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checkpointer.c
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1 /*-------------------------------------------------------------------------
2  *
3  * checkpointer.c
4  *
5  * The checkpointer is new as of Postgres 9.2. It handles all checkpoints.
6  * Checkpoints are automatically dispatched after a certain amount of time has
7  * elapsed since the last one, and it can be signaled to perform requested
8  * checkpoints as well. (The GUC parameter that mandates a checkpoint every
9  * so many WAL segments is implemented by having backends signal when they
10  * fill WAL segments; the checkpointer itself doesn't watch for the
11  * condition.)
12  *
13  * Normal termination is by SIGUSR2, which instructs the checkpointer to
14  * execute a shutdown checkpoint and then exit(0). (All backends must be
15  * stopped before SIGUSR2 is issued!) Emergency termination is by SIGQUIT;
16  * like any backend, the checkpointer will simply abort and exit on SIGQUIT.
17  *
18  * If the checkpointer exits unexpectedly, the postmaster treats that the same
19  * as a backend crash: shared memory may be corrupted, so remaining backends
20  * should be killed by SIGQUIT and then a recovery cycle started. (Even if
21  * shared memory isn't corrupted, we have lost information about which
22  * files need to be fsync'd for the next checkpoint, and so a system
23  * restart needs to be forced.)
24  *
25  *
26  * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
27  *
28  *
29  * IDENTIFICATION
30  * src/backend/postmaster/checkpointer.c
31  *
32  *-------------------------------------------------------------------------
33  */
34 #include "postgres.h"
35 
36 #include <sys/time.h>
37 #include <time.h>
38 
39 #include "access/xlog.h"
40 #include "access/xlog_internal.h"
41 #include "access/xlogrecovery.h"
42 #include "libpq/pqsignal.h"
43 #include "miscadmin.h"
44 #include "pgstat.h"
45 #include "postmaster/bgwriter.h"
46 #include "postmaster/interrupt.h"
47 #include "replication/syncrep.h"
48 #include "storage/bufmgr.h"
50 #include "storage/fd.h"
51 #include "storage/ipc.h"
52 #include "storage/lwlock.h"
53 #include "storage/proc.h"
54 #include "storage/procsignal.h"
55 #include "storage/shmem.h"
56 #include "storage/smgr.h"
57 #include "storage/spin.h"
58 #include "utils/guc.h"
59 #include "utils/memutils.h"
60 #include "utils/resowner.h"
61 
62 
63 /*----------
64  * Shared memory area for communication between checkpointer and backends
65  *
66  * The ckpt counters allow backends to watch for completion of a checkpoint
67  * request they send. Here's how it works:
68  * * At start of a checkpoint, checkpointer reads (and clears) the request
69  * flags and increments ckpt_started, while holding ckpt_lck.
70  * * On completion of a checkpoint, checkpointer sets ckpt_done to
71  * equal ckpt_started.
72  * * On failure of a checkpoint, checkpointer increments ckpt_failed
73  * and sets ckpt_done to equal ckpt_started.
74  *
75  * The algorithm for backends is:
76  * 1. Record current values of ckpt_failed and ckpt_started, and
77  * set request flags, while holding ckpt_lck.
78  * 2. Send signal to request checkpoint.
79  * 3. Sleep until ckpt_started changes. Now you know a checkpoint has
80  * begun since you started this algorithm (although *not* that it was
81  * specifically initiated by your signal), and that it is using your flags.
82  * 4. Record new value of ckpt_started.
83  * 5. Sleep until ckpt_done >= saved value of ckpt_started. (Use modulo
84  * arithmetic here in case counters wrap around.) Now you know a
85  * checkpoint has started and completed, but not whether it was
86  * successful.
87  * 6. If ckpt_failed is different from the originally saved value,
88  * assume request failed; otherwise it was definitely successful.
89  *
90  * ckpt_flags holds the OR of the checkpoint request flags sent by all
91  * requesting backends since the last checkpoint start. The flags are
92  * chosen so that OR'ing is the correct way to combine multiple requests.
93  *
94  * num_backend_writes is used to count the number of buffer writes performed
95  * by user backend processes. This counter should be wide enough that it
96  * can't overflow during a single processing cycle. num_backend_fsync
97  * counts the subset of those writes that also had to do their own fsync,
98  * because the checkpointer failed to absorb their request.
99  *
100  * The requests array holds fsync requests sent by backends and not yet
101  * absorbed by the checkpointer.
102  *
103  * Unlike the checkpoint fields, num_backend_writes, num_backend_fsync, and
104  * the requests fields are protected by CheckpointerCommLock.
105  *----------
106  */
107 typedef struct
108 {
109  SyncRequestType type; /* request type */
110  FileTag ftag; /* file identifier */
112 
113 typedef struct
114 {
115  pid_t checkpointer_pid; /* PID (0 if not started) */
116 
117  slock_t ckpt_lck; /* protects all the ckpt_* fields */
118 
119  int ckpt_started; /* advances when checkpoint starts */
120  int ckpt_done; /* advances when checkpoint done */
121  int ckpt_failed; /* advances when checkpoint fails */
122 
123  int ckpt_flags; /* checkpoint flags, as defined in xlog.h */
124 
125  ConditionVariable start_cv; /* signaled when ckpt_started advances */
126  ConditionVariable done_cv; /* signaled when ckpt_done advances */
127 
128  uint32 num_backend_writes; /* counts user backend buffer writes */
129  uint32 num_backend_fsync; /* counts user backend fsync calls */
130 
131  int num_requests; /* current # of requests */
132  int max_requests; /* allocated array size */
135 
137 
138 /* interval for calling AbsorbSyncRequests in CheckpointWriteDelay */
139 #define WRITES_PER_ABSORB 1000
140 
141 /*
142  * GUC parameters
143  */
147 
148 /*
149  * Private state
150  */
151 static bool ckpt_active = false;
152 
153 /* these values are valid when ckpt_active is true: */
156 static double ckpt_cached_elapsed;
157 
160 
161 /* Prototypes for private functions */
162 
163 static void HandleCheckpointerInterrupts(void);
164 static void CheckArchiveTimeout(void);
165 static bool IsCheckpointOnSchedule(double progress);
166 static bool ImmediateCheckpointRequested(void);
167 static bool CompactCheckpointerRequestQueue(void);
168 static void UpdateSharedMemoryConfig(void);
169 
170 /* Signal handlers */
171 static void ReqCheckpointHandler(SIGNAL_ARGS);
172 
173 
174 /*
175  * Main entry point for checkpointer process
176  *
177  * This is invoked from AuxiliaryProcessMain, which has already created the
178  * basic execution environment, but not enabled signals yet.
