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Commitdf3737a

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Remove pg_backup_start_callback and reuse similar code
We had two copies of almost identical logic to revert shared memorystate when a running backup aborts; we can removepg_backup_start_callback if we adapt do_pg_abort_backup so that it canbe used for this purpose too.However, in order for this to work, we have to repurpose the flag passedto do_pg_abort_backup. It used to indicate whether to throw a warning(and the only caller always passed true). It now indicates whether thecallback is being called at start time (in which case the session backupstate is known not to have been set to RUNNING yet, so action is alwaystaken) or shmem time (in which case action is only taken if the sessionbackup state is RUNNING). Thus the meaning of the flag is no longersuperfluous, but it's actually quite critical to get right. I (Álvaro)chose to change the polarity and the code flow re. the flag from whatBharath submitted, for coding clarity.Co-authored-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>Discussion:https://www.postgresql.org/message-id/20221013111330.564fk5tkwe3ha77l%40alvherre.pgsql
1 parent9668c4a commitdf3737a

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1 file changed

+35
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lines changed
  • src/backend/access/transam

1 file changed

+35
-46
lines changed

‎src/backend/access/transam/xlog.c

Lines changed: 35 additions & 46 deletions
Original file line numberDiff line numberDiff line change
@@ -679,8 +679,6 @@ static void ReadControlFile(void);
679679
staticvoidUpdateControlFile(void);
680680
staticchar*str_time(pg_time_ttnow);
681681

682-
staticvoidpg_backup_start_callback(intcode,Datumarg);
683-
684682
staticintget_sync_bit(intmethod);
685683

686684
staticvoidCopyXLogRecordToWAL(intwrite_len,boolisLogSwitch,
@@ -8271,7 +8269,7 @@ void
82718269
do_pg_backup_start(constchar*backupidstr,boolfast,List**tablespaces,
82728270
BackupState*state,StringInfotblspcmapfile)
82738271
{
8274-
boolbackup_started_in_recovery= false;
8272+
boolbackup_started_in_recovery;
82758273

82768274
Assert(state!=NULL);
82778275
backup_started_in_recovery=RecoveryInProgress();
@@ -8320,8 +8318,12 @@ do_pg_backup_start(const char *backupidstr, bool fast, List **tablespaces,
83208318
XLogCtl->Insert.forcePageWrites= true;
83218319
WALInsertLockRelease();
83228320

8323-
/* Ensure we release forcePageWrites if fail below */
8324-
PG_ENSURE_ERROR_CLEANUP(pg_backup_start_callback, (Datum)0);
8321+
/*
8322+
* Ensure we release forcePageWrites if fail below. NB -- for this to work
8323+
* correctly, it is critical that sessionBackupState is only updated after
8324+
* this block is over.
8325+
*/
8326+
PG_ENSURE_ERROR_CLEANUP(do_pg_abort_backup,DatumGetBool(true));
83258327
{
83268328
boolgotUniqueStartpoint= false;
83278329
DIR*tblspcdir;
@@ -8531,7 +8533,7 @@ do_pg_backup_start(const char *backupidstr, bool fast, List **tablespaces,
85318533

85328534
state->starttime= (pg_time_t)time(NULL);
85338535
}
8534-
PG_END_ENSURE_ERROR_CLEANUP(pg_backup_start_callback, (Datum)0);
8536+
PG_END_ENSURE_ERROR_CLEANUP(do_pg_abort_backup,DatumGetBool(true));
85358537

85368538
state->started_in_recovery=backup_started_in_recovery;
85378539

@@ -8541,23 +8543,6 @@ do_pg_backup_start(const char *backupidstr, bool fast, List **tablespaces,
85418543
sessionBackupState=SESSION_BACKUP_RUNNING;
85428544
}
85438545

