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 * The checkpointer is started by the postmaster as soon as the startup
14 * subprocess finishes, or as soon as recovery begins if we are doing archive
15 * recovery. It remains alive until the postmaster commands it to terminate.
16 * Normal termination is by SIGUSR2, which instructs the checkpointer to
17 * execute a shutdown checkpoint and then exit(0). (All backends must be
18 * stopped before SIGUSR2 is issued!) Emergency termination is by SIGQUIT;
19 * like any backend, the checkpointer will simply abort and exit on SIGQUIT.
20 *
21 * If the checkpointer exits unexpectedly, the postmaster treats that the same
22 * as a backend crash: shared memory may be corrupted, so remaining backends
23 * should be killed by SIGQUIT and then a recovery cycle started. (Even if
24 * shared memory isn't corrupted, we have lost information about which
25 * files need to be fsync'd for the next checkpoint, and so a system
26 * restart needs to be forced.)
27 *
28 *
29 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
30 *
31 *
32 * IDENTIFICATION
33 * src/backend/postmaster/checkpointer.c
34 *
35 *-------------------------------------------------------------------------
36 */
37 #include "postgres.h"
38
39 #include <sys/time.h>
40 #include <time.h>
41
42 #include "access/xlog.h"
43 #include "access/xlog_internal.h"
44 #include "libpq/pqsignal.h"
45 #include "miscadmin.h"
46 #include "pgstat.h"
47 #include "postmaster/bgwriter.h"
48 #include "postmaster/interrupt.h"
49 #include "replication/syncrep.h"
50 #include "storage/bufmgr.h"
51 #include "storage/condition_variable.h"
52 #include "storage/fd.h"
53 #include "storage/ipc.h"
54 #include "storage/lwlock.h"
55 #include "storage/proc.h"
56 #include "storage/procsignal.h"
57 #include "storage/shmem.h"
58 #include "storage/smgr.h"
59 #include "storage/spin.h"
60 #include "utils/guc.h"
61 #include "utils/memutils.h"
62 #include "utils/resowner.h"
63
64
65 /*----------
66 * Shared memory area for communication between checkpointer and backends
67 *
68 * The ckpt counters allow backends to watch for completion of a checkpoint
69 * request they send. Here's how it works:
70 * * At start of a checkpoint, checkpointer reads (and clears) the request
71 * flags and increments ckpt_started, while holding ckpt_lck.
72 * * On completion of a checkpoint, checkpointer sets ckpt_done to
73 * equal ckpt_started.
74 * * On failure of a checkpoint, checkpointer increments ckpt_failed
75 * and sets ckpt_done to equal ckpt_started.
76 *
77 * The algorithm for backends is:
78 * 1. Record current values of ckpt_failed and ckpt_started, and
79 * set request flags, while holding ckpt_lck.
80 * 2. Send signal to request checkpoint.
81 * 3. Sleep until ckpt_started changes. Now you know a checkpoint has
82 * begun since you started this algorithm (although *not* that it was
83 * specifically initiated by your signal), and that it is using your flags.
84 * 4. Record new value of ckpt_started.
85 * 5. Sleep until ckpt_done >= saved value of ckpt_started. (Use modulo
86 * arithmetic here in case counters wrap around.) Now you know a
87 * checkpoint has started and completed, but not whether it was
88 * successful.
89 * 6. If ckpt_failed is different from the originally saved value,
90 * assume request failed; otherwise it was definitely successful.
91 *
92 * ckpt_flags holds the OR of the checkpoint request flags sent by all
93 * requesting backends since the last checkpoint start. The flags are
94 * chosen so that OR'ing is the correct way to combine multiple requests.
95 *
96 * num_backend_writes is used to count the number of buffer writes performed
97 * by user backend processes. This counter should be wide enough that it
98 * can't overflow during a single processing cycle. num_backend_fsync
99 * counts the subset of those writes that also had to do their own fsync,
100 * because the checkpointer failed to absorb their request.
101 *
102 * The requests array holds fsync requests sent by backends and not yet
103 * absorbed by the checkpointer.
104 *
105 * Unlike the checkpoint fields, num_backend_writes, num_backend_fsync, and
106 * the requests fields are protected by CheckpointerCommLock.
107 *----------
108 */
109 typedef struct
110 {
111 SyncRequestType type; /* request type */
112 FileTag ftag; /* file identifier */
113 } CheckpointerRequest;
114
115 typedef struct
116 {
117 pid_t checkpointer_pid; /* PID (0 if not started) */
118
119 slock_t ckpt_lck; /* protects all the ckpt_* fields */
120
121 int ckpt_started; /* advances when checkpoint starts */
122 int ckpt_done; /* advances when checkpoint done */
123 int ckpt_failed; /* advances when checkpoint fails */
124
125 int ckpt_flags; /* checkpoint flags, as defined in xlog.h */
126
127 ConditionVariable start_cv; /* signaled when ckpt_started advances */
128 ConditionVariable done_cv; /* signaled when ckpt_done advances */
129
130 uint32 num_backend_writes; /* counts user backend buffer writes */
131 uint32 num_backend_fsync; /* counts user backend fsync calls */
132
133 int num_requests; /* current # of requests */
134 int max_requests; /* allocated array size */
135 CheckpointerRequest requests[FLEXIBLE_ARRAY_MEMBER];
136 } CheckpointerShmemStruct;
137
138 static CheckpointerShmemStruct *CheckpointerShmem;
139
140 /* interval for calling AbsorbSyncRequests in CheckpointWriteDelay */
141 #define WRITES_PER_ABSORB 1000
142
143 /*
144 * GUC parameters
145 */
146 int CheckPointTimeout = 300;
147 int CheckPointWarning = 30;
148 double CheckPointCompletionTarget = 0.9;
149
150 /*
151 * Private state
152 */
153 static bool ckpt_active = false;
154
155 /* these values are valid when ckpt_active is true: */
156 static pg_time_t ckpt_start_time;
157 static XLogRecPtr ckpt_start_recptr;
158 static double ckpt_cached_elapsed;
159
160 static pg_time_t last_checkpoint_time;
161 static pg_time_t last_xlog_switch_time;
162
163 /* Prototypes for private functions */
164
165 static void HandleCheckpointerInterrupts(void);
166 static void CheckArchiveTimeout(void);
167 static bool IsCheckpointOnSchedule(double progress);
168 static bool ImmediateCheckpointRequested(void);
169 static bool CompactCheckpointerRequestQueue(void);
170 static void UpdateSharedMemoryConfig(void);
171
172 /* Signal handlers */
173 static void ReqCheckpointHandler(SIGNAL_ARGS);
174
175
176 /*
177 * Main entry point for checkpointer process
178 *
179 * This is invoked from AuxiliaryProcessMain, which has already created the
180 * basic execution environment, but not enabled signals yet.
