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Commit081e410

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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 parent4a9a5bb commit081e410

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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
@@ -154,9 +154,12 @@ static StringInfoData output_message;
154154
staticStringInfoDatareply_message;
155155
staticStringInfoDatatmpbuf;
156156

157+
/* Timestamp of last ProcessRepliesIfAny(). */
158+
staticTimestampTzlast_processing=0;
159+
157160
/*
158-
* Timestamp ofthelastreceipt of thereply from the standby. Set to 0 if
159-
* wal_sender_timeout doesn't need to be active.
161+
* Timestamp of lastProcessRepliesIfAny() that saw areply from the
162+
*standby. Set to 0 ifwal_sender_timeout doesn't need to be active.
160163
*/
161164
staticTimestampTzlast_reply_timestamp=0;
162165

@@ -213,8 +216,8 @@ static void ProcessStandbyReplyMessage(void);
213216
staticvoidProcessStandbyHSFeedbackMessage(void);
214217
staticvoidProcessRepliesIfAny(void);
215218
staticvoidWalSndKeepalive(boolrequestReply);
216-
staticvoidWalSndKeepaliveIfNecessary(TimestampTznow);
217-
staticvoidWalSndCheckTimeOut(TimestampTznow);
219+
staticvoidWalSndKeepaliveIfNecessary(void);
220+
staticvoidWalSndCheckTimeOut(void);
218221
staticlongWalSndComputeSleeptime(TimestampTznow);
219222
staticvoidWalSndPrepareWrite(LogicalDecodingContext*ctx,XLogRecPtrlsