get
* the lock, then we can just return the requested information after all.
*/
while (1)
{
LWLockAcquire(WALSummarizerLock, mode);
if (WalSummarizerCtl->initialized)
{
unsummarized_lsn = WalSummarizerCtl->summarized_lsn;
if (tli != NULL)
*tli = WalSummarizerCtl->summarized_tli;
if (lsn_is_exact != NULL)
*lsn_is_exact = WalSummarizerCtl->lsn_is_exact;
if (reset_pending_lsn)
WalSummarizerCtl->pending_lsn =
WalSummarizerCtl->summarized_lsn;
LWLockRelease(WALSummarizerLock);
return unsummarized_lsn;
}
if (mode == LW_EXCLUSIVE)
break;
LWLockRelease(WALSummarizerLock);
mode = LW_EXCLUSIVE;
}
/*
* The data structure needs to be initialized, and we are the first to
* obtain the lock in exclusive mode, so it's our job to do that
* initialization.
*
* So, find the oldest timeline on which WAL still exists, and the
* earliest segment for which it exists.
*/
(void) GetLatestLSN(&latest_tli);
tles = readTimeLineHistory(latest_tli);
for (n = list_length(tles) - 1; n >= 0; --n)
{
TimeLineHistoryEntry *tle = list_nth(tles, n);
XLogSegNo oldest_segno;
oldest_segno = XLogGetOldestSegno(tle->tli);
if (oldest_segno != 0)
{
/* Compute oldest LSN that still exists on disk. */
XLogSegNoOffsetToRecPtr(oldest_segno, 0, wal_segment_size,
unsummarized_lsn);
unsummarized_tli = tle->tli;
break;
}
}
/* It really should not be possible for us to find no WAL. */
if (unsummarized_tli == 0)
ereport(ERROR,
errcode(ERRCODE_INTERNAL_ERROR),
errmsg_internal("no WAL found on timeline %u", latest_tli));
/*
* Don't try to summarize anything older than the end LSN of the newest
* summary file that exists for this timeline.
*/
existing_summaries =
GetWalSummaries(unsummarized_tli,
InvalidXLogRecPtr, InvalidXLogRecPtr);
foreach(lc, existing_summaries)
{
WalSummaryFile *ws = lfirst(lc);
if (ws->end_lsn > unsummarized_lsn)
{
unsummarized_lsn = ws->end_lsn;
should_make_exact = true;
}
}
/* Update shared memory with the discovered values. */
WalSummarizerCtl->initialized = true;
WalSummarizerCtl->summarized_lsn = unsummarized_lsn;
WalSummarizerCtl->summarized_tli = unsummarized_tli;
WalSummarizerCtl->lsn_is_exact = should_make_exact;
WalSummarizerCtl->pending_lsn = unsummarized_lsn;
/* Also return the to the caller as required. */
if (tli != NULL)
*tli = WalSummarizerCtl->summarized_tli;
if (lsn_is_exact != NULL)
*lsn_is_exact = WalSummarizerCtl->lsn_is_exact;
LWLockRelease(WALSummarizerLock);
return unsummarized_lsn;
}
/*
* Attempt to set the WAL summarizer's latch.
*
* This might not work, because there's no guarantee that the WAL summarizer
* process was successfully started, and it also might have started but
* subsequently terminated. So, under normal circumstances, this will get the
* latch set, but there's no guarantee.
*/
void
SetWalSummarizerLatch(void)
{
ProcNumber pgprocno;
if (WalSummarizerCtl == NULL)
return;
LWLockAcquire(WALSummarizerLock, LW_EXCLUSIVE);
pgprocno = WalSummarizerCtl->summarizer_pgprocno;
LWLockRelease(WALSummarizerLock);
if (pgprocno != INVALID_PROC_NUMBER)
SetLatch(&ProcGlobal->allProcs[pgprocno].procLatch);
}
/*
* Wait until WAL summarization reaches the given LSN, but not longer than
* the given timeout.
*
* The return value is the first still-unsummarized LSN. If it's greater than
* or equal to the passed LSN, then that LSN was reached. If not, we timed out.
*
* Either way, *pending_lsn is set to the value taken from WalSummarizerCtl.