181 */
182 void
CheckpointerMain(void)183 CheckpointerMain(void)
184 {
185 sigjmp_buf local_sigjmp_buf;
186 MemoryContext checkpointer_context;
187
188 CheckpointerShmem->checkpointer_pid = MyProcPid;
189
190 /*
191 * Properly accept or ignore signals the postmaster might send us
192 *
193 * Note: we deliberately ignore SIGTERM, because during a standard Unix
194 * system shutdown cycle, init will SIGTERM all processes at once. We
195 * want to wait for the backends to exit, whereupon the postmaster will
196 * tell us it's okay to shut down (via SIGUSR2).
197 */
198 pqsignal(SIGHUP, SignalHandlerForConfigReload);
199 pqsignal(SIGINT, ReqCheckpointHandler); /* request checkpoint */
200 pqsignal(SIGTERM, SIG_IGN); /* ignore SIGTERM */
201 /* SIGQUIT handler was already set up by InitPostmasterChild */
202 pqsignal(SIGALRM, SIG_IGN);
203 pqsignal(SIGPIPE, SIG_IGN);
204 pqsignal(SIGUSR1, procsignal_sigusr1_handler);
205 pqsignal(SIGUSR2, SignalHandlerForShutdownRequest);
206
207 /*
208 * Reset some signals that are accepted by postmaster but not here
209 */
210 pqsignal(SIGCHLD, SIG_DFL);
211
212 /*
213 * Initialize so that first time-driven event happens at the correct time.
214 */
215 last_checkpoint_time = last_xlog_switch_time = (pg_time_t) time(NULL);
216
217 /*
218 * Create a memory context that we will do all our work in. We do this so
219 * that we can reset the context during error recovery and thereby avoid
220 * possible memory leaks. Formerly this code just ran in
221 * TopMemoryContext, but resetting that would be a really bad idea.
222 */
223 checkpointer_context = AllocSetContextCreate(TopMemoryContext,
224 "Checkpointer",
225 ALLOCSET_DEFAULT_SIZES);
226 MemoryContextSwitchTo(checkpointer_context);
227
228 /*
229 * If an exception is encountered, processing resumes here.
230 *
231 * You might wonder why this isn't coded as an infinite loop around a
232 * PG_TRY construct. The reason is that this is the bottom of the
233 * exception stack, and so with PG_TRY there would be no exception handler
234 * in force at all during the CATCH part. By leaving the outermost setjmp
235 * always active, we have at least some chance of recovering from an error
236 * during error recovery. (If we get into an infinite loop thereby, it
237 * will soon be stopped by overflow of elog.c's internal state stack.)
238 *
239 * Note that we use sigsetjmp(..., 1), so that the prevailing signal mask
240 * (to wit, BlockSig) will be restored when longjmp'ing to here. Thus,
241 * signals other than SIGQUIT will be blocked until we complete error
242 * recovery. It might seem that this policy makes the HOLD_INTERRUPTS()
243 * call redundant, but it is not since InterruptPending might be set
244 * already.
245 */
246 if (sigsetjmp(local_sigjmp_buf, 1) != 0)
247 {
248 /* Since not using PG_TRY, must reset error stack by hand */
249 error_context_stack = NULL;
250
251 /* Prevent interrupts while cleaning up */
252 HOLD_INTERRUPTS();
253
254 /* Report the error to the server log */
255 EmitErrorReport();
256
257 /*
258 * These operations are really just a minimal subset of
259 * AbortTransaction(). We don't have very many resources to worry
260 * about in checkpointer, but we do have LWLocks, buffers, and temp
261 * files.
262 */
263 LWLockReleaseAll();
264 ConditionVariableCancelSleep();
265 pgstat_report_wait_end();
266 AbortBufferIO();
267 UnlockBuffers();
268 ReleaseAuxProcessResources(false);
269 AtEOXact_Buffers(false);
270 AtEOXact_SMgr();
271 AtEOXact_Files(false);
272 AtEOXact_HashTables(false);
273
274 /* Warn any waiting backends that the checkpoint failed. */
275 if (ckpt_active)
276 {
277 SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
278 CheckpointerShmem->ckpt_failed++;
279 CheckpointerShmem->ckpt_done = CheckpointerShmem->ckpt_started;
280 SpinLockRelease(&CheckpointerShmem->ckpt_lck);
281
282 ConditionVariableBroadcast(&CheckpointerShmem->done_cv);
283
284 ckpt_active = false;
285 }
286
287 /*
288 * Now return to normal top-level context and clear ErrorContext for
289 * next time.
290 */
291 MemoryContextSwitchTo(checkpointer_context);
292 FlushErrorState();
293
294 /* Flush any leaked data in the top-level context */
295 MemoryContextResetAndDeleteChildren(checkpointer_context);
296
297 /* Now we can allow interrupts again */
298 RESUME_INTERRUPTS();
299
300 /*
301 * Sleep at least 1 second after any error. A write error is likely
302 * to be repeated, and we don't want to be filling the error logs as
303 * fast as we can.
304 */
305 pg_usleep(1000000L);
306
307 /*
308 * Close all open files after any error. This is helpful on Windows,
309 * where holding deleted files open causes various strange errors.
310 * It's not clear we need it elsewhere, but shouldn't hurt.
311 */
312 smgrcloseall();
313 }
314
315 /* We can now handle ereport(ERROR) */
316 PG_exception_stack = &local_sigjmp_buf;
317
318 /*
319 * Unblock signals (they were blocked when the postmaster forked us)
320 */
321 PG_SETMASK(&UnBlockSig);
322
323 /*
324 * Ensure all shared memory values are set correctly for the config. Doing
325 * this here ensures no race conditions from other concurrent updaters.
