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Commitee0ab27

Browse files
committed
Ignore server-side delays when enforcing wal_sender_timeout.
Healthy clients of servers having poor I/O performance, such asbuildfarm members hamster and tern, saw unexpected timeouts. Thatdisagreed with documentation. This fix adds one gettimeofday() callwhenever ProcessRepliesIfAny() finds no client reply messages.Back-patch to 9.4; the bug's symptom is rare and mild, and the code allmoved between 9.3 and 9.4.Discussion:https://postgr.es/m/20180826034600.GA1105084@rfd.leadboat.com
1 parent1f349aa commitee0ab27

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1 file changed

+36
-28
lines changed

1 file changed

+36
-28
lines changed

‎src/backend/replication/walsender.c

Lines changed: 36 additions & 28 deletions
Original file line numberDiff line numberDiff line change
@@ -162,9 +162,12 @@ static StringInfoData output_message;
162162
staticStringInfoDatareply_message;
163163
staticStringInfoDatatmpbuf;
164164

165+
/* Timestamp of last ProcessRepliesIfAny(). */
166+
staticTimestampTzlast_processing=0;
167+
165168
/*
166-
* Timestamp ofthelastreceipt of thereply from the standby. Set to 0 if
167-
* wal_sender_timeout doesn't need to be active.
169+
* Timestamp of lastProcessRepliesIfAny() that saw areply from the
170+
*standby. Set to 0 ifwal_sender_timeout doesn't need to be active.
168171
*/
169172
staticTimestampTzlast_reply_timestamp=0;
170173

@@ -241,8 +244,8 @@ static void ProcessStandbyReplyMessage(void);
241244
staticvoidProcessStandbyHSFeedbackMessage(void);
242245
staticvoidProcessRepliesIfAny(void);
243246
staticvoidWalSndKeepalive(boolrequestReply);
244-
staticvoidWalSndKeepaliveIfNecessary(TimestampTznow);
245-
staticvoidWalSndCheckTimeOut(TimestampTznow);
247+
staticvoidWalSndKeepaliveIfNecessary(void);
248+
staticvoidWalSndCheckTimeOut(void);
246249
staticlongWalSndComputeSleeptime(TimestampTznow);
247250
staticvoidWalSndPrepareWrite(LogicalDecodingContext*ctx,XLogRecPtrlsn,TransactionIdxid,boollast_write);
248251
staticvoidWalSndWriteData(LogicalDecodingContext*ctx,XLogRecPtrlsn,TransactionIdxid,boollast_write);
@@ -1195,18 +1198,16 @@ WalSndWriteData(LogicalDecodingContext *ctx, XLogRecPtr lsn, TransactionId xid,
11951198
/* Check for input from the client */
11961199
ProcessRepliesIfAny();
11971200

1198-
now=GetCurrentTimestamp();
1199-
12001201
/* die if timeout was reached */
1201-
WalSndCheckTimeOut(now);
1202+
WalSndCheckTimeOut();
12021203

12031204
/* Send keepalive if the time has come */
1204-
WalSndKeepaliveIfNecessary(now);
1205+
WalSndKeepaliveIfNecessary();
12051206

12061207
if (!pq_is_send_pending())
12071208
break;
12081209

1209-
sleeptime=WalSndComputeSleeptime(now);
1210+
sleeptime=WalSndComputeSleeptime(GetCurrentTimestamp());
12101211

12111212
wakeEvents=WL_LATCH_SET |WL_POSTMASTER_DEATH |
12121213
WL_SOCKET_WRITEABLE |WL_SOCKET_READABLE |WL_TIMEOUT;
@@ -1301,7 +1302,6 @@ WalSndWaitForWal(XLogRecPtr loc)
13011302
for (;;)
13021303
{
13031304
longsleeptime;
1304-
TimestampTznow;
13051305

13061306
/*
13071307
* Emergency bailout if postmaster has died. This is to avoid the
@@ -1386,13 +1386,11 @@ WalSndWaitForWal(XLogRecPtr loc)
13861386
!pq_is_send_pending())
13871387
break;
13881388

1389-
now=GetCurrentTimestamp();
1390-
13911389
/* die if timeout was reached */
1392-
WalSndCheckTimeOut(now);
1390+
WalSndCheckTimeOut();
13931391

13941392
/* Send keepalive if the time has come */
1395-
WalSndKeepaliveIfNecessary(now);
1393+
WalSndKeepaliveIfNecessary();
13961394

13971395
/*
13981396
* Sleep until something happens or we time out. Also wait for the
@@ -1401,7 +1399,7 @@ WalSndWaitForWal(XLogRecPtr loc)
14011399
* new WAL to be generated. (But if we have nothing to send, we don't
14021400
* want to wake on socket-writable.)
14031401
*/
1404-
sleeptime=WalSndComputeSleeptime(now);
1402+
sleeptime=WalSndComputeSleeptime(GetCurrentTimestamp());
14051403