*/
XLogRecPtr
WaitForWalSummarization(XLogRecPtr lsn, long timeout, XLogRecPtr *pending_lsn)
{
TimestampTz start_time = GetCurrentTimestamp();
TimestampTz deadline = TimestampTzPlusMilliseconds(start_time, timeout);
XLogRecPtr summarized_lsn;
Assert(!XLogRecPtrIsInvalid(lsn));
Assert(timeout > 0);
while (1)
{
TimestampTz now;
long remaining_timeout;
/*
* If the LSN summarized on disk has reached the target value, stop.
*/
LWLockAcquire(WALSummarizerLock, LW_EXCLUSIVE);
summarized_lsn = WalSummarizerCtl->summarized_lsn;
*pending_lsn = WalSummarizerCtl->pending_lsn;
LWLockRelease(WALSummarizerLock);
if (summarized_lsn >= lsn)
break;
/* Timeout reached? If yes, stop. */
now = GetCurrentTimestamp();
remaining_timeout = TimestampDifferenceMilliseconds(now, deadline);
if (remaining_timeout <= 0)
break;
/* Wait and see. */
ConditionVariableTimedSleep(&WalSummarizerCtl->summary_file_cv,
remaining_timeout,
WAIT_EVENT_WAL_SUMMARY_READY);
}
return summarized_lsn;
}
/*
* On exit, update shared memory to make it clear that we're no longer
* running.
*/
static void
WalSummarizerShutdown(int code, Datum arg)
{
LWLockAcquire(WALSummarizerLock, LW_EXCLUSIVE);
WalSummarizerCtl->summarizer_pgprocno = INVALID_PROC_NUMBER;
LWLockRelease(WALSummarizerLock);
}
/*
* Get the latest LSN that is eligible to be summarized, and set *tli to the
* corresponding timeline.
*/
static XLogRecPtr
GetLatestLSN(TimeLineID *tli)
{
if (!RecoveryInProgress())
{
/* Don't summarize WAL before it's flushed. */
return GetFlushRecPtr(tli);
}
else
{
XLogRecPtr flush_lsn;
TimeLineID flush_tli;
XLogRecPtr replay_lsn;
TimeLineID replay_tli;
/*
* What we really want to know is how much WAL has been flushed to
* disk, but the only flush position available is the one provided by
* the walreceiver, which may not be running, because this could be
* crash recovery or recovery via restore_command. So use either the
* WAL receiver's flush position or the replay position, whichever is
* further ahead, on the theory that if the WAL has been replayed then
* it must also have been flushed to disk.
*/
flush_lsn = GetWalRcvFlushRecPtr(NULL, &flush_tli);
replay_lsn = GetXLogReplayRecPtr(&replay_tli);
if (flush_lsn > replay_lsn)
{
*tli = flush_tli;
return flush_lsn;
}
else
{
*tli = replay_tli;
return replay_lsn;
}
}
}
/*
* Interrupt handler for main loop of WAL summarizer process.
*/
static void
HandleWalSummarizerInterrupts(void)
{
if (ProcSignalBarrierPending)
ProcessProcSignalBarrier();
if (ConfigReloadPending)
{
ConfigReloadPending = false;
ProcessConfigFile(PGC_SIGHUP);
}
if (ShutdownRequestPending || !summarize_wal)
{
ereport(DEBUG1,
errmsg_internal("WAL summarizer shutting down"));
proc_exit(0);
}
/* Perform logging of memory contexts of this process */
if (LogMemoryContextPending)
ProcessLogMemoryContextInterrupt();
}
/*
* Summarize a range of WAL records on a single timeline.
*
* 'tli' is the timeline to be summarized.
*
* 'start_lsn' is the point at which we should start summarizing. If this
* value comes from the end LSN of the previous record as returned by the
* xlogreader machinery, 'exact' should be true; otherwise, 'exact' should
* be false, and this function will search forward for the start of a valid
* WAL record.
*
* 'switch_lsn' is the point at which we should switch to a later timeline,
* if we're summarizing a historic timeline.
*
* 'maximum_lsn' identifies the point beyond which we can't count on being
* able to read any more WAL. It should be the switch point when reading a
* historic timeline, or the most-recently-measured end of WAL when reading
* the current timeline.
