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Commit73da6b8

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Refactor WaitForLSNReplay() to return the result of waiting
Currently, WaitForLSNReplay() immediately throws an error if waiting for LSNreplay is not successful. This commit teaches WaitForLSNReplay() to returnthe result of waiting, while making pg_wal_replay_wait() responsible forthrowing an appropriate error.This is preparation to adding 'no_error' argument to pg_wal_replay_wait() andnew function pg_wal_replay_wait_status(), which returns the last wait resultstatus.Additionally, we stop distinguishing situations when we find our instance tobe not in a recovery state before entering the waiting loop and insidethe waiting loop. Standby promotion may happen at any moment, even betweenissuing a procedure call statement and pg_wal_replay_wait() doing a firstcheck of recovery status. Thus, there is no pointing distinguishing thesesituations.Also, since we may exit the waiting loop and see our instance not in recoverywithout throwing an error, we need to deleteLSNWaiter() in that case. We dothis unconditionally for the sake of simplicity, even if standby was alreadypromoted after reaching the target LSN, the startup process surely alreadydeleted us.Reported-by: Michael PaquierDiscussion:https://postgr.es/m/ZtUF17gF0pNpwZDI%40paquier.xyzReviewed-by: Michael Paquier, Pavel Borisov
1 parent6cfebfe commit73da6b8

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4 files changed

+54
-24
lines changed

4 files changed

+54
-24
lines changed

‎src/backend/access/transam/xlogfuncs.c‎

Lines changed: 30 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -759,6 +759,7 @@ pg_wal_replay_wait(PG_FUNCTION_ARGS)
759759
{
760760
XLogRecPtrtarget_lsn=PG_GETARG_LSN(0);
761761
int64timeout=PG_GETARG_INT64(1);
762+
WaitLSNResultresult;
762763

763764
if (timeout<0)
764765
ereport(ERROR,
@@ -799,7 +800,35 @@ pg_wal_replay_wait(PG_FUNCTION_ARGS)
799800
*/
800801
Assert(MyProc->xmin==InvalidTransactionId);
801802

802-
(void)WaitForLSNReplay(target_lsn,timeout);
803+
result=WaitForLSNReplay(target_lsn,timeout);
804+
805+
/*
806+
* Process the result of WaitForLSNReplay(). Throw appropriate error if
807+
* needed.
808+
*/
809+
switch (result)
810+
{
811+
caseWAIT_LSN_RESULT_SUCCESS:
812+
/* Nothing to do on success */
813+
break;
814+
815+
caseWAIT_LSN_RESULT_TIMEOUT:
816+
ereport(ERROR,
817+
(errcode(ERRCODE_QUERY_CANCELED),
818+
errmsg("timed out while waiting for target LSN %X/%X to be replayed; current replay LSN %X/%X",
819+
LSN_FORMAT_ARGS(target_lsn),
820+
LSN_FORMAT_ARGS(GetXLogReplayRecPtr(NULL)))));
821+
break;
822+
823+
caseWAIT_LSN_RESULT_NOT_IN_RECOVERY:
824+
ereport(ERROR,
825+
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
826+
errmsg("recovery is not in progress"),
827+
errdetail("Recovery ended before replaying target LSN %X/%X; last replay LSN %X/%X.",
828+
LSN_FORMAT_ARGS(target_lsn),
829+
LSN_FORMAT_ARGS(GetXLogReplayRecPtr(NULL)))));
830+
break;
831+
}
803832