326 */
327 UpdateSharedMemoryConfig();
328
329 /*
330 * Advertise our latch that backends can use to wake us up while we're
331 * sleeping.
332 */
333 ProcGlobal->checkpointerLatch = &MyProc->procLatch;
334
335 /*
336 * Loop forever
337 */
338 for (;;)
339 {
340 bool do_checkpoint = false;
341 int flags = 0;
342 pg_time_t now;
343 int elapsed_secs;
344 int cur_timeout;
345
346 /* Clear any already-pending wakeups */
347 ResetLatch(MyLatch);
348
349 /*
350 * Process any requests or signals received recently.
351 */
352 AbsorbSyncRequests();
353 HandleCheckpointerInterrupts();
354
355 /*
356 * Detect a pending checkpoint request by checking whether the flags
357 * word in shared memory is nonzero. We shouldn't need to acquire the
358 * ckpt_lck for this.
359 */
360 if (((volatile CheckpointerShmemStruct *) CheckpointerShmem)->ckpt_flags)
361 {
362 do_checkpoint = true;
363 BgWriterStats.m_requested_checkpoints++;
364 }
365
366 /*
367 * Force a checkpoint if too much time has elapsed since the last one.
368 * Note that we count a timed checkpoint in stats only when this
369 * occurs without an external request, but we set the CAUSE_TIME flag
370 * bit even if there is also an external request.
371 */
372 now = (pg_time_t) time(NULL);
373 elapsed_secs = now - last_checkpoint_time;
374 if (elapsed_secs >= CheckPointTimeout)
375 {
376 if (!do_checkpoint)
377 BgWriterStats.m_timed_checkpoints++;
378 do_checkpoint = true;
379 flags |= CHECKPOINT_CAUSE_TIME;
380 }
381
382 /*
383 * Do a checkpoint if requested.
384 */
385 if (do_checkpoint)
386 {
387 bool ckpt_performed = false;
388 bool do_restartpoint;
389
390 /*
391 * Check if we should perform a checkpoint or a restartpoint. As a
392 * side-effect, RecoveryInProgress() initializes TimeLineID if
393 * it's not set yet.
394 */
395 do_restartpoint = RecoveryInProgress();
396
397 /*
398 * Atomically fetch the request flags to figure out what kind of a
399 * checkpoint we should perform, and increase the started-counter
400 * to acknowledge that we've started a new checkpoint.
401 */
402 SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
403 flags |= CheckpointerShmem->ckpt_flags;
404 CheckpointerShmem->ckpt_flags = 0;
405 CheckpointerShmem->ckpt_started++;
406 SpinLockRelease(&CheckpointerShmem->ckpt_lck);
407
408 ConditionVariableBroadcast(&CheckpointerShmem->start_cv);
409
410 /*
411 * The end-of-recovery checkpoint is a real checkpoint that's
412 * performed while we're still in recovery.
413 */
414 if (flags & CHECKPOINT_END_OF_RECOVERY)
415 do_restartpoint = false;
416
417 /*
418 * We will warn if (a) too soon since last checkpoint (whatever
419 * caused it) and (b) somebody set the CHECKPOINT_CAUSE_XLOG flag
420 * since the last checkpoint start. Note in particular that this
421 * implementation will not generate warnings caused by
422 * CheckPointTimeout < CheckPointWarning.
423 */
424 if (!do_restartpoint &&
425 (flags & CHECKPOINT_CAUSE_XLOG) &&
426 elapsed_secs < CheckPointWarning)
427 ereport(LOG,
428 (errmsg_plural("checkpoints are occurring too frequently (%d second apart)",
429 "checkpoints are occurring too frequently (%d seconds apart)",
430 elapsed_secs,
431 elapsed_secs),
432 errhint("Consider increasing the configuration parameter \"max_wal_size\".")));
433
434 /*
435 * Initialize checkpointer-private variables used during
436 * checkpoint.
437 */
438 ckpt_active = true;
439 if (do_restartpoint)
440 ckpt_start_recptr = GetXLogReplayRecPtr(NULL);
441 else
442 ckpt_start_recptr = GetInsertRecPtr();
443 ckpt_start_time = now;
444 ckpt_cached_elapsed = 0;
445
446 /*
447 * Do the checkpoint.
448 */
449 if (!do_restartpoint)
450 {
451 CreateCheckPoint(flags);
452 ckpt_performed = true;
453 }
454 else
455 ckpt_performed = CreateRestartPoint(flags);
456
457 /*
458 * After any checkpoint, close all smgr files. This is so we
459 * won't hang onto smgr references to deleted files indefinitely.
460 */
461 smgrcloseall();
462
463 /*
464 * Indicate checkpoint completion to any waiting backends.
465 */
466 SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
467 CheckpointerShmem->ckpt_done = CheckpointerShmem->ckpt_started;
468 SpinLockRelease(&CheckpointerShmem->ckpt_lck);
469
470 ConditionVariableBroadcast(&CheckpointerShmem->done_cv);
471
472 if (ckpt_performed)
473 {
474 /*
475 * Note we record the checkpoint start time not end time as
476 * last_checkpoint_time. This is so that time-driven
477 * checkpoints happen at a predictable spacing.
478 */
479 last_checkpoint_time = now;
480 }
481 else
482 {
483 /*
484 * We were not able to perform the restartpoint (checkpoints
485 * throw an ERROR in case of error). Most likely because we
486 * have not received any new checkpoint WAL records since the
487 * last restartpoint. Try again in 15 s.
488 */
489 last_checkpoint_time = now - CheckPointTimeout + 15;
490 }
491
492 ckpt_active = false;
493 }
494
495 /* Check for archive_timeout and switch xlog files if necessary. */
496 CheckArchiveTimeout();
497
498 /*
499 * Send off activity statistics to the stats collector. (The reason
500 * why we re-use bgwriter-related code for this is that the bgwriter
501 * and checkpointer used to be just one process. It's probably not
502 * worth the trouble to split the stats support into two independent
503 * stats message types.)