*
* The return value is the LSN at which the WAL summary actually ends. Most
* often, a summary file ends because we notice that a checkpoint has
* occurred and reach the redo pointer of that checkpoint, but sometimes
* we stop for other reasons, such as a timeline switch.
*/
static XLogRecPtr
SummarizeWAL(TimeLineID tli, XLogRecPtr start_lsn, bool exact,
XLogRecPtr switch_lsn, XLogRecPtr maximum_lsn)
{
SummarizerReadLocalXLogPrivate *private_data;
XLogReaderState *xlogreader;
XLogRecPtr summary_start_lsn;
XLogRecPtr summary_end_lsn = switch_lsn;
char temp_path[MAXPGPATH];
char final_path[MAXPGPATH];
WalSummaryIO io;
BlockRefTable *brtab = CreateEmptyBlockRefTable();
/* Initialize private data for xlogreader. */
private_data = (SummarizerReadLocalXLogPrivate *)
palloc0(sizeof(SummarizerReadLocalXLogPrivate));
private_data->tli = tli;
private_data->historic = !XLogRecPtrIsInvalid(switch_lsn);
private_data->read_upto = maximum_lsn;
/* Create xlogreader. */
xlogreader = XLogReaderAllocate(wal_segment_size, NULL,
XL_ROUTINE(.page_read = &summarizer_read_local_xlog_page,
.segment_open = &wal_segment_open,
.segment_close = &wal_segment_close),
private_data);
if (xlogreader == NULL)
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
errmsg("out of memory"),
errdetail("Failed while allocating a WAL reading processor.")));
/*
* When exact = false, we're starting from an arbitrary point in the WAL
* and must search forward for the start of the next record.
*
* When exact = true, start_lsn should be either the LSN where a record
* begins, or the LSN of a page where the page header is immediately
* followed by the start of a new record. XLogBeginRead should tolerate
* either case.
*
* We need to allow for both cases because the behavior of xlogreader
* varies. When a record spans two or more xlog pages, the ending LSN
* reported by xlogreader will be the starting LSN of the following
* record, but when an xlog page boundary falls between two records, the
* end LSN for the first will be reported as the first byte of the
* following page. We can't know until we read that page how large the
* header will be, but we'll have to skip over it to find the next record.
*/
if (exact)
{
/*
* Even if start_lsn is the beginning of a page rather than the
* beginning of the first record on that page, we should still use it
* as the start LSN for the summary file. That's because we detect
* missing summary files by looking for cases where the end LSN of one
* file is less than the start LSN of the next file. When only a page
* header is skipped, nothing has been missed.
*/
XLogBeginRead(xlogreader, start_lsn);
summary_start_lsn = start_lsn;
}
else
{
summary_start_lsn = XLogFindNextRecord(xlogreader, start_lsn);
if (XLogRecPtrIsInvalid(summary_start_lsn))
{
/*
* If we hit end-of-WAL while trying to find the next valid
* record, we must be on a historic timeline that has no valid
* records that begin after start_lsn and before end of WAL.
*/
if (private_data->end_of_wal)
{
ereport(DEBUG1,
errmsg_internal("could not read WAL from timeline %u at %X/%X: end of WAL at %X/%X",
tli,
LSN_FORMAT_ARGS(start_lsn),
LSN_FORMAT_ARGS(private_data->read_upto)));
/*
* The timeline ends at or after start_lsn, without containing
* any records. Thus, we must make sure the main loop does not
* iterate. If start_lsn is the end of the timeline, then we
* won't actually emit an empty summary file, but otherwise,
* we must, to capture the fact that the LSN range in question
* contains no interesting WAL records.
*/
summary_start_lsn = start_lsn;
summary_end_lsn = private_data->read_upto;
switch_lsn = xlogreader->EndRecPtr;
}
else
ereport(ERROR,
(errmsg("could not find a valid record after %X/%X",
LSN_FORMAT_ARGS(start_lsn))));
}
/* We shouldn't go backward. */
Assert(summary_start_lsn >= start_lsn);
}
/*
* Main loop: read xlog records one by one.