804833
PG_RETURN_VOID();
805834
}

‎src/backend/access/transam/xlogwait.c‎

Lines changed: 11 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -217,7 +217,7 @@ WaitLSNCleanup(void)
217217
* Wait using MyLatch till the given LSN is replayed, the postmaster dies or
218218
* timeout happens.
219219
*/
220-
void
220+
WaitLSNResult
221221
WaitForLSNReplay(XLogRecPtrtargetLSN,int64timeout)
222222
{
223223
XLogRecPtrcurrentLSN;
@@ -240,17 +240,14 @@ WaitForLSNReplay(XLogRecPtr targetLSN, int64 timeout)
240240
* check the last replay LSN before reporting an error.
241241
*/
242242
if (targetLSN <=GetXLogReplayRecPtr(NULL))
243-
return;
244-
ereport(ERROR,
245-
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
246-
errmsg("recovery is not in progress"),
247-
errhint("Waiting for LSN can only be executed during recovery.")));
243+
returnWAIT_LSN_RESULT_SUCCESS;
244+
returnWAIT_LSN_RESULT_NOT_IN_RECOVERY;
248245
}
249246
else
250247
{
251248
/* If target LSN is already replayed, exit immediately */
252249
if (targetLSN <=GetXLogReplayRecPtr(NULL))
253-
return;
250+
returnWAIT_LSN_RESULT_SUCCESS;
254251
}
255252

256253
if (timeout>0)
@@ -276,17 +273,13 @@ WaitForLSNReplay(XLogRecPtr targetLSN, int64 timeout)
276273
{
277274
/*
278275
* Recovery was ended, but recheck if target LSN was already
279-
* replayed.
276+
* replayed. See the comment regarding deleteLSNWaiter() below.
280277
*/
278+
deleteLSNWaiter();
281279
currentLSN=GetXLogReplayRecPtr(NULL);
282280
if (targetLSN <=currentLSN)
283-
return;
284-
ereport(ERROR,
285-
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
286-
errmsg("recovery is not in progress"),
287-
errdetail("Recovery ended before replaying target LSN %X/%X; last replay LSN %X/%X.",
288-
LSN_FORMAT_ARGS(targetLSN),
289-
LSN_FORMAT_ARGS(currentLSN))));
281+
returnWAIT_LSN_RESULT_SUCCESS;
282+
returnWAIT_LSN_RESULT_NOT_IN_RECOVERY;
290283
}
291284
else
292285
{
@@ -338,11 +331,7 @@ WaitForLSNReplay(XLogRecPtr targetLSN, int64 timeout)
338331
* If we didn't reach the target LSN, we must be exited by timeout.
339332
*/
340333
if (targetLSN>currentLSN)
341-
{
342-
ereport(ERROR,
343-
(errcode(ERRCODE_QUERY_CANCELED),
344-
errmsg("timed out while waiting for target LSN %X/%X to be replayed; current replay LSN %X/%X",
345-
LSN_FORMAT_ARGS(targetLSN),
346-
LSN_FORMAT_ARGS(currentLSN))));
347-
}
334+
returnWAIT_LSN_RESULT_TIMEOUT;
335+
336+
returnWAIT_LSN_RESULT_SUCCESS;
348337
}

‎src/include/access/xlogwait.h‎

Lines changed: 12 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -70,12 +70,23 @@ typedef struct WaitLSNState
7070
WaitLSNProcInfoprocInfos[FLEXIBLE_ARRAY_MEMBER];
7171
}WaitLSNState;
7272

73+
/*
74+
* Result statuses for WaitForLSNReplay().
75+
*/
76+
typedefenum
77+
{
78+
WAIT_LSN_RESULT_SUCCESS,/* Target LSN is reached */
79+
WAIT_LSN_RESULT_TIMEOUT,/* Timeout occurred */
80+
WAIT_LSN_RESULT_NOT_IN_RECOVERY,/* Recovery ended before or during our
81+
* wait */
82+
}WaitLSNResult;
83+
7384
externPGDLLIMPORTWaitLSNState*waitLSNState;
7485

7586
externSizeWaitLSNShmemSize(void);
7687
externvoidWaitLSNShmemInit(void);
7788
externvoidWaitLSNSetLatches(XLogRecPtrcurrentLSN);
7889
externvoidWaitLSNCleanup(void);
79-
externvoidWaitForLSNReplay(XLogRecPtrtargetLSN,int64timeout);
90+
externWaitLSNResultWaitForLSNReplay(XLogRecPtrtargetLSN,int64timeout);
8091

8192
#endif/* XLOG_WAIT_H */

‎src/tools/pgindent/typedefs.list‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3126,6 +3126,7 @@ WaitEventIPC
31263126
WaitEventSet
31273127
WaitEventTimeout
31283128
WaitLSNProcInfo
3129+
WaitLSNResult
31293130
WaitLSNState
31303131
WaitPMResult
31313132
WalCloseMethod

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