504 */
505 pgstat_send_bgwriter();
506
507 /* Send WAL statistics to the stats collector. */
508 pgstat_send_wal(true);
509
510 /*
511 * If any checkpoint flags have been set, redo the loop to handle the
512 * checkpoint without sleeping.
513 */
514 if (((volatile CheckpointerShmemStruct *) CheckpointerShmem)->ckpt_flags)
515 continue;
516
517 /*
518 * Sleep until we are signaled or it's time for another checkpoint or
519 * xlog file switch.
520 */
521 now = (pg_time_t) time(NULL);
522 elapsed_secs = now - last_checkpoint_time;
523 if (elapsed_secs >= CheckPointTimeout)
524 continue; /* no sleep for us ... */
525 cur_timeout = CheckPointTimeout - elapsed_secs;
526 if (XLogArchiveTimeout > 0 && !RecoveryInProgress())
527 {
528 elapsed_secs = now - last_xlog_switch_time;
529 if (elapsed_secs >= XLogArchiveTimeout)
530 continue; /* no sleep for us ... */
531 cur_timeout = Min(cur_timeout, XLogArchiveTimeout - elapsed_secs);
532 }
533
534 (void) WaitLatch(MyLatch,
535 WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
536 cur_timeout * 1000L /* convert to ms */ ,
537 WAIT_EVENT_CHECKPOINTER_MAIN);
538 }
539 }
540
541 /*
542 * Process any new interrupts.
543 */
544 static void
HandleCheckpointerInterrupts(void)545 HandleCheckpointerInterrupts(void)
546 {
547 if (ProcSignalBarrierPending)
548 ProcessProcSignalBarrier();
549
550 if (ConfigReloadPending)
551 {
552 ConfigReloadPending = false;
553 ProcessConfigFile(PGC_SIGHUP);
554
555 /*
556 * Checkpointer is the last process to shut down, so we ask it to hold
557 * the keys for a range of other tasks required most of which have
558 * nothing to do with checkpointing at all.
559 *
560 * For various reasons, some config values can change dynamically so
561 * the primary copy of them is held in shared memory to make sure all
562 * backends see the same value. We make Checkpointer responsible for
563 * updating the shared memory copy if the parameter setting changes
564 * because of SIGHUP.
565 */
566 UpdateSharedMemoryConfig();
567 }
568 if (ShutdownRequestPending)
569 {
570 /*
571 * From here on, elog(ERROR) should end with exit(1), not send control
572 * back to the sigsetjmp block above
573 */
574 ExitOnAnyError = true;
575
576 /*
577 * Close down the database.
578 *
579 * Since ShutdownXLOG() creates restartpoint or checkpoint, and
580 * updates the statistics, increment the checkpoint request and send
581 * the statistics to the stats collector.
582 */
583 BgWriterStats.m_requested_checkpoints++;
584 ShutdownXLOG(0, 0);
585 pgstat_send_bgwriter();
586 pgstat_send_wal(true);
587
588 /* Normal exit from the checkpointer is here */
589 proc_exit(0); /* done */
590 }
591 }
592
593 /*
594 * CheckArchiveTimeout -- check for archive_timeout and switch xlog files
595 *
596 * This will switch to a new WAL file and force an archive file write if
597 * meaningful activity is recorded in the current WAL file. This includes most
598 * writes, including just a single checkpoint record, but excludes WAL records
599 * that were inserted with the XLOG_MARK_UNIMPORTANT flag being set (like
600 * snapshots of running transactions). Such records, depending on
601 * configuration, occur on regular intervals and don't contain important
602 * information. This avoids generating archives with a few unimportant
603 * records.
604 */
605 static void
CheckArchiveTimeout(void)606 CheckArchiveTimeout(void)
607 {
608 pg_time_t now;
609 pg_time_t last_time;
610 XLogRecPtr last_switch_lsn;
611
612 if (XLogArchiveTimeout <= 0 || RecoveryInProgress())
613 return;
614
615 now = (pg_time_t) time(NULL);
616
617 /* First we do a quick check using possibly-stale local state. */
618 if ((int) (now - last_xlog_switch_time) < XLogArchiveTimeout)
619 return;
620
621 /*
622 * Update local state ... note that last_xlog_switch_time is the last time
623 * a switch was performed *or requested*.
624 */
625 last_time = GetLastSegSwitchData(&last_switch_lsn);
626
627 last_xlog_switch_time = Max(last_xlog_switch_time, last_time);
628
629 /* Now we can do the real checks */
630 if ((int) (now - last_xlog_switch_time) >= XLogArchiveTimeout)
631 {
632 /*
633 * Switch segment only when "important" WAL has been logged since the
634 * last segment switch (last_switch_lsn points to end of segment
635 * switch occurred in).
636 */
637 if (GetLastImportantRecPtr() > last_switch_lsn)
638 {
639 XLogRecPtr switchpoint;
640
641 /* mark switch as unimportant, avoids triggering checkpoints */
642 switchpoint = RequestXLogSwitch(true);
643
644 /*
645 * If the returned pointer points exactly to a segment boundary,
646 * assume nothing happened.
647 */
648 if (XLogSegmentOffset(switchpoint, wal_segment_size) != 0)
649 elog(DEBUG1, "write-ahead log switch forced (archive_timeout=%d)",
650 XLogArchiveTimeout);
651 }
652
653 /*
654 * Update state in any case, so we don't retry constantly when the
655 * system is idle.
656 */
657 last_xlog_switch_time = now;
658 }
659 }
660
661 /*
662 * Returns true if an immediate checkpoint request is pending. (Note that
663 * this does not check the *current* checkpoint's IMMEDIATE flag, but whether
664 * there is one pending behind it.)
665 */
666 static bool
ImmediateCheckpointRequested(void)667 ImmediateCheckpointRequested(void)
668 {
669 volatile CheckpointerShmemStruct *cps = CheckpointerShmem;
670
671 /*
672 * We don't need to acquire the ckpt_lck in this case because we're only
673 * looking at a single flag bit.
674 */
675 if (cps->ckpt_flags & CHECKPOINT_IMMEDIATE)
676 return true;
677 return false;
678 }
679
680 /*
681 * CheckpointWriteDelay -- control rate of checkpoint
682 *
683 * This function is called after each page write performed by BufferSync().