8544-
/* Error cleanup callback for pg_backup_start */
8545-
staticvoid
8546-
pg_backup_start_callback(intcode,Datumarg)
8547-
{
8548-
/* Update backup counters and forcePageWrites on failure */
8549-
WALInsertLockAcquireExclusive();
8550-
8551-
Assert(XLogCtl->Insert.runningBackups>0);
8552-
XLogCtl->Insert.runningBackups--;
8553-
8554-
if (XLogCtl->Insert.runningBackups==0)
8555-
{
8556-
XLogCtl->Insert.forcePageWrites= false;
8557-
}
8558-
WALInsertLockRelease();
8559-
}
8560-
85618546
/*
85628547
* Utility routine to fetch the session-level status of a backup running.
85638548
*/
@@ -8850,38 +8835,42 @@ do_pg_backup_stop(BackupState *state, bool waitforarchive)
88508835
* system out of backup mode, thus making it a lot more safe to call from
88518836
* an error handler.
88528837
*
8853-
* The caller can pass 'arg' as 'true' or 'false' to control whether a warning
8854-
* is emitted.
8838+
* 'arg' indicates that it's being called during backup setup; so
8839+
* sessionBackupState has not been modified yet, but runningBackups has
8840+
* already been incremented. When it's false, then it's invoked as a
8841+
* before_shmem_exit handler, and therefore we must not change state
8842+
* unless sessionBackupState indicates that a backup is actually running.
88558843
*
8856-
* NB: This gets used as abefore_shmem_exit handler, hence the odd-looking
8857-
* signature.
8844+
* NB: This gets used as aPG_ENSURE_ERROR_CLEANUP callback and
8845+
*before_shmem_exit handler, hence the odd-lookingsignature.
88588846
*/
88598847
void
88608848
do_pg_abort_backup(intcode,Datumarg)
88618849
{
8862-
boolemit_warning=DatumGetBool(arg);
8850+
boolduring_backup_start=DatumGetBool(arg);
88638851

8864-
/*
8865-
* Quick exit if session does not have a running backup.
8866-
*/
8867-
if (sessionBackupState!=SESSION_BACKUP_RUNNING)
8868-
return;
8852+
/* Only one of these conditions can be true */
8853+
Assert(during_backup_start ^
8854+
(sessionBackupState==SESSION_BACKUP_RUNNING));
88698855

8870-
WALInsertLockAcquireExclusive();
8871-
Assert(XLogCtl->Insert.runningBackups>0);
8872-
XLogCtl->Insert.runningBackups--;
8873-
8874-
if (XLogCtl->Insert.runningBackups==0)
8856+
if (during_backup_start||sessionBackupState!=SESSION_BACKUP_NONE)
88758857
{
8876-
XLogCtl->Insert.forcePageWrites= false;
8877-
}
8858+
WALInsertLockAcquireExclusive();
8859+
Assert(XLogCtl->Insert.runningBackups>0);
8860+
XLogCtl->Insert.runningBackups--;
88788861

8879-
sessionBackupState=SESSION_BACKUP_NONE;
8880-
WALInsertLockRelease();
8862+
if (XLogCtl->Insert.runningBackups==0)
8863+
{
8864+
XLogCtl->Insert.forcePageWrites= false;
8865+
}
8866+
8867+
sessionBackupState=SESSION_BACKUP_NONE;
8868+
WALInsertLockRelease();
88818869

8882-
if (emit_warning)
8883-
ereport(WARNING,
8884-
(errmsg("aborting backup due to backend exiting before pg_backup_stop was called")));
8870+
if (!during_backup_start)
8871+
ereport(WARNING,
8872+
errmsg("aborting backup due to backend exiting before pg_backup_stop was called"));
8873+
}
88858874
}
88868875

88878876
/*
@@ -8895,7 +8884,7 @@ register_persistent_abort_backup_handler(void)
88958884

88968885
if (already_done)
88978886
return;
8898-
before_shmem_exit(do_pg_abort_backup,DatumGetBool(true));
8887+
before_shmem_exit(do_pg_abort_backup,DatumGetBool(false));
88998888
already_done= true;
89008889
}
89018890

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