179  */
180 void
182 {
183  sigjmp_buf local_sigjmp_buf;
184  MemoryContext checkpointer_context;
185 
187 
188  /*
189  * Properly accept or ignore signals the postmaster might send us
190  *
191  * Note: we deliberately ignore SIGTERM, because during a standard Unix
192  * system shutdown cycle, init will SIGTERM all processes at once. We
193  * want to wait for the backends to exit, whereupon the postmaster will
194  * tell us it's okay to shut down (via SIGUSR2).
195  */
197  pqsignal(SIGINT, ReqCheckpointHandler); /* request checkpoint */
198  pqsignal(SIGTERM, SIG_IGN); /* ignore SIGTERM */
199  /* SIGQUIT handler was already set up by InitPostmasterChild */
204 
205  /*
206  * Reset some signals that are accepted by postmaster but not here
207  */
209 
210  /*
211  * Initialize so that first time-driven event happens at the correct time.
212  */
214 
215  /*
216  * Write out stats after shutdown. This needs to be called by exactly one
217  * process during a normal shutdown, and since checkpointer is shut down
218  * very late...
219  *
220  * Walsenders are shut down after the checkpointer, but currently don't
221  * report stats. If that changes, we need a more complicated solution.
222  */
224 
225  /*
226  * Create a memory context that we will do all our work in. We do this so
227  * that we can reset the context during error recovery and thereby avoid
228  * possible memory leaks. Formerly this code just ran in
229  * TopMemoryContext, but resetting that would be a really bad idea.
230  */
231  checkpointer_context = AllocSetContextCreate(TopMemoryContext,
232  "Checkpointer",
234  MemoryContextSwitchTo(checkpointer_context);
235 
236  /*
237  * If an exception is encountered, processing resumes here.
238  *
239  * You might wonder why this isn't coded as an infinite loop around a
240  * PG_TRY construct. The reason is that this is the bottom of the
241  * exception stack, and so with PG_TRY there would be no exception handler
242  * in force at all during the CATCH part. By leaving the outermost setjmp
243  * always active, we have at least some chance of recovering from an error
244  * during error recovery. (If we get into an infinite loop thereby, it
245  * will soon be stopped by overflow of elog.c's internal state stack.)
246  *
247  * Note that we use sigsetjmp(..., 1), so that the prevailing signal mask
248  * (to wit, BlockSig) will be restored when longjmp'ing to here. Thus,
249  * signals other than SIGQUIT will be blocked until we complete error
250  * recovery. It might seem that this policy makes the HOLD_INTERRUPTS()
251  * call redundant, but it is not since InterruptPending might be set
252  * already.
253  */
254  if (sigsetjmp(local_sigjmp_buf, 1) != 0)
255  {
256  /* Since not using PG_TRY, must reset error stack by hand */
257  error_context_stack = NULL;
258 
259  /* Prevent interrupts while cleaning up */
260  HOLD_INTERRUPTS();
261 
262  /* Report the error to the server log */
263  EmitErrorReport();
264 
265  /*
266  * These operations are really just a minimal subset of
267  * AbortTransaction(). We don't have very many resources to worry
268  * about in checkpointer, but we do have LWLocks, buffers, and temp
269  * files.
270  */
274  AbortBufferIO();
275  UnlockBuffers();
277  AtEOXact_Buffers(false);
278  AtEOXact_SMgr();
279  AtEOXact_Files(false);
280  AtEOXact_HashTables(false);
281 
282  /* Warn any waiting backends that the checkpoint failed. */
283  if (ckpt_active)
284  {
289 
291 
292  ckpt_active = false;
293  }
294 
295  /*
296  * Now return to normal top-level context and clear ErrorContext for
297  * next time.
298  */
299  MemoryContextSwitchTo(checkpointer_context);
300  FlushErrorState();
301 
302  /* Flush any leaked data in the top-level context */
303  MemoryContextResetAndDeleteChildren(checkpointer_context);
304 
305  /* Now we can allow interrupts again */
307 
308  /*
309  * Sleep at least 1 second after any error. A write error is likely
310  * to be repeated, and we don't want to be filling the error logs as
311  * fast as we can.
312  */
313  pg_usleep(1000000L);
314 
315  /*
316  * Close all open files after any error. This is helpful on Windows,
317  * where holding deleted files open causes various strange errors.
318  * It's not clear we need it elsewhere, but shouldn't hurt.
319  */
320  smgrcloseall();
321  }
322 
323  /* We can now handle ereport(ERROR) */
324  PG_exception_stack = &local_sigjmp_buf;
325 
326  /*
327  * Unblock signals (they were blocked when the postmaster forked us)
328  */
330 
331  /*
332  * Ensure all shared memory values are set correctly for the config. Doing
333  * this here ensures no race conditions from other concurrent updaters.