684 * It is responsible for throttling BufferSync()'s write rate to hit
685 * checkpoint_completion_target.
686 *
687 * The checkpoint request flags should be passed in; currently the only one
688 * examined is CHECKPOINT_IMMEDIATE, which disables delays between writes.
689 *
690 * 'progress' is an estimate of how much of the work has been done, as a
691 * fraction between 0.0 meaning none, and 1.0 meaning all done.
692 */
693 void
CheckpointWriteDelay(int flags,double progress)694 CheckpointWriteDelay(int flags, double progress)
695 {
696 static int absorb_counter = WRITES_PER_ABSORB;
697
698 /* Do nothing if checkpoint is being executed by non-checkpointer process */
699 if (!AmCheckpointerProcess())
700 return;
701
702 /*
703 * Perform the usual duties and take a nap, unless we're behind schedule,
704 * in which case we just try to catch up as quickly as possible.
705 */
706 if (!(flags & CHECKPOINT_IMMEDIATE) &&
707 !ShutdownRequestPending &&
708 !ImmediateCheckpointRequested() &&
709 IsCheckpointOnSchedule(progress))
710 {
711 if (ConfigReloadPending)
712 {
713 ConfigReloadPending = false;
714 ProcessConfigFile(PGC_SIGHUP);
715 /* update shmem copies of config variables */
716 UpdateSharedMemoryConfig();
717 }
718
719 AbsorbSyncRequests();
720 absorb_counter = WRITES_PER_ABSORB;
721
722 CheckArchiveTimeout();
723
724 /*
725 * Report interim activity statistics to the stats collector.
726 */
727 pgstat_send_bgwriter();
728
729 /*
730 * This sleep used to be connected to bgwriter_delay, typically 200ms.
731 * That resulted in more frequent wakeups if not much work to do.
732 * Checkpointer and bgwriter are no longer related so take the Big
733 * Sleep.
734 */
735 pg_usleep(100000L);
736 }
737 else if (--absorb_counter <= 0)
738 {
739 /*
740 * Absorb pending fsync requests after each WRITES_PER_ABSORB write
741 * operations even when we don't sleep, to prevent overflow of the
742 * fsync request queue.
743 */
744 AbsorbSyncRequests();
745 absorb_counter = WRITES_PER_ABSORB;
746 }
747
748 /* Check for barrier events. */
749 if (ProcSignalBarrierPending)
750 ProcessProcSignalBarrier();
751 }
752
753 /*
754 * IsCheckpointOnSchedule -- are we on schedule to finish this checkpoint
755 * (or restartpoint) in time?
756 *
757 * Compares the current progress against the time/segments elapsed since last
758 * checkpoint, and returns true if the progress we've made this far is greater
759 * than the elapsed time/segments.
760 */
761 static bool
IsCheckpointOnSchedule(double progress)762 IsCheckpointOnSchedule(double progress)
763 {
764 XLogRecPtr recptr;
765 struct timeval now;
766 double elapsed_xlogs,
767 elapsed_time;
768
769 Assert(ckpt_active);
770
771 /* Scale progress according to checkpoint_completion_target. */
772 progress *= CheckPointCompletionTarget;
773
774 /*
775 * Check against the cached value first. Only do the more expensive
776 * calculations once we reach the target previously calculated. Since
777 * neither time or WAL insert pointer moves backwards, a freshly
778 * calculated value can only be greater than or equal to the cached value.
779 */
780 if (progress < ckpt_cached_elapsed)
781 return false;
782
783 /*
784 * Check progress against WAL segments written and CheckPointSegments.
785 *
786 * We compare the current WAL insert location against the location
787 * computed before calling CreateCheckPoint. The code in XLogInsert that
788 * actually triggers a checkpoint when CheckPointSegments is exceeded
789 * compares against RedoRecPtr, so this is not completely accurate.
790 * However, it's good enough for our purposes, we're only calculating an
791 * estimate anyway.
792 *
793 * During recovery, we compare last replayed WAL record's location with
794 * the location computed before calling CreateRestartPoint. That maintains
795 * the same pacing as we have during checkpoints in normal operation, but
796 * we might exceed max_wal_size by a fair amount. That's because there can
797 * be a large gap between a checkpoint's redo-pointer and the checkpoint
798 * record itself, and we only start the restartpoint after we've seen the
799 * checkpoint record. (The gap is typically up to CheckPointSegments *
800 * checkpoint_completion_target where checkpoint_completion_target is the
801 * value that was in effect when the WAL was generated).
802 */
803 if (RecoveryInProgress())
804 recptr = GetXLogReplayRecPtr(NULL);
805 else
806 recptr = GetInsertRecPtr();
807 elapsed_xlogs = (((double) (recptr - ckpt_start_recptr)) /
808 wal_segment_size) / CheckPointSegments;
809
810 if (progress < elapsed_xlogs)
811 {
812 ckpt_cached_elapsed = elapsed_xlogs;
813 return false;
814 }
815
816 /*
817 * Check progress against time elapsed and checkpoint_timeout.
818 */
819 gettimeofday(&now, NULL);
820 elapsed_time = ((double) ((pg_time_t) now.tv_sec - ckpt_start_time) +
821 now.tv_usec / 1000000.0) / CheckPointTimeout;
822
823 if (progress < elapsed_time)
824 {
825 ckpt_cached_elapsed = elapsed_time;
826 return false;
827 }
828
829 /* It looks like we're on schedule. */
830 return true;
831 }
832
833
834 /* --------------------------------
835 * signal handler routines
836 * --------------------------------
837 */
838
839 /* SIGINT: set flag to run a normal checkpoint right away */
840 static void
ReqCheckpointHandler(SIGNAL_ARGS)841 ReqCheckpointHandler(SIGNAL_ARGS)
842 {
843 int save_errno = errno;
844
845 /*
846 * The signaling process should have set ckpt_flags nonzero, so all we
847 * need do is ensure that our main loop gets kicked out of any wait.
