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Commitf83b599

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Make walsender more responsive.
Per testing by Andres Freund, this improves replication performanceand reduces replication latency and latency jitter. I was a bitconcerned about moving more work into XLogInsert, but testing seemsto show that it's not a problem in practice.Along the way, improve comments for WaitLatchOrSocket.Andres Freund. Review and stylistic cleanup by me.
1 parent9ad45c1 commitf83b599

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7 files changed

+59
-36
lines changed

7 files changed

+59
-36
lines changed

‎src/backend/access/transam/twophase.c

Lines changed: 0 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -1042,13 +1042,6 @@ EndPrepare(GlobalTransaction gxact)
10421042

10431043
/* If we crash now, we have prepared: WAL replay will fix things */
10441044

1045-
/*
1046-
* Wake up all walsenders to send WAL up to the PREPARE record immediately
1047-
* if replication is enabled
1048-
*/
1049-
if (max_wal_senders>0)
1050-
WalSndWakeup();
1051-
10521045
/* write correct CRC and close file */
10531046
if ((write(fd,&statefile_crc,sizeof(pg_crc32)))!=sizeof(pg_crc32))
10541047
{
@@ -2045,13 +2038,6 @@ RecordTransactionCommitPrepared(TransactionId xid,
20452038
/* Flush XLOG to disk */
20462039
XLogFlush(recptr);
20472040

2048-
/*
2049-
* Wake up all walsenders to send WAL up to the COMMIT PREPARED record
2050-
* immediately if replication is enabled
2051-
*/
2052-
if (max_wal_senders>0)
2053-
WalSndWakeup();
2054-
20552041
/* Mark the transaction committed in pg_clog */
20562042
TransactionIdCommitTree(xid,nchildren,children);
20572043

@@ -2132,13 +2118,6 @@ RecordTransactionAbortPrepared(TransactionId xid,
21322118
/* Always flush, since we're about to remove the 2PC state file */
21332119
XLogFlush(recptr);
21342120

2135-
/*
2136-
* Wake up all walsenders to send WAL up to the ABORT PREPARED record
2137-
* immediately if replication is enabled
2138-
*/
2139-
if (max_wal_senders>0)
2140-
WalSndWakeup();
2141-
21422121
/*
21432122
* Mark the transaction aborted in clog. This is not absolutely necessary
21442123
* but we may as well do it while we are here.

‎src/backend/access/transam/xact.c

Lines changed: 0 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -1141,13 +1141,6 @@ RecordTransactionCommit(void)
11411141

11421142
XLogFlush(XactLastRecEnd);
11431143

1144-
/*
1145-
* Wake up all walsenders to send WAL up to the COMMIT record
1146-
* immediately if replication is enabled
1147-
*/
1148-
if (max_wal_senders>0)
1149-
WalSndWakeup();
1150-
11511144
/*
11521145
* Now we may update the CLOG, if we wrote a COMMIT record above
11531146
*/

‎src/backend/access/transam/xlog.c

Lines changed: 18 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -1025,6 +1025,8 @@ begin:;
10251025

10261026
END_CRIT_SECTION();
10271027

1028+
/* wakeup the WalSnd now that we released the WALWriteLock */
1029+
WalSndWakeupProcessRequests();
10281030
returnRecPtr;
10291031
}
10301032

@@ -1208,6 +1210,9 @@ begin:;
12081210

12091211
END_CRIT_SECTION();
12101212

1213+
/* wakeup the WalSnd now that we outside contented locks */
1214+
WalSndWakeupProcessRequests();
1215+
12111216
returnRecPtr;
12121217
}
12131218

@@ -1792,6 +1797,10 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible, bool xlog_switch)
17921797
if (finishing_seg|| (xlog_switch&&last_iteration))
17931798
{
17941799
issue_xlog_fsync(openLogFile,openLogSegNo);
1800+
1801+
/* signal that we need to wakeup WalSnd later */
1802+
WalSndWakeupRequest();
1803+
17951804
LogwrtResult.Flush=LogwrtResult.Write;/* end of page */
17961805