334  */
336 
337  /*
338  * Advertise our latch that backends can use to wake us up while we're
339  * sleeping.
340  */
342 
343  /*
344  * Loop forever
345  */
346  for (;;)
347  {
348  bool do_checkpoint = false;
349  int flags = 0;
350  pg_time_t now;
351  int elapsed_secs;
352  int cur_timeout;
353 
354  /* Clear any already-pending wakeups */
356 
357  /*
358  * Process any requests or signals received recently.
359  */
362 
363  /*
364  * Detect a pending checkpoint request by checking whether the flags
365  * word in shared memory is nonzero. We shouldn't need to acquire the
366  * ckpt_lck for this.
367  */
368  if (((volatile CheckpointerShmemStruct *) CheckpointerShmem)->ckpt_flags)
369  {
370  do_checkpoint = true;
372  }
373 
374  /*
375  * Force a checkpoint if too much time has elapsed since the last one.
376  * Note that we count a timed checkpoint in stats only when this
377  * occurs without an external request, but we set the CAUSE_TIME flag
378  * bit even if there is also an external request.
379  */
380  now = (pg_time_t) time(NULL);
381  elapsed_secs = now - last_checkpoint_time;
382  if (elapsed_secs >= CheckPointTimeout)
383  {
384  if (!do_checkpoint)
386  do_checkpoint = true;
387  flags |= CHECKPOINT_CAUSE_TIME;
388  }
389 
390  /*
391  * Do a checkpoint if requested.
392  */
393  if (do_checkpoint)
394  {
395  bool ckpt_performed = false;
396  bool do_restartpoint;
397 
398  /* Check if we should perform a checkpoint or a restartpoint. */
399  do_restartpoint = RecoveryInProgress();
400 
401  /*
402  * Atomically fetch the request flags to figure out what kind of a
403  * checkpoint we should perform, and increase the started-counter
404  * to acknowledge that we've started a new checkpoint.
405  */
407  flags |= CheckpointerShmem->ckpt_flags;
411 
413 
414  /*
415  * The end-of-recovery checkpoint is a real checkpoint that's
416  * performed while we're still in recovery.
417  */
418  if (flags & CHECKPOINT_END_OF_RECOVERY)
419  do_restartpoint = false;
420 
421  /*
422  * We will warn if (a) too soon since last checkpoint (whatever
423  * caused it) and (b) somebody set the CHECKPOINT_CAUSE_XLOG flag
424  * since the last checkpoint start. Note in particular that this
425  * implementation will not generate warnings caused by
426  * CheckPointTimeout < CheckPointWarning.
427  */
428  if (!do_restartpoint &&
429  (flags & CHECKPOINT_CAUSE_XLOG) &&
430  elapsed_secs < CheckPointWarning)
431  ereport(LOG,
432  (errmsg_plural("checkpoints are occurring too frequently (%d second apart)",
433  "checkpoints are occurring too frequently (%d seconds apart)",
434  elapsed_secs,
435  elapsed_secs),
436  errhint("Consider increasing the configuration parameter \"max_wal_size\".")));
437 
438  /*
439  * Initialize checkpointer-private variables used during
440  * checkpoint.
441  */
442  ckpt_active = true;
443  if (do_restartpoint)
445  else
449 
450  /*
451  * Do the checkpoint.
452  */
453  if (!do_restartpoint)
454  {
455  CreateCheckPoint(flags);
456  ckpt_performed = true;
457  }
458  else
459  ckpt_performed = CreateRestartPoint(flags);
460 
461  /*
462  * After any checkpoint, close all smgr files. This is so we
463  * won't hang onto smgr references to deleted files indefinitely.
464  */
465  smgrcloseall();
466 
467  /*
468  * Indicate checkpoint completion to any waiting backends.
469  */
473 
475 
476  if (ckpt_performed)
477  {
478  /*
479  * Note we record the checkpoint start time not end time as
480  * last_checkpoint_time. This is so that time-driven
481  * checkpoints happen at a predictable spacing.
482  */
484  }
485  else
486  {
487  /*
488  * We were not able to perform the restartpoint (checkpoints
489  * throw an ERROR in case of error). Most likely because we
490  * have not received any new checkpoint WAL records since the
491  * last restartpoint. Try again in 15 s.
492  */
494  }
495 
496  ckpt_active = false;
497 
498  /* We may have received an interrupt during the checkpoint. */
500  }
501 
502  /* Check for archive_timeout and switch xlog files if necessary. */
504 
505  /* Report pending statistics to the cumulative stats system */
507  pgstat_report_wal(true);
508 
509  /*
510  * If any checkpoint flags have been set, redo the loop to handle the
511  * checkpoint without sleeping.
512  */
513  if (((volatile CheckpointerShmemStruct *) CheckpointerShmem)->ckpt_flags)
514  continue;
515 
516  /*
517  * Sleep until we are signaled or it's time for another checkpoint or
518  * xlog file switch.
519  */
520  now = (pg_time_t) time(NULL);
521  elapsed_secs = now - last_checkpoint_time;
522  if (elapsed_secs >= CheckPointTimeout)
523  continue; /* no sleep for us ... */
524  cur_timeout = CheckPointTimeout - elapsed_secs;
526  {
527  elapsed_secs = now - last_xlog_switch_time;
528  if (elapsed_secs >= XLogArchiveTimeout)
529  continue; /* no sleep for us ... */
530  cur_timeout = Min(cur_timeout, XLogArchiveTimeout - elapsed_secs);
531  }
532 
533  (void) WaitLatch(MyLatch,
535  cur_timeout * 1000L /* convert to ms */ ,
537  }
538 }
539 
540 /*
541  * Process any new interrupts.