*/
while (1)
{
int block_id;
char *errormsg;
XLogRecord *record;
bool stop_requested = false;
HandleWalSummarizerInterrupts();
/* We shouldn't go backward. */
Assert(summary_start_lsn <= xlogreader->EndRecPtr);
/* Now read the next record. */
record = XLogReadRecord(xlogreader, &errormsg);
if (record == NULL)
{
if (private_data->end_of_wal)
{
/*
* This timeline must be historic and must end before we were
* able to read a complete record.
*/
ereport(DEBUG1,
errmsg_internal("could not read WAL from timeline %u at %X/%X: end of WAL at %X/%X",
tli,
LSN_FORMAT_ARGS(xlogreader->EndRecPtr),
LSN_FORMAT_ARGS(private_data->read_upto)));
/* Summary ends at end of WAL. */
summary_end_lsn = private_data->read_upto;
break;
}
if (errormsg)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read WAL from timeline %u at %X/%X: %s",
tli, LSN_FORMAT_ARGS(xlogreader->EndRecPtr),
errormsg)));
else
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read WAL from timeline %u at %X/%X",
tli, LSN_FORMAT_ARGS(xlogreader->EndRecPtr))));
}
/* We shouldn't go backward. */
Assert(summary_start_lsn <= xlogreader->EndRecPtr);
if (!XLogRecPtrIsInvalid(switch_lsn) &&
xlogreader->ReadRecPtr >= switch_lsn)
{
/*
* Whoops! We've read a record that *starts* after the switch LSN,
* contrary to our goal of reading only until we hit the first
* record that ends at or after the switch LSN. Pretend we didn't
* read it after all by bailing out of this loop right here,
* before we do anything with this record.
*
* This can happen because the last record before the switch LSN
* might be continued across multiple pages, and then we might
* come to a page with XLP_FIRST_IS_OVERWRITE_CONTRECORD set. In
* that case, the record that was continued across multiple pages
* is incomplete and will be disregarded, and the read will
* restart from the beginning of the page that is flagged
* XLP_FIRST_IS_OVERWRITE_CONTRECORD.
*
* If this case occurs, we can fairly say that the current summary
* file ends at the switch LSN exactly. The first record on the
* page marked XLP_FIRST_IS_OVERWRITE_CONTRECORD will be
* discovered when generating the next summary file.
*/
summary_end_lsn = switch_lsn;
break;
}
/* Special handling for particular types of WAL records. */
switch (XLogRecGetRmid(xlogreader))
{
case RM_DBASE_ID:
SummarizeDbaseRecord(xlogreader, brtab);
break;
case RM_SMGR_ID:
SummarizeSmgrRecord(xlogreader, brtab);
break;
case RM_XACT_ID:
SummarizeXactRecord(xlogreader, brtab);
break;
case RM_XLOG_ID:
stop_requested = SummarizeXlogRecord(xlogreader);
break;
default:
break;
}
/*
* If we've been told that it's time to end this WAL summary file, do
* so. As an exception, if there's nothing included in this WAL
* summary file yet, then stopping doesn't make any sense, and we
* should wait until the next stop point instead.
*/
if (stop_requested && xlogreader->ReadRecPtr > summary_start_lsn)
{
summary_end_lsn = xlogreader->ReadRecPtr;
break;
}
/* Feed block references from xlog record to block reference table. */
for (block_id = 0; block_id <= XLogRecMaxBlockId(xlogreader);
block_id++)
{
RelFileLocator rlocator;
ForkNumber forknum;
BlockNumber blocknum;
if (!XLogRecGetBlockTagExtended(xlogreader, block_id, &rlocator,
&forknum, &blocknum, NULL))
continue;
/*
* As we do elsewhere, ignore the FSM fork, because it's not fully
* WAL-logged.
*/
if (forknum != FSM_FORKNUM)
BlockRefTableMarkBlockModified(brtab, &rlocator, forknum,
blocknum);
}
/* Update our notion of where this summary file ends. */
summary_end_lsn = xlogreader->EndRecPtr;
/* Also update shared memory. */
LWLockAcquire(WALSummarizerLock, LW_EXCLUSIVE);
Assert(summary_end_lsn >= WalSummarizerCtl->pending_lsn);
Assert(summary_end_lsn >= WalSummarizerCtl->summarized_lsn);
WalSummarizerCtl->pending_lsn = summary_end_lsn;
LWLockRelease(WALSummarizerLock);
/*
* If we have a switch LSN and have reached it, stop before reading
* the next record.