17971806
if (XLogArchivingActive())
@@ -1854,7 +1863,11 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible, bool xlog_switch)
18541863
openLogFile=XLogFileOpen(openLogSegNo);
18551864
openLogOff=0;
18561865
}
1866+
18571867
issue_xlog_fsync(openLogFile,openLogSegNo);
1868+
1869+
/* signal that we need to wakeup WalSnd later */
1870+
WalSndWakeupRequest();
18581871
}
18591872
LogwrtResult.Flush=LogwrtResult.Write;
18601873
}
@@ -2120,6 +2133,9 @@ XLogFlush(XLogRecPtr record)
21202133

21212134
END_CRIT_SECTION();
21222135

2136+
/* wakeup the WalSnd now that we released the WALWriteLock */
2137+
WalSndWakeupProcessRequests();
2138+
21232139
/*
21242140
* If we still haven't flushed to the request point then we have a
21252141
* problem; most likely, the requested flush point is past end of XLOG.
@@ -2245,13 +2261,8 @@ XLogBackgroundFlush(void)
22452261

22462262
END_CRIT_SECTION();
22472263

2248-
/*
2249-
* If we wrote something then we have something to send to standbys also,
2250-
* otherwise the replication delay become around 7s with just async
2251-
* commit.
2252-
*/
2253-
if (wrote_something)
2254-
WalSndWakeup();
2264+
/* wakeup the WalSnd now that we released the WALWriteLock */
2265+
WalSndWakeupProcessRequests();
22552266

22562267
returnwrote_something;
22572268
}

‎src/backend/port/unix_latch.c

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -418,6 +418,9 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
418418
* NB: when calling this in a signal handler, be sure to save and restore
419419
* errno around it. (That's standard practice in most signal handlers, of
420420
* course, but we used to omit it in handlers that only set a flag.)
421+
*
422+
* NB: this function is called from critical sections and signal handlers so
423+
* throwing an error is not a good idea.
421424
*/
422425
void
423426
SetLatch(volatileLatch*latch)

‎src/backend/port/win32_latch.c

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -247,6 +247,10 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
247247
returnresult;
248248
}
249249

250+
/*
251+
* The comments above the unix implementation (unix_latch.c) of this function
252+
* apply here as well.
253+
*/
250254
void
251255
SetLatch(volatileLatch*latch)
252256
{

‎src/backend/replication/walsender.c

Lines changed: 10 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -81,6 +81,10 @@ boolam_cascading_walsender = false;/* Am I cascading WAL to
8181
intmax_wal_senders=0;/* the maximum number of concurrent walsenders */
8282
intreplication_timeout=60*1000;/* maximum time to send one
8383
* WAL data message */
84+
/*
85+
* State for WalSndWakeupRequest
86+
*/
87+
boolwake_wal_senders= false;
8488

8589
/*
8690
* These variables are used similarly to openLogFile/Id/Seg/Off,
@@ -1395,7 +1399,12 @@ WalSndShmemInit(void)
13951399
}
13961400
}
13971401

1398-
/* Wake up all walsenders */
1402+
/*
1403+
* Wake up all walsenders
1404+
*
1405+
* This will be called inside critical sections, so throwing an error is not
1406+
* adviseable.
1407+
*/
13991408
void
14001409
WalSndWakeup(void)
14011410
{

‎src/include/replication/walsender.h

Lines changed: 24 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -21,6 +21,7 @@ extern bool am_walsender;
2121
externboolam_cascading_walsender;
2222
externvolatilesig_atomic_twalsender_shutdown_requested;
2323
externvolatilesig_atomic_twalsender_ready_to_stop;
24+
externboolwake_wal_senders;
2425

2526
/* user-settable parameters */
2627
externintmax_wal_senders;
@@ -35,4 +36,27 @@ extern void WalSndRqstFileReload(void);
3536

3637
externDatumpg_stat_get_wal_senders(PG_FUNCTION_ARGS);
3738

39+
/*
40+
* Remember that we want to wakeup walsenders later
41+
*
42+
* This is separated from doing the actual wakeup because the writeout is done
43+
* while holding contended locks.
44+
*/
45+
#defineWalSndWakeupRequest() \
46+
do { wake_wal_senders = true; } while (0)
47+
48+
/*
49+
* wakeup walsenders if there is work to be done
50+
*/
51+
#defineWalSndWakeupProcessRequests()\
52+
do\
53+
{\
54+
if (wake_wal_senders)\
55+
{\
56+
wake_wal_senders = false;\
57+
if (max_wal_senders > 0)\
58+
WalSndWakeup();\
59+
}\
60+
} while (0)
61+
3862
#endif/* _WALSENDER_H */

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