542  */
543 static void
545 {
548 
550  {
551  ConfigReloadPending = false;
553 
554  /*
555  * Checkpointer is the last process to shut down, so we ask it to hold
556  * the keys for a range of other tasks required most of which have
557  * nothing to do with checkpointing at all.
558  *
559  * For various reasons, some config values can change dynamically so
560  * the primary copy of them is held in shared memory to make sure all
561  * backends see the same value. We make Checkpointer responsible for
562  * updating the shared memory copy if the parameter setting changes
563  * because of SIGHUP.
564  */
566  }
568  {
569  /*
570  * From here on, elog(ERROR) should end with exit(1), not send control
571  * back to the sigsetjmp block above
572  */
573  ExitOnAnyError = true;
574 
575  /*
576  * Close down the database.
577  *
578  * Since ShutdownXLOG() creates restartpoint or checkpoint, and
579  * updates the statistics, increment the checkpoint request and flush
580  * out pending statistic.
581  */
583  ShutdownXLOG(0, 0);
585  pgstat_report_wal(true);
586 
587  /* Normal exit from the checkpointer is here */
588  proc_exit(0); /* done */
589  }
590 
591  /* Perform logging of memory contexts of this process */
594 }
595 
596 /*
597  * CheckArchiveTimeout -- check for archive_timeout and switch xlog files
598  *
599  * This will switch to a new WAL file and force an archive file write if
600  * meaningful activity is recorded in the current WAL file. This includes most
601  * writes, including just a single checkpoint record, but excludes WAL records
602  * that were inserted with the XLOG_MARK_UNIMPORTANT flag being set (like
603  * snapshots of running transactions). Such records, depending on
604  * configuration, occur on regular intervals and don't contain important
605  * information. This avoids generating archives with a few unimportant
606  * records.
607  */
608 static void
610 {
611  pg_time_t now;
612  pg_time_t last_time;
613  XLogRecPtr last_switch_lsn;
614 
616  return;
617 
618  now = (pg_time_t) time(NULL);
619 
620  /* First we do a quick check using possibly-stale local state. */
622  return;
623 
624  /*
625  * Update local state ... note that last_xlog_switch_time is the last time
626  * a switch was performed *or requested*.
627  */
628  last_time = GetLastSegSwitchData(&last_switch_lsn);
629 
631 
632  /* Now we can do the real checks */
634  {
635  /*
636  * Switch segment only when "important" WAL has been logged since the
637  * last segment switch (last_switch_lsn points to end of segment
638  * switch occurred in).
639  */
640  if (GetLastImportantRecPtr() > last_switch_lsn)
641  {
642  XLogRecPtr switchpoint;
643 
644  /* mark switch as unimportant, avoids triggering checkpoints */
645  switchpoint = RequestXLogSwitch(true);
646 
647  /*
648  * If the returned pointer points exactly to a segment boundary,
649  * assume nothing happened.
650  */
651  if (XLogSegmentOffset(switchpoint, wal_segment_size) != 0)
652  elog(DEBUG1, "write-ahead log switch forced (archive_timeout=%d)",
654  }
655 
656  /*
657  * Update state in any case, so we don't retry constantly when the
658  * system is idle.
659  */
661  }
662 }
663 
664 /*
665  * Returns true if an immediate checkpoint request is pending. (Note that
666  * this does not check the *current* checkpoint's IMMEDIATE flag, but whether
667  * there is one pending behind it.)
668  */
669 static bool
671 {
673 
674  /*
675  * We don't need to acquire the ckpt_lck in this case because we're only
676  * looking at a single flag bit.
677  */
678  if (cps->ckpt_flags & CHECKPOINT_IMMEDIATE)
679  return true;
680  return false;
681 }
682 
683 /*
684  * CheckpointWriteDelay -- control rate of checkpoint
685  *
686  * This function is called after each page write performed by BufferSync().
687  * It is responsible for throttling BufferSync()'s write rate to hit
688  * checkpoint_completion_target.
689  *
690  * The checkpoint request flags should be passed in; currently the only one
691  * examined is CHECKPOINT_IMMEDIATE, which disables delays between writes.
692  *
693  * 'progress' is an estimate of how much of the work has been done, as a
694  * fraction between 0.0 meaning none, and 1.0 meaning all done.
695  */
696 void
697 CheckpointWriteDelay(int flags, double progress)
698 {
699  static int absorb_counter = WRITES_PER_ABSORB;
700 
701  /* Do nothing if checkpoint is being executed by non-checkpointer process */
702  if (!AmCheckpointerProcess())
703  return;
704 
705  /*
706  * Perform the usual duties and take a nap, unless we're behind schedule,
707  * in which case we just try to catch up as quickly as possible.
708  */
709  if (!(flags & CHECKPOINT_IMMEDIATE) &&
713  {
715  {
716  ConfigReloadPending = false;
718  /* update shmem copies of config variables */
720  }
721 
723  absorb_counter = WRITES_PER_ABSORB;
724 
726 
727  /* Report interim statistics to the cumulative stats system */
729 
730  /*
731  * This sleep used to be connected to bgwriter_delay, typically 200ms.
732  * That resulted in more frequent wakeups if not much work to do.
733  * Checkpointer and bgwriter are no longer related so take the Big
734  * Sleep.
735  */
737  100,
740  }
741  else if (--absorb_counter <= 0)
742  {
743  /*
744  * Absorb pending fsync requests after each WRITES_PER_ABSORB write
745  * operations even when we don't sleep, to prevent overflow of the
746  * fsync request queue.