848 */
849 SetLatch(MyLatch);
850
851 errno = save_errno;
852 }
853
854
855 /* --------------------------------
856 * communication with backends
857 * --------------------------------
858 */
859
860 /*
861 * CheckpointerShmemSize
862 * Compute space needed for checkpointer-related shared memory
863 */
864 Size
CheckpointerShmemSize(void)865 CheckpointerShmemSize(void)
866 {
867 Size size;
868
869 /*
870 * Currently, the size of the requests[] array is arbitrarily set equal to
871 * NBuffers. This may prove too large or small ...
872 */
873 size = offsetof(CheckpointerShmemStruct, requests);
874 size = add_size(size, mul_size(NBuffers, sizeof(CheckpointerRequest)));
875
876 return size;
877 }
878
879 /*
880 * CheckpointerShmemInit
881 * Allocate and initialize checkpointer-related shared memory
882 */
883 void
CheckpointerShmemInit(void)884 CheckpointerShmemInit(void)
885 {
886 Size size = CheckpointerShmemSize();
887 bool found;
888
889 CheckpointerShmem = (CheckpointerShmemStruct *)
890 ShmemInitStruct("Checkpointer Data",
891 size,
892 &found);
893
894 if (!found)
895 {
896 /*
897 * First time through, so initialize. Note that we zero the whole
898 * requests array; this is so that CompactCheckpointerRequestQueue can
899 * assume that any pad bytes in the request structs are zeroes.
900 */
901 MemSet(CheckpointerShmem, 0, size);
902 SpinLockInit(&CheckpointerShmem->ckpt_lck);
903 CheckpointerShmem->max_requests = NBuffers;
904 ConditionVariableInit(&CheckpointerShmem->start_cv);
905 ConditionVariableInit(&CheckpointerShmem->done_cv);
906 }
907 }
908
909 /*
910 * RequestCheckpoint
911 * Called in backend processes to request a checkpoint
912 *
913 * flags is a bitwise OR of the following:
914 * CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown.
915 * CHECKPOINT_END_OF_RECOVERY: checkpoint is for end of WAL recovery.
916 * CHECKPOINT_IMMEDIATE: finish the checkpoint ASAP,
917 * ignoring checkpoint_completion_target parameter.
918 * CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occurred
919 * since the last one (implied by CHECKPOINT_IS_SHUTDOWN or
920 * CHECKPOINT_END_OF_RECOVERY).
921 * CHECKPOINT_WAIT: wait for completion before returning (otherwise,
922 * just signal checkpointer to do it, and return).
923 * CHECKPOINT_CAUSE_XLOG: checkpoint is requested due to xlog filling.
924 * (This affects logging, and in particular enables CheckPointWarning.)
925 */
926 void
RequestCheckpoint(int flags)927 RequestCheckpoint(int flags)
928 {
929 int ntries;
930 int old_failed,
931 old_started;
932
933 /*
934 * If in a standalone backend, just do it ourselves.
935 */
936 if (!IsPostmasterEnvironment)
937 {
938 /*
939 * There's no point in doing slow checkpoints in a standalone backend,
940 * because there's no other backends the checkpoint could disrupt.
941 */
942 CreateCheckPoint(flags | CHECKPOINT_IMMEDIATE);
943
944 /*
945 * After any checkpoint, close all smgr files. This is so we won't
946 * hang onto smgr references to deleted files indefinitely.
947 */
948 smgrcloseall();
949
950 return;
951 }
952
953 /*
954 * Atomically set the request flags, and take a snapshot of the counters.
955 * When we see ckpt_started > old_started, we know the flags we set here
956 * have been seen by checkpointer.
957 *
958 * Note that we OR the flags with any existing flags, to avoid overriding
959 * a "stronger" request by another backend. The flag senses must be
960 * chosen to make this work!
961 */
962 SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
963
964 old_failed = CheckpointerShmem->ckpt_failed;
965 old_started = CheckpointerShmem->ckpt_started;
966 CheckpointerShmem->ckpt_flags |= (flags | CHECKPOINT_REQUESTED);
967
968 SpinLockRelease(&CheckpointerShmem->ckpt_lck);
969
970 /*
971 * Send signal to request checkpoint. It's possible that the checkpointer
972 * hasn't started yet, or is in process of restarting, so we will retry a
973 * few times if needed. (Actually, more than a few times, since on slow
974 * or overloaded buildfarm machines, it's been observed that the
975 * checkpointer can take several seconds to start.) However, if not told
976 * to wait for the checkpoint to occur, we consider failure to send the
977 * signal to be nonfatal and merely LOG it. The checkpointer should see
978 * the request when it does start, with or without getting a signal.
979 */
980 #define MAX_SIGNAL_TRIES 600 /* max wait 60.0 sec */
981 for (ntries = 0;; ntries++)
982 {
983 if (CheckpointerShmem->checkpointer_pid == 0)
984 {
985 if (ntries >= MAX_SIGNAL_TRIES || !(flags & CHECKPOINT_WAIT))
986 {
987 elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
988 "could not signal for checkpoint: checkpointer is not running");
989 break;
990 }
991 }
992 else if (kill(CheckpointerShmem->checkpointer_pid, SIGINT) != 0)
993 {
994 if (ntries >= MAX_SIGNAL_TRIES || !(flags & CHECKPOINT_WAIT))
995 {
996 elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
997 "could not signal for checkpoint: %m");
998 break;
999 }
1000 }
1001 else
1002 break; /* signal sent successfully */
1003
1004 CHECK_FOR_INTERRUPTS();
1005 pg_usleep(100000L); /* wait 0.1 sec, then retry */
1006 }
1007
1008 /*
1009 * If requested, wait for completion. We detect completion according to
1010 * the algorithm given above.
1011 */
1012 if (flags & CHECKPOINT_WAIT)
1013 {
1014 int new_started,
1015 new_failed;
1016
1017 /* Wait for a new checkpoint to start. */
1018 ConditionVariablePrepareToSleep(&CheckpointerShmem->start_cv);
1019 for (;;)
1020 {
1021 SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
1022 new_started = CheckpointerShmem->ckpt_started;
1023 SpinLockRelease(&CheckpointerShmem->ckpt_lck);
1024
1025 if (new_started != old_started)
1026 break;
1027
1028 ConditionVariableSleep(&CheckpointerShmem->start_cv,
1029 WAIT_EVENT_CHECKPOINT_START);
1030 }
1031 ConditionVariableCancelSleep();
1032
1033 /*
1034 * We are waiting for ckpt_done >= new_started, in a modulo sense.