*/
if (!XLogRecPtrIsInvalid(switch_lsn) &&
xlogreader->EndRecPtr >= switch_lsn)
break;
}
/* Destroy xlogreader. */
pfree(xlogreader->private_data);
XLogReaderFree(xlogreader);
/*
* If a timeline switch occurs, we may fail to make any progress at all
* before exiting the loop above. If that happens, we don't write a WAL
* summary file at all.
*/
if (summary_end_lsn > summary_start_lsn)
{
/* Generate temporary and final path name. */
snprintf(temp_path, MAXPGPATH,
XLOGDIR "/summaries/temp.summary");
snprintf(final_path, MAXPGPATH,
XLOGDIR "/summaries/%08X%08X%08X%08X%08X.summary",
tli,
LSN_FORMAT_ARGS(summary_start_lsn),
LSN_FORMAT_ARGS(summary_end_lsn));
/* Open the temporary file for writing. */
io.filepos = 0;
io.file = PathNameOpenFile(temp_path, O_WRONLY | O_CREAT | O_TRUNC);
if (io.file < 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not create file \"%s\": %m", temp_path)));
/* Write the data. */
WriteBlockRefTable(brtab, WriteWalSummary, &io);
/* Close temporary file and shut down xlogreader. */
FileClose(io.file);
/* Tell the user what we did. */
ereport(DEBUG1,
errmsg("summarized WAL on TLI %u from %X/%X to %X/%X",
tli,
LSN_FORMAT_ARGS(summary_start_lsn),
LSN_FORMAT_ARGS(summary_end_lsn)));
/* Durably rename the new summary into place. */
durable_rename(temp_path, final_path, ERROR);
}
return summary_end_lsn;
}
/*
* Special handling for WAL records with RM_DBASE_ID.
*/
static void
SummarizeDbaseRecord(XLogReaderState *xlogreader, BlockRefTable *brtab)
{
uint8 info = XLogRecGetInfo(xlogreader) & ~XLR_INFO_MASK;
/*
* We use relfilenode zero for a given database OID and tablespace OID to
* indicate that all relations with that pair of IDs have been recreated
* if they exist at all. Effectively, we're setting a limit block of 0 for
* all such relfilenodes.
*
* Technically, this special handling is only needed in the case of
* XLOG_DBASE_CREATE_FILE_COPY, because that can create a whole bunch of
* relation files in a directory without logging anything specific to each
* one. If we didn't mark the whole DB OID/TS OID combination in some way,
* then a tablespace that was dropped after the reference backup and
* recreated using the FILE_COPY method prior to the incremental backup
* would look just like one that was never touched at all, which would be
* catastrophic.
*
* But it seems best to adopt this treatment for all records that drop or
* create a DB OID/TS OID combination. That's similar to how we treat the
* limit block for individual relations, and it's an extra layer of safety
* here. We can never lose data by marking more stuff as needing to be
* backed up in full.
*/
if (info == XLOG_DBASE_CREATE_FILE_COPY)
{
xl_dbase_create_file_copy_rec *xlrec;
RelFileLocator rlocator;
xlrec =
(xl_dbase_create_file_copy_rec *) XLogRecGetData(xlogreader);
rlocator.spcOid = xlrec->tablespace_id;
rlocator.dbOid = xlrec->db_id;
rlocator.relNumber = 0;
BlockRefTableSetLimitBlock(brtab, &rlocator, MAIN_FORKNUM, 0);
}
else if (info == XLOG_DBASE_CREATE_WAL_LOG)
{
xl_dbase_create_wal_log_rec *xlrec;
RelFileLocator rlocator;
xlrec = (xl_dbase_create_wal_log_rec *) XLogRecGetData(xlogreader);
rlocator.spcOid = xlrec->tablespace_id;
rlocator.dbOid = xlrec->db_id;
rlocator.relNumber = 0;
BlockRefTableSetLimitBlock(brtab, &rlocator, MAIN_FORKNUM, 0);
}
else if (info == XLOG_DBASE_DROP)
{
xl_dbase_drop_rec *xlrec;
RelFileLocator rlocator;
int i;
xlrec = (xl_dbase_drop_rec *) XLogRecGetData(xlogreader);
rlocator.dbOid = xlrec->db_id;
rlocator.relNumber = 0;
for (i = 0; i < xlrec->ntablespaces; ++i)
{
rlocator.spcOid = xlrec->tablespace_ids[i];
BlockRefTableSetLimitBlock(brtab, &rlocator, MAIN_FORKNUM, 0);
}
}
}
/*
* Special handling for WAL records with RM_SMGR_ID.