747  */
749  absorb_counter = WRITES_PER_ABSORB;
750  }
751 
752  /* Check for barrier events. */
755 }
756 
757 /*
758  * IsCheckpointOnSchedule -- are we on schedule to finish this checkpoint
759  * (or restartpoint) in time?
760  *
761  * Compares the current progress against the time/segments elapsed since last
762  * checkpoint, and returns true if the progress we've made this far is greater
763  * than the elapsed time/segments.
764  */
765 static bool
767 {
768  XLogRecPtr recptr;
769  struct timeval now;
770  double elapsed_xlogs,
771  elapsed_time;
772 
774 
775  /* Scale progress according to checkpoint_completion_target. */
777 
778  /*
779  * Check against the cached value first. Only do the more expensive
780  * calculations once we reach the target previously calculated. Since
781  * neither time or WAL insert pointer moves backwards, a freshly
782  * calculated value can only be greater than or equal to the cached value.
783  */
785  return false;
786 
787  /*
788  * Check progress against WAL segments written and CheckPointSegments.
789  *
790  * We compare the current WAL insert location against the location
791  * computed before calling CreateCheckPoint. The code in XLogInsert that
792  * actually triggers a checkpoint when CheckPointSegments is exceeded
793  * compares against RedoRecPtr, so this is not completely accurate.
794  * However, it's good enough for our purposes, we're only calculating an
795  * estimate anyway.
796  *
797  * During recovery, we compare last replayed WAL record's location with
798  * the location computed before calling CreateRestartPoint. That maintains
799  * the same pacing as we have during checkpoints in normal operation, but
800  * we might exceed max_wal_size by a fair amount. That's because there can
801  * be a large gap between a checkpoint's redo-pointer and the checkpoint
802  * record itself, and we only start the restartpoint after we've seen the
803  * checkpoint record. (The gap is typically up to CheckPointSegments *
804  * checkpoint_completion_target where checkpoint_completion_target is the
805  * value that was in effect when the WAL was generated).
806  */
807  if (RecoveryInProgress())
808  recptr = GetXLogReplayRecPtr(NULL);
809  else
810  recptr = GetInsertRecPtr();
811  elapsed_xlogs = (((double) (recptr - ckpt_start_recptr)) /
813 
814  if (progress < elapsed_xlogs)
815  {
816  ckpt_cached_elapsed = elapsed_xlogs;
817  return false;
818  }
819 
820  /*
821  * Check progress against time elapsed and checkpoint_timeout.
822  */
823  gettimeofday(&now, NULL);
824  elapsed_time = ((double) ((pg_time_t) now.tv_sec - ckpt_start_time) +
825  now.tv_usec / 1000000.0) / CheckPointTimeout;
826 
827  if (progress < elapsed_time)
828  {
830  return false;
831  }
832 
833  /* It looks like we're on schedule. */
834  return true;
835 }
836 
837 
838 /* --------------------------------
839  * signal handler routines
840  * --------------------------------
841  */
842 
843 /* SIGINT: set flag to run a normal checkpoint right away */
844 static void
846 {
847  int save_errno = errno;
848 
849  /*
850  * The signaling process should have set ckpt_flags nonzero, so all we
851  * need do is ensure that our main loop gets kicked out of any wait.
852  */
853  SetLatch(MyLatch);
854 
855  errno = save_errno;
856 }
857 
858 
859 /* --------------------------------
860  * communication with backends
861  * --------------------------------
862  */
863 
864 /*
865  * CheckpointerShmemSize
866  * Compute space needed for checkpointer-related shared memory
867  */
868 Size
870 {
871  Size size;
872 
873  /*
874  * Currently, the size of the requests[] array is arbitrarily set equal to
875  * NBuffers. This may prove too large or small ...
876  */
877  size = offsetof(CheckpointerShmemStruct, requests);
878  size = add_size(size, mul_size(NBuffers, sizeof(CheckpointerRequest)));
879 
880  return size;
881 }
882 
883 /*
884  * CheckpointerShmemInit
885  * Allocate and initialize checkpointer-related shared memory
886  */
887 void
889 {
890  Size size = CheckpointerShmemSize();
891  bool found;
892 
894  ShmemInitStruct("Checkpointer Data",
895  size,
896  &found);
897 
898  if (!found)
899  {
900  /*
901  * First time through, so initialize. Note that we zero the whole
902  * requests array; this is so that CompactCheckpointerRequestQueue can
903  * assume that any pad bytes in the request structs are zeroes.
904  */
905  MemSet(CheckpointerShmem, 0, size);
910  }
911 }
912 
913 /*
914  * RequestCheckpoint
915  * Called in backend processes to request a checkpoint
916  *
917  * flags is a bitwise OR of the following:
918  * CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown.
919  * CHECKPOINT_END_OF_RECOVERY: checkpoint is for end of WAL recovery.
920  * CHECKPOINT_IMMEDIATE: finish the checkpoint ASAP,
921  * ignoring checkpoint_completion_target parameter.
922  * CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occurred
923  * since the last one (implied by CHECKPOINT_IS_SHUTDOWN or
924  * CHECKPOINT_END_OF_RECOVERY).
925  * CHECKPOINT_WAIT: wait for completion before returning (otherwise,
926  * just signal checkpointer to do it, and return).
927  * CHECKPOINT_CAUSE_XLOG: checkpoint is requested due to xlog filling.
928  * (This affects logging, and in particular enables CheckPointWarning.)
929  */
930 void
932 {
933  int ntries;
934  int old_failed,
935  old_started;
936 
937  /*
938  * If in a standalone backend, just do it ourselves.