14061404
wakeEvents=WL_LATCH_SET |WL_POSTMASTER_DEATH |
14071405
WL_SOCKET_READABLE |WL_TIMEOUT;
@@ -1598,6 +1596,8 @@ ProcessRepliesIfAny(void)
15981596
intr;
15991597
boolreceived= false;
16001598

1599+
last_processing=GetCurrentTimestamp();
1600+
16011601
for (;;)
16021602
{
16031603
pq_startmsgread();
@@ -1685,7 +1685,7 @@ ProcessRepliesIfAny(void)
16851685
*/
16861686
if (received)
16871687
{
1688-
last_reply_timestamp=GetCurrentTimestamp();
1688+
last_reply_timestamp=last_processing;
16891689
waiting_for_ping_response= false;
16901690
}
16911691
}
@@ -2064,10 +2064,18 @@ WalSndComputeSleeptime(TimestampTz now)
20642064

20652065
/*
20662066
* Check whether there have been responses by the client within
2067-
* wal_sender_timeout and shutdown if not.
2067+
* wal_sender_timeout and shutdown if not. Using last_processing as the
2068+
* reference point avoids counting server-side stalls against the client.
2069+
* However, a long server-side stall can make WalSndKeepaliveIfNecessary()
2070+
* postdate last_processing by more than wal_sender_timeout. If that happens,
2071+
* the client must reply almost immediately to avoid a timeout. This rarely
2072+
* affects the default configuration, under which clients spontaneously send a
2073+
* message every standby_message_timeout = wal_sender_timeout/6 = 10s. We
2074+
* could eliminate that problem by recognizing timeout expiration at
2075+
* wal_sender_timeout/2 after the keepalive.
20682076
*/
20692077
staticvoid
2070-
WalSndCheckTimeOut(TimestampTznow)
2078+
WalSndCheckTimeOut(void)
20712079
{
20722080
TimestampTztimeout;
20732081

@@ -2078,7 +2086,7 @@ WalSndCheckTimeOut(TimestampTz now)
20782086
timeout=TimestampTzPlusMilliseconds(last_reply_timestamp,
20792087
wal_sender_timeout);
20802088

2081-
if (wal_sender_timeout>0&&now >=timeout)
2089+
if (wal_sender_timeout>0&&last_processing >=timeout)
20822090
{
20832091
/*
20842092
* Since typically expiration of replication timeout means
@@ -2109,8 +2117,6 @@ WalSndLoop(WalSndSendDataCallback send_data)
21092117
*/
21102118
for (;;)
21112119
{
2112-
TimestampTznow;
2113-
21142120
/*
21152121
* Emergency bailout if postmaster has died. This is to avoid the
21162122
* necessity for manual cleanup of all postmaster children.
@@ -2188,13 +2194,11 @@ WalSndLoop(WalSndSendDataCallback send_data)
21882194
WalSndDone(send_data);
21892195
}
21902196

2191-
now=GetCurrentTimestamp();
2192-
21932197
/* Check for replication timeout. */
2194-
WalSndCheckTimeOut(now);
2198+
WalSndCheckTimeOut();
21952199

21962200
/* Send keepalive if the time has come */
2197-
WalSndKeepaliveIfNecessary(now);
2201+
WalSndKeepaliveIfNecessary();
21982202

21992203
/*
22002204
* We don't block if not caught up, unless there is unsent data
@@ -2212,7 +2216,11 @@ WalSndLoop(WalSndSendDataCallback send_data)
22122216
wakeEvents=WL_LATCH_SET |WL_POSTMASTER_DEATH |WL_TIMEOUT |
22132217
WL_SOCKET_READABLE;
22142218

2215-
sleeptime=WalSndComputeSleeptime(now);
2219+
/*
2220+
* Use fresh timestamp, not last_processed, to reduce the chance
2221+
* of reaching wal_sender_timeout before sending a keepalive.
2222+
*/
2223+
sleeptime=WalSndComputeSleeptime(GetCurrentTimestamp());
22162224

22172225
if (pq_is_send_pending())
22182226
wakeEvents |=WL_SOCKET_WRITEABLE;
@@ -3364,7 +3372,7 @@ WalSndKeepalive(bool requestReply)
33643372
* Send keepalive message if too much time has elapsed.
33653373
*/
33663374
staticvoid
3367-
WalSndKeepaliveIfNecessary(TimestampTznow)
3375+
WalSndKeepaliveIfNecessary(void)
33683376
{
33693377
TimestampTzping_time;
33703378

@@ -3385,7 +3393,7 @@ WalSndKeepaliveIfNecessary(TimestampTz now)
33853393
*/
33863394
ping_time=TimestampTzPlusMilliseconds(last_reply_timestamp,
33873395
wal_sender_timeout /2);
3388-
if (now >=ping_time)
3396+
if (last_processing >=ping_time)
33893397
{
33903398
WalSndKeepalive(true);
33913399
waiting_for_ping_response= true;

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