*/
static void
SummarizeSmgrRecord(XLogReaderState *xlogreader, BlockRefTable *brtab)
{
uint8 info = XLogRecGetInfo(xlogreader) & ~XLR_INFO_MASK;
if (info == XLOG_SMGR_CREATE)
{
xl_smgr_create *xlrec;
/*
* If a new relation fork is created on disk, there is no point
* tracking anything about which blocks have been modified, because
* the whole thing will be new. Hence, set the limit block for this
* fork to 0.
*
* Ignore the FSM fork, which is not fully WAL-logged.
*/
xlrec = (xl_smgr_create *) XLogRecGetData(xlogreader);
if (xlrec->forkNum != FSM_FORKNUM)
BlockRefTableSetLimitBlock(brtab, &xlrec->rlocator,
xlrec->forkNum, 0);
}
else if (info == XLOG_SMGR_TRUNCATE)
{
xl_smgr_truncate *xlrec;
xlrec = (xl_smgr_truncate *) XLogRecGetData(xlogreader);
/*
* If a relation fork is truncated on disk, there is no point in
* tracking anything about block modifications beyond the truncation
* point.
*
* We ignore SMGR_TRUNCATE_FSM here because the FSM isn't fully
* WAL-logged and thus we can't track modified blocks for it anyway.
*/
if ((xlrec->flags & SMGR_TRUNCATE_HEAP) != 0)
BlockRefTableSetLimitBlock(brtab, &xlrec->rlocator,
MAIN_FORKNUM, xlrec->blkno);
if ((xlrec->flags & SMGR_TRUNCATE_VM) != 0)
BlockRefTableSetLimitBlock(brtab, &xlrec->rlocator,
VISIBILITYMAP_FORKNUM, xlrec->blkno);
}
}
/*
* Special handling for WAL records with RM_XACT_ID.
*/
static void
SummarizeXactRecord(XLogReaderState *xlogreader, BlockRefTable *brtab)
{
uint8 info = XLogRecGetInfo(xlogreader) & ~XLR_INFO_MASK;
uint8 xact_info = info & XLOG_XACT_OPMASK;
if (xact_info == XLOG_XACT_COMMIT ||
xact_info == XLOG_XACT_COMMIT_PREPARED)
{
xl_xact_commit *xlrec = (xl_xact_commit *) XLogRecGetData(xlogreader);
xl_xact_parsed_commit parsed;
int i;
/*
* Don't track modified blocks for any relations that were removed on
* commit.
*/
ParseCommitRecord(XLogRecGetInfo(xlogreader), xlrec, &parsed);
for (i = 0; i < parsed.nrels; ++i)
{
ForkNumber forknum;
for (forknum = 0; forknum <= MAX_FORKNUM; ++forknum)
if (forknum != FSM_FORKNUM)
BlockRefTableSetLimitBlock(brtab, &parsed.xlocators[i],
forknum, 0);
}
}
else if (xact_info == XLOG_XACT_ABORT ||
xact_info == XLOG_XACT_ABORT_PREPARED)
{
xl_xact_abort *xlrec = (xl_xact_abort *) XLogRecGetData(xlogreader);
xl_xact_parsed_abort parsed;
int i;
/*
* Don't track modified blocks for any relations that were removed on
* abort.