939  */
941  {
942  /*
943  * There's no point in doing slow checkpoints in a standalone backend,
944  * because there's no other backends the checkpoint could disrupt.
945  */
947 
948  /*
949  * After any checkpoint, close all smgr files. This is so we won't
950  * hang onto smgr references to deleted files indefinitely.
951  */
952  smgrcloseall();
953 
954  return;
955  }
956 
957  /*
958  * Atomically set the request flags, and take a snapshot of the counters.
959  * When we see ckpt_started > old_started, we know the flags we set here
960  * have been seen by checkpointer.
961  *
962  * Note that we OR the flags with any existing flags, to avoid overriding
963  * a "stronger" request by another backend. The flag senses must be
964  * chosen to make this work!
965  */
967 
968  old_failed = CheckpointerShmem->ckpt_failed;
969  old_started = CheckpointerShmem->ckpt_started;
971 
973 
974  /*
975  * Send signal to request checkpoint. It's possible that the checkpointer
976  * hasn't started yet, or is in process of restarting, so we will retry a
977  * few times if needed. (Actually, more than a few times, since on slow
978  * or overloaded buildfarm machines, it's been observed that the
979  * checkpointer can take several seconds to start.) However, if not told
980  * to wait for the checkpoint to occur, we consider failure to send the
981  * signal to be nonfatal and merely LOG it. The checkpointer should see
982  * the request when it does start, with or without getting a signal.
983  */
984 #define MAX_SIGNAL_TRIES 600 /* max wait 60.0 sec */
985  for (ntries = 0;; ntries++)
986  {
988  {
989  if (ntries >= MAX_SIGNAL_TRIES || !(flags & CHECKPOINT_WAIT))
990  {
991  elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
992  "could not signal for checkpoint: checkpointer is not running");
993  break;
994  }
995  }
996  else if (kill(CheckpointerShmem->checkpointer_pid, SIGINT) != 0)
997  {
998  if (ntries >= MAX_SIGNAL_TRIES || !(flags & CHECKPOINT_WAIT))
999  {
1000  elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
1001  "could not signal for checkpoint: %m");
1002  break;
1003  }
1004  }
1005  else
1006  break; /* signal sent successfully */
1007 
1009  pg_usleep(100000L); /* wait 0.1 sec, then retry */
1010  }
1011 
1012  /*
1013  * If requested, wait for completion. We detect completion according to
1014  * the algorithm given above.
1015  */
1016  if (flags & CHECKPOINT_WAIT)
1017  {
1018  int new_started,
1019  new_failed;
1020 
1021  /* Wait for a new checkpoint to start. */
1023  for (;;)
1024  {
1026  new_started = CheckpointerShmem->ckpt_started;
1028 
1029  if (new_started != old_started)
1030  break;
1031 
1034  }
1036 
1037  /*
1038  * We are waiting for ckpt_done >= new_started, in a modulo sense.
1039  */
1041  for (;;)
1042  {
1043  int new_done;
1044 
1046  new_done = CheckpointerShmem->ckpt_done;
1047  new_failed = CheckpointerShmem->ckpt_failed;
1049 
1050  if (new_done - new_started >= 0)
1051  break;
1052 
1055  }
1057 
1058  if (new_failed != old_failed)
1059  ereport(ERROR,
1060  (errmsg("checkpoint request failed"),
1061  errhint("Consult recent messages in the server log for details.")));
1062  }
1063 }
1064 
1065 /*
1066  * ForwardSyncRequest
1067  * Forward a file-fsync request from a backend to the checkpointer
1068  *
1069  * Whenever a backend is compelled to write directly to a relation
1070  * (which should be seldom, if the background writer is getting its job done),
1071  * the backend calls this routine to pass over knowledge that the relation
1072  * is dirty and must be fsync'd before next checkpoint. We also use this
1073  * opportunity to count such writes for statistical purposes.
1074  *
1075  * To avoid holding the lock for longer than necessary, we normally write
1076  * to the requests[] queue without checking for duplicates. The checkpointer
1077  * will have to eliminate dups internally anyway. However, if we discover
1078  * that the queue is full, we make a pass over the entire queue to compact
1079  * it. This is somewhat expensive, but the alternative is for the backend
1080  * to perform its own fsync, which is far more expensive in practice. It
1081  * is theoretically possible a backend fsync might still be necessary, if
1082  * the queue is full and contains no duplicate entries. In that case, we
1083  * let the backend know by returning false.
1084  */
1085 bool
1087 {
1088  CheckpointerRequest *request;
1089  bool too_full;
1090 
1091  if (!IsUnderPostmaster)
1092  return false; /* probably shouldn't even get here */
1093 
1094  if (AmCheckpointerProcess())
1095  elog(ERROR, "ForwardSyncRequest must not be called in checkpointer");
1096 
1097  LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
1098 
1099  /* Count all backend writes regardless of if they fit in the queue */
1102 
1103  /*
1104  * If the checkpointer isn't running or the request queue is full, the
1105  * backend will have to perform its own fsync request. But before forcing
1106  * that to happen, we can try to compact the request queue.
1107  */
1108  if (CheckpointerShmem->checkpointer_pid == 0 ||
1111  {
1112  /*
1113  * Count the subset of writes where backends have to do their own
1114  * fsync
1115  */
1118  LWLockRelease(CheckpointerCommLock);
1119  return false;
1120  }
1121 
1122  /* OK, insert request */
1124  request->ftag = *ftag;
1125  request->type = type;
1126 
1127  /* If queue is more than half full, nudge the checkpointer to empty it */
1128  too_full = (CheckpointerShmem->num_requests >=
1130 
1131  LWLockRelease(CheckpointerCommLock);
1132 
1133  /* ... but not till after we release the lock */
1134  if (too_full && ProcGlobal->checkpointerLatch)
1136 
1137  return true;
1138 }
1139 
1140 /*
1141  * CompactCheckpointerRequestQueue
1142  * Remove duplicates from the request queue to avoid backend fsyncs.