1035 */
1036 ConditionVariablePrepareToSleep(&CheckpointerShmem->done_cv);
1037 for (;;)
1038 {
1039 int new_done;
1040
1041 SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
1042 new_done = CheckpointerShmem->ckpt_done;
1043 new_failed = CheckpointerShmem->ckpt_failed;
1044 SpinLockRelease(&CheckpointerShmem->ckpt_lck);
1045
1046 if (new_done - new_started >= 0)
1047 break;
1048
1049 ConditionVariableSleep(&CheckpointerShmem->done_cv,
1050 WAIT_EVENT_CHECKPOINT_DONE);
1051 }
1052 ConditionVariableCancelSleep();
1053
1054 if (new_failed != old_failed)
1055 ereport(ERROR,
1056 (errmsg("checkpoint request failed"),
1057 errhint("Consult recent messages in the server log for details.")));
1058 }
1059 }
1060
1061 /*
1062 * ForwardSyncRequest
1063 * Forward a file-fsync request from a backend to the checkpointer
1064 *
1065 * Whenever a backend is compelled to write directly to a relation
1066 * (which should be seldom, if the background writer is getting its job done),
1067 * the backend calls this routine to pass over knowledge that the relation
1068 * is dirty and must be fsync'd before next checkpoint. We also use this
1069 * opportunity to count such writes for statistical purposes.
1070 *
1071 * To avoid holding the lock for longer than necessary, we normally write
1072 * to the requests[] queue without checking for duplicates. The checkpointer
1073 * will have to eliminate dups internally anyway. However, if we discover
1074 * that the queue is full, we make a pass over the entire queue to compact
1075 * it. This is somewhat expensive, but the alternative is for the backend
1076 * to perform its own fsync, which is far more expensive in practice. It
1077 * is theoretically possible a backend fsync might still be necessary, if
1078 * the queue is full and contains no duplicate entries. In that case, we
1079 * let the backend know by returning false.
1080 */
1081 bool
ForwardSyncRequest(const FileTag * ftag,SyncRequestType type)1082 ForwardSyncRequest(const FileTag *ftag, SyncRequestType type)
1083 {
1084 CheckpointerRequest *request;
1085 bool too_full;
1086
1087 if (!IsUnderPostmaster)
1088 return false; /* probably shouldn't even get here */
1089
1090 if (AmCheckpointerProcess())
1091 elog(ERROR, "ForwardSyncRequest must not be called in checkpointer");
1092
1093 LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
1094
1095 /* Count all backend writes regardless of if they fit in the queue */
1096 if (!AmBackgroundWriterProcess())
1097 CheckpointerShmem->num_backend_writes++;
1098
1099 /*
1100 * If the checkpointer isn't running or the request queue is full, the
1101 * backend will have to perform its own fsync request. But before forcing
1102 * that to happen, we can try to compact the request queue.
1103 */
1104 if (CheckpointerShmem->checkpointer_pid == 0 ||
1105 (CheckpointerShmem->num_requests >= CheckpointerShmem->max_requests &&
1106 !CompactCheckpointerRequestQueue()))
1107 {
1108 /*
1109 * Count the subset of writes where backends have to do their own
1110 * fsync
1111 */
1112 if (!AmBackgroundWriterProcess())
1113 CheckpointerShmem->num_backend_fsync++;
1114 LWLockRelease(CheckpointerCommLock);
1115 return false;
1116 }
1117
1118 /* OK, insert request */
1119 request = &CheckpointerShmem->requests[CheckpointerShmem->num_requests++];
1120 request->ftag = *ftag;
1121 request->type = type;
1122
1123 /* If queue is more than half full, nudge the checkpointer to empty it */
1124 too_full = (CheckpointerShmem->num_requests >=
1125 CheckpointerShmem->max_requests / 2);
1126
1127 LWLockRelease(CheckpointerCommLock);
1128
1129 /* ... but not till after we release the lock */
1130 if (too_full && ProcGlobal->checkpointerLatch)
1131 SetLatch(ProcGlobal->checkpointerLatch);
1132
1133 return true;
1134 }
1135
1136 /*
1137 * CompactCheckpointerRequestQueue
1138 * Remove duplicates from the request queue to avoid backend fsyncs.
1139 * Returns "true" if any entries were removed.
1140 *
1141 * Although a full fsync request queue is not common, it can lead to severe
1142 * performance problems when it does happen. So far, this situation has
1143 * only been observed to occur when the system is under heavy write load,
1144 * and especially during the "sync" phase of a checkpoint. Without this
1145 * logic, each backend begins doing an fsync for every block written, which
1146 * gets very expensive and can slow down the whole system.
1147 *
1148 * Trying to do this every time the queue is full could lose if there
1149 * aren't any removable entries. But that should be vanishingly rare in
1150 * practice: there's one queue entry per shared buffer.
1151 */
1152 static bool
CompactCheckpointerRequestQueue(void)1153 CompactCheckpointerRequestQueue(void)
1154 {
1155 struct CheckpointerSlotMapping
1156 {
1157 CheckpointerRequest request;
1158 int slot;
1159 };
1160
1161 int n,
1162 preserve_count;
1163 int num_skipped = 0;
1164 HASHCTL ctl;
1165 HTAB *htab;
1166 bool *skip_slot;
1167
1168 /* must hold CheckpointerCommLock in exclusive mode */
1169 Assert(LWLockHeldByMe(CheckpointerCommLock));
1170
1171 /* Initialize skip_slot array */
1172 skip_slot = palloc0(sizeof(bool) * CheckpointerShmem->num_requests);
1173
1174 /* Initialize temporary hash table */
1175 ctl.keysize = sizeof(CheckpointerRequest);
1176 ctl.entrysize = sizeof(struct CheckpointerSlotMapping);
1177 ctl.hcxt = CurrentMemoryContext;
1178
1179 htab = hash_create("CompactCheckpointerRequestQueue",
1180 CheckpointerShmem->num_requests,
1181 &ctl,
1182 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
1183
1184 /*
1185 * The basic idea here is that a request can be skipped if it's followed
1186 * by a later, identical request. It might seem more sensible to work
1187 * backwards from the end of the queue and check whether a request is
1188 * *preceded* by an earlier, identical request, in the hopes of doing less
1189 * copying. But that might change the semantics, if there's an
1190 * intervening SYNC_FORGET_REQUEST or SYNC_FILTER_REQUEST, so we do it
1191 * this way. It would be possible to be even smarter if we made the code
1192 * below understand the specific semantics of such requests (it could blow
1193 * away preceding entries that would end up being canceled anyhow), but
1194 * it's not clear that the extra complexity would buy us anything.