*/
ParseAbortRecord(XLogRecGetInfo(xlogreader), xlrec, &parsed);
for (i = 0; i < parsed.nrels; ++i)
{
ForkNumber forknum;
for (forknum = 0; forknum <= MAX_FORKNUM; ++forknum)
if (forknum != FSM_FORKNUM)
BlockRefTableSetLimitBlock(brtab, &parsed.xlocators[i],
forknum, 0);
}
}
}
/*
* Special handling for WAL records with RM_XLOG_ID.
*/
static bool
SummarizeXlogRecord(XLogReaderState *xlogreader)
{
uint8 info = XLogRecGetInfo(xlogreader) & ~XLR_INFO_MASK;
if (info == XLOG_CHECKPOINT_REDO || info == XLOG_CHECKPOINT_SHUTDOWN)
{
/*
* This is an LSN at which redo might begin, so we'd like
* summarization to stop just before this WAL record.
*/
return true;
}
return false;
}
/*
* Similar to read_local_xlog_page, but limited to read from one particular
* timeline. If the end of WAL is reached, it will wait for more if reading
* from the current timeline, or give up if reading from a historic timeline.
* In the latter case, it will also set private_data->end_of_wal = true.
*
* Caller must set private_data->tli to the TLI of interest,
* private_data->read_upto to the lowest LSN that is not known to be safe
* to read on that timeline, and private_data->historic to true if and only
* if the timeline is not the current timeline. This function will update
* private_data->read_upto and private_data->historic if more WAL appears
* on the current timeline or if the current timeline becomes historic.
*/
static int
summarizer_read_local_xlog_page(XLogReaderState *state,
XLogRecPtr targetPagePtr, int reqLen,
XLogRecPtr targetRecPtr, char *cur_page)
{
int count;
WALReadError errinfo;
SummarizerReadLocalXLogPrivate *private_data;
HandleWalSummarizerInterrupts();
private_data = (SummarizerReadLocalXLogPrivate *)
state->private_data;
while (1)
{
if (targetPagePtr + XLOG_BLCKSZ <= private_data->read_upto)
{
/*
* more than one block available; read only that block, have
* caller come back if they need more.
*/
count = XLOG_BLCKSZ;
break;
}
else if (targetPagePtr + reqLen > private_data->read_upto)
{
/* We don't seem to have enough data. */
if (private_data->historic)
{
/*
* This is a historic timeline, so there will never be any
* more data than we have currently.
*/
private_data->end_of_wal = true;
return -1;
}
else
{
XLogRecPtr latest_lsn;
TimeLineID latest_tli;
/*
* This is - or at least was up until very recently - the
* current timeline, so more data might show up. Delay here
* so we don't tight-loop.
*/
HandleWalSummarizerInterrupts();
summarizer_wait_for_wal();
/* Recheck end-of-WAL. */
latest_lsn = GetLatestLSN(&latest_tli);
if (private_data->tli == latest_tli)
{
/* Still the current timeline, update max LSN. */
Assert(latest_lsn >= private_data->read_upto);
private_data->read_upto = latest_lsn;
}
else
{
List *tles = readTimeLineHistory(latest_tli);
XLogRecPtr switchpoint;
/*
* The timeline we're scanning is no longer the latest
* one. Figure out when it ended.
*/
private_data->historic = true;
switchpoint = tliSwitchPoint(private_data->tli, tles,
NULL);
/*
* Allow reads up to exactly the switch point.
*
* It's possible that this will cause read_upto to move
* backwards, because walreceiver might have read a
* partial record and flushed it to disk, and we'd view
* that data as safe to read. However, the
* XLOG_END_OF_RECOVERY record will be written at the end
* of the last complete WAL record, not at the end of the
* WAL that we've flushed to disk.
*
* So switchpoint < private->read_upto is possible here,
* but switchpoint < state->EndRecPtr should not be.
*/
Assert(switchpoint >= state->EndRecPtr);
private_data->read_upto = switchpoint;
/* Debugging output. */
ereport(DEBUG1,
errmsg("timeline %u became historic, can read up to %X/%X",
private_data->tli, LSN_FORMAT_ARGS(private_data->read_upto)));
}
/* Go around and try again. */
}
}
else
{
/* enough bytes available to satisfy the request */
count = private_data->read_upto - targetPagePtr;
break;
}
}
if (!WALRead(state, cur_page, targetPagePtr, count,
private_data->tli, &errinfo))
WALReadRaiseError(&errinfo);
/* Track that we read a page, for sleep time calculation. */
++pages_read_since_last_sleep;
/* number of valid bytes in the buffer */
return count;
}
/*
* Sleep for long enough that we believe it's likely that more WAL will
* be available afterwards.