1143  * Returns "true" if any entries were removed.
1144  *
1145  * Although a full fsync request queue is not common, it can lead to severe
1146  * performance problems when it does happen. So far, this situation has
1147  * only been observed to occur when the system is under heavy write load,
1148  * and especially during the "sync" phase of a checkpoint. Without this
1149  * logic, each backend begins doing an fsync for every block written, which
1150  * gets very expensive and can slow down the whole system.
1151  *
1152  * Trying to do this every time the queue is full could lose if there
1153  * aren't any removable entries. But that should be vanishingly rare in
1154  * practice: there's one queue entry per shared buffer.
1155  */
1156 static bool
1158 {
1159  struct CheckpointerSlotMapping
1160  {
1161  CheckpointerRequest request;
1162  int slot;
1163  };
1164 
1165  int n,
1166  preserve_count;
1167  int num_skipped = 0;
1168  HASHCTL ctl;
1169  HTAB *htab;
1170  bool *skip_slot;
1171 
1172  /* must hold CheckpointerCommLock in exclusive mode */
1173  Assert(LWLockHeldByMe(CheckpointerCommLock));
1174 
1175  /* Initialize skip_slot array */
1176  skip_slot = palloc0(sizeof(bool) * CheckpointerShmem->num_requests);
1177 
1178  /* Initialize temporary hash table */
1179  ctl.keysize = sizeof(CheckpointerRequest);
1180  ctl.entrysize = sizeof(struct CheckpointerSlotMapping);
1181  ctl.hcxt = CurrentMemoryContext;
1182 
1183  htab = hash_create("CompactCheckpointerRequestQueue",
1185  &ctl,
1187 
1188  /*
1189  * The basic idea here is that a request can be skipped if it's followed
1190  * by a later, identical request. It might seem more sensible to work
1191  * backwards from the end of the queue and check whether a request is
1192  * *preceded* by an earlier, identical request, in the hopes of doing less
1193  * copying. But that might change the semantics, if there's an
1194  * intervening SYNC_FORGET_REQUEST or SYNC_FILTER_REQUEST, so we do it
1195  * this way. It would be possible to be even smarter if we made the code
1196  * below understand the specific semantics of such requests (it could blow
1197  * away preceding entries that would end up being canceled anyhow), but
1198  * it's not clear that the extra complexity would buy us anything.
1199  */
1200  for (n = 0; n < CheckpointerShmem->num_requests; n++)
1201  {
1202  CheckpointerRequest *request;
1203  struct CheckpointerSlotMapping *slotmap;
1204  bool found;
1205 
1206  /*
1207  * We use the request struct directly as a hashtable key. This
1208  * assumes that any padding bytes in the structs are consistently the
1209  * same, which should be okay because we zeroed them in
1210  * CheckpointerShmemInit. Note also that RelFileLocator had better
1211  * contain no pad bytes.
1212  */
1213  request = &CheckpointerShmem->requests[n];
1214  slotmap = hash_search(htab, request, HASH_ENTER, &found);
1215  if (found)
1216  {
1217  /* Duplicate, so mark the previous occurrence as skippable */
1218  skip_slot[slotmap->slot] = true;
1219  num_skipped++;
1220  }
1221  /* Remember slot containing latest occurrence of this request value */
1222  slotmap->slot = n;
1223  }
1224 
1225  /* Done with the hash table. */
1226  hash_destroy(htab);
1227 
1228  /* If no duplicates, we're out of luck. */
1229  if (!num_skipped)
1230  {
1231  pfree(skip_slot);
1232  return false;
1233  }
1234 
1235  /* We found some duplicates; remove them. */
1236  preserve_count = 0;
1237  for (n = 0; n < CheckpointerShmem->num_requests; n++)
1238  {
1239  if (skip_slot[n])
1240  continue;
1241  CheckpointerShmem->requests[preserve_count++] = CheckpointerShmem->requests[n];
1242  }
1243  ereport(DEBUG1,
1244  (errmsg_internal("compacted fsync request queue from %d entries to %d entries",
1245  CheckpointerShmem->num_requests, preserve_count)));
1246  CheckpointerShmem->num_requests = preserve_count;
1247 
1248  /* Cleanup. */
1249  pfree(skip_slot);
1250  return true;
1251 }
1252 
1253 /*
1254  * AbsorbSyncRequests
1255  * Retrieve queued sync requests and pass them to sync mechanism.
1256  *
1257  * This is exported because it must be called during CreateCheckPoint;
1258  * we have to be sure we have accepted all pending requests just before
1259  * we start fsync'ing. Since CreateCheckPoint sometimes runs in
1260  * non-checkpointer processes, do nothing if not checkpointer.
1261  */
1262 void
1264 {
1265  CheckpointerRequest *requests = NULL;
1266  CheckpointerRequest *request;
1267  int n;
1268 
1269  if (!AmCheckpointerProcess())
1270  return;
1271 
1272  LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
1273 
1274  /* Transfer stats counts into pending pgstats message */
1279 
1282 
1283  /*
1284  * We try to avoid holding the lock for a long time by copying the request
1285  * array, and processing the requests after releasing the lock.