1195 */
1196 for (n = 0; n < CheckpointerShmem->num_requests; n++)
1197 {
1198 CheckpointerRequest *request;
1199 struct CheckpointerSlotMapping *slotmap;
1200 bool found;
1201
1202 /*
1203 * We use the request struct directly as a hashtable key. This
1204 * assumes that any padding bytes in the structs are consistently the
1205 * same, which should be okay because we zeroed them in
1206 * CheckpointerShmemInit. Note also that RelFileNode had better
1207 * contain no pad bytes.
1208 */
1209 request = &CheckpointerShmem->requests[n];
1210 slotmap = hash_search(htab, request, HASH_ENTER, &found);
1211 if (found)
1212 {
1213 /* Duplicate, so mark the previous occurrence as skippable */
1214 skip_slot[slotmap->slot] = true;
1215 num_skipped++;
1216 }
1217 /* Remember slot containing latest occurrence of this request value */
1218 slotmap->slot = n;
1219 }
1220
1221 /* Done with the hash table. */
1222 hash_destroy(htab);
1223
1224 /* If no duplicates, we're out of luck. */
1225 if (!num_skipped)
1226 {
1227 pfree(skip_slot);
1228 return false;
1229 }
1230
1231 /* We found some duplicates; remove them. */
1232 preserve_count = 0;
1233 for (n = 0; n < CheckpointerShmem->num_requests; n++)
1234 {
1235 if (skip_slot[n])
1236 continue;
1237 CheckpointerShmem->requests[preserve_count++] = CheckpointerShmem->requests[n];
1238 }
1239 ereport(DEBUG1,
1240 (errmsg_internal("compacted fsync request queue from %d entries to %d entries",
1241 CheckpointerShmem->num_requests, preserve_count)));
1242 CheckpointerShmem->num_requests = preserve_count;
1243
1244 /* Cleanup. */
1245 pfree(skip_slot);
1246 return true;
1247 }
1248
1249 /*
1250 * AbsorbSyncRequests
1251 * Retrieve queued sync requests and pass them to sync mechanism.
1252 *
1253 * This is exported because it must be called during CreateCheckPoint;
1254 * we have to be sure we have accepted all pending requests just before
1255 * we start fsync'ing. Since CreateCheckPoint sometimes runs in
1256 * non-checkpointer processes, do nothing if not checkpointer.
1257 */
1258 void
AbsorbSyncRequests(void)1259 AbsorbSyncRequests(void)
1260 {
1261 CheckpointerRequest *requests = NULL;
1262 CheckpointerRequest *request;
1263 int n;
1264
1265 if (!AmCheckpointerProcess())
1266 return;
1267
1268 LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
1269
1270 /* Transfer stats counts into pending pgstats message */
1271 BgWriterStats.m_buf_written_backend += CheckpointerShmem->num_backend_writes;
1272 BgWriterStats.m_buf_fsync_backend += CheckpointerShmem->num_backend_fsync;
1273
1274 CheckpointerShmem->num_backend_writes = 0;
1275 CheckpointerShmem->num_backend_fsync = 0;
1276
1277 /*
1278 * We try to avoid holding the lock for a long time by copying the request
1279 * array, and processing the requests after releasing the lock.
1280 *
1281 * Once we have cleared the requests from shared memory, we have to PANIC
1282 * if we then fail to absorb them (eg, because our hashtable runs out of
1283 * memory). This is because the system cannot run safely if we are unable
1284 * to fsync what we have been told to fsync. Fortunately, the hashtable
1285 * is so small that the problem is quite unlikely to arise in practice.
1286 */
1287 n = CheckpointerShmem->num_requests;
1288 if (n > 0)
1289 {
1290 requests = (CheckpointerRequest *) palloc(n * sizeof(CheckpointerRequest));
1291 memcpy(requests, CheckpointerShmem->requests, n * sizeof(CheckpointerRequest));
1292 }
1293
1294 START_CRIT_SECTION();
1295
1296 CheckpointerShmem->num_requests = 0;
1297
1298 LWLockRelease(CheckpointerCommLock);
1299
1300 for (request = requests; n > 0; request++, n--)
1301 RememberSyncRequest(&request->ftag, request->type);
1302
1303 END_CRIT_SECTION();
1304
1305 if (requests)
1306 pfree(requests);
1307 }
1308
1309 /*
1310 * Update any shared memory configurations based on config parameters
1311 */
1312 static void
UpdateSharedMemoryConfig(void)1313 UpdateSharedMemoryConfig(void)
1314 {
1315 /* update global shmem state for sync rep */
1316 SyncRepUpdateSyncStandbysDefined();
1317
1318 /*
1319 * If full_page_writes has been changed by SIGHUP, we update it in shared
1320 * memory and write an XLOG_FPW_CHANGE record.
1321 */
1322 UpdateFullPageWrites();
1323
1324 elog(DEBUG2, "checkpointer updated shared memory configuration values");
1325 }
1326
1327 /*
1328 * FirstCallSinceLastCheckpoint allows a process to take an action once
1329 * per checkpoint cycle by asynchronously checking for checkpoint completion.
1330 */
1331 bool
FirstCallSinceLastCheckpoint(void)1332 FirstCallSinceLastCheckpoint(void)
1333 {
1334 static int ckpt_done = 0;
1335 int new_done;
1336 bool FirstCall = false;
1337
1338 SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
1339 new_done = CheckpointerShmem->ckpt_done;
1340 SpinLockRelease(&CheckpointerShmem->ckpt_lck);
1341
1342 if (new_done != ckpt_done)
1343 FirstCall = true;
1344
1345 ckpt_done = new_done;
1346
1347 return FirstCall;
1348 }
1349