*/
static void
summarizer_wait_for_wal(void)
{
if (pages_read_since_last_sleep == 0)
{
/*
* No pages were read since the last sleep, so double the sleep time,
* but not beyond the maximum allowable value.
*/
sleep_quanta = Min(sleep_quanta * 2, MAX_SLEEP_QUANTA);
}
else if (pages_read_since_last_sleep > 1)
{
/*
* Multiple pages were read since the last sleep, so reduce the sleep
* time.
*
* A large burst of activity should be able to quickly reduce the
* sleep time to the minimum, but we don't want a handful of extra WAL
* records to provoke a strong reaction. We choose to reduce the sleep
* time by 1 quantum for each page read beyond the first, which is a
* fairly arbitrary way of trying to be reactive without overreacting.
*/
if (pages_read_since_last_sleep > sleep_quanta - 1)
sleep_quanta = 1;
else
sleep_quanta -= pages_read_since_last_sleep;
}
/* OK, now sleep. */
(void) WaitLatch(MyLatch,
WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
sleep_quanta * MS_PER_SLEEP_QUANTUM,
WAIT_EVENT_WAL_SUMMARIZER_WAL);
ResetLatch(MyLatch);
/* Reset count of pages read. */
pages_read_since_last_sleep = 0;
}
/*
* Remove WAL summaries whose mtimes are older than wal_summary_keep_time.
*/
static void
MaybeRemoveOldWalSummaries(void)
{
XLogRecPtr redo_pointer = GetRedoRecPtr();
List *wslist;
time_t cutoff_time;
/* If WAL summary removal is disabled, don't do anything. */
if (wal_summary_keep_time == 0)
return;
/*
* If the redo pointer has not advanced, don't do anything.
*
* This has the effect that we only try to remove old WAL summary files
* once per checkpoint cycle.
*/
if (redo_pointer == redo_pointer_at_last_summary_removal)
return;
redo_pointer_at_last_summary_removal = redo_pointer;
/*
* Files should only be removed if the last modification time precedes the
* cutoff time we compute here.
*/
cutoff_time = time(NULL) - 60 * wal_summary_keep_time;
/* Get all the summaries that currently exist. */
wslist = GetWalSummaries(0, InvalidXLogRecPtr, InvalidXLogRecPtr);
/* Loop until all summaries have been considered for removal. */
while (wslist != NIL)
{
ListCell *lc;
XLogSegNo oldest_segno;
XLogRecPtr oldest_lsn = InvalidXLogRecPtr;
TimeLineID selected_tli;
HandleWalSummarizerInterrupts();
/*
* Pick a timeline for which some summary files still exist on disk,
* and find the oldest LSN that still exists on disk for that
* timeline.
*/
selected_tli = ((WalSummaryFile *) linitial(wslist))->tli;
oldest_segno = XLogGetOldestSegno(selected_tli);
if (oldest_segno != 0)
XLogSegNoOffsetToRecPtr(oldest_segno, 0, wal_segment_size,
oldest_lsn);
/* Consider each WAL file on the selected timeline in turn. */
foreach(lc, wslist)
{
WalSummaryFile *ws = lfirst(lc);
HandleWalSummarizerInterrupts();
/* If it's not on this timeline, it's not time to consider it. */
if (selected_tli != ws->tli)
continue;
/*
* If the WAL doesn't exist any more, we can remove it if the file
* modification time is old enough.
*/
if (XLogRecPtrIsInvalid(oldest_lsn) || ws->end_lsn <= oldest_lsn)
RemoveWalSummaryIfOlderThan(ws, cutoff_time);
/*
* Whether we removed the file or not, we need not consider it
* again.
*/
wslist = foreach_delete_current(wslist, lc);
pfree(ws);
}
}
}
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