1286  *
1287  * Once we have cleared the requests from shared memory, we have to PANIC
1288  * if we then fail to absorb them (eg, because our hashtable runs out of
1289  * memory). This is because the system cannot run safely if we are unable
1290  * to fsync what we have been told to fsync. Fortunately, the hashtable
1291  * is so small that the problem is quite unlikely to arise in practice.
1292  */
1294  if (n > 0)
1295  {
1296  requests = (CheckpointerRequest *) palloc(n * sizeof(CheckpointerRequest));
1297  memcpy(requests, CheckpointerShmem->requests, n * sizeof(CheckpointerRequest));
1298  }
1299 
1301 
1303 
1304  LWLockRelease(CheckpointerCommLock);
1305 
1306  for (request = requests; n > 0; request++, n--)
1307  RememberSyncRequest(&request->ftag, request->type);
1308 
1309  END_CRIT_SECTION();
1310 
1311  if (requests)
1312  pfree(requests);
1313 }
1314 
1315 /*
1316  * Update any shared memory configurations based on config parameters
1317  */
1318 static void
1320 {
1321  /* update global shmem state for sync rep */
1323 
1324  /*
1325  * If full_page_writes has been changed by SIGHUP, we update it in shared
1326  * memory and write an XLOG_FPW_CHANGE record.
1327  */
1329 
1330  elog(DEBUG2, "checkpointer updated shared memory configuration values");
1331 }
1332 
1333 /*
1334  * FirstCallSinceLastCheckpoint allows a process to take an action once
1335  * per checkpoint cycle by asynchronously checking for checkpoint completion.
1336  */
1337 bool
1339 {
1340  static int ckpt_done = 0;
1341  int new_done;
1342  bool FirstCall = false;
1343 
1345  new_done = CheckpointerShmem->ckpt_done;
1347 
1348  if (new_done != ckpt_done)
1349  FirstCall = true;
1350 
1351  ckpt_done = new_done;
1352 
1353  return FirstCall;
1354 }
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Definition: checkpointer.c:126
ConditionVariable start_cv
Definition: checkpointer.c:125
CheckpointerRequest requests[FLEXIBLE_ARRAY_MEMBER]
Definition: checkpointer.c:133
Definition: sync.h:51
Size keysize
Definition: hsearch.h:75
Size entrysize
Definition: hsearch.h:76
MemoryContext hcxt
Definition: hsearch.h:86
Definition: dynahash.c:220
Latch procLatch
Definition: proc.h:168
Latch * checkpointerLatch
Definition: proc.h:390
PgStat_Counter buf_written_backend
Definition: pgstat.h:275
PgStat_Counter requested_checkpoints
Definition: pgstat.h:271
PgStat_Counter timed_checkpoints
Definition: pgstat.h:270
PgStat_Counter buf_fsync_backend
Definition: pgstat.h:276
void RememberSyncRequest(const FileTag *ftag, SyncRequestType type)
Definition: sync.c:494
SyncRequestType
Definition: sync.h:24
void SyncRepUpdateSyncStandbysDefined(void)
Definition: syncrep.c:947
@ WAIT_EVENT_CHECKPOINTER_MAIN
Definition: wait_event.h:42
@ WAIT_EVENT_CHECKPOINT_START
Definition: wait_event.h:91
@ WAIT_EVENT_CHECKPOINT_DONE
Definition: wait_event.h:90
@ WAIT_EVENT_CHECKPOINT_WRITE_DELAY
Definition: wait_event.h:143
static void pgstat_report_wait_end(void)
Definition: wait_event.h:282
#define SIGCHLD
Definition: win32_port.h:177
#define SIGHUP
Definition: win32_port.h:167
#define SIG_DFL
Definition: win32_port.h:162
#define SIGPIPE
Definition: win32_port.h:172
#define kill(pid, sig)
Definition: win32_port.h:464
#define SIGUSR1
Definition: win32_port.h:179
#define SIGALRM
Definition: win32_port.h:173
#define SIGUSR2
Definition: win32_port.h:180
#define SIG_IGN
Definition: win32_port.h:164
void UpdateFullPageWrites(void)
Definition: xlog.c:7469
bool RecoveryInProgress(void)
Definition: xlog.c:5759
XLogRecPtr RequestXLogSwitch(bool mark_unimportant)
Definition: xlog.c:7363
bool CreateRestartPoint(int flags)
Definition: xlog.c:6917
XLogRecPtr GetInsertRecPtr(void)
Definition: xlog.c:5907
int wal_segment_size
Definition: xlog.c:144
void ShutdownXLOG(int code, Datum arg)
Definition: xlog.c:6010
int XLogArchiveTimeout
Definition: xlog.c:119
pg_time_t GetLastSegSwitchData(XLogRecPtr *lastSwitchLSN)
Definition: xlog.c:5993
XLogRecPtr GetLastImportantRecPtr(void)
Definition: xlog.c:5964
int CheckPointSegments
Definition: xlog.c:157
void CreateCheckPoint(int flags)
Definition: xlog.c:6276
#define CHECKPOINT_CAUSE_XLOG
Definition: xlog.h:143
#define CHECKPOINT_END_OF_RECOVERY
Definition: xlog.h:135
#define CHECKPOINT_CAUSE_TIME
Definition: xlog.h:144
#define CHECKPOINT_REQUESTED
Definition: xlog.h:141
#define CHECKPOINT_WAIT
Definition: xlog.h:140
#define CHECKPOINT_IMMEDIATE
Definition: xlog.h:136
#define XLogSegmentOffset(xlogptr, wal_segsz_bytes)
uint64 XLogRecPtr
Definition: xlogdefs.h:21
XLogRecPtr GetXLogReplayRecPtr(TimeLineID *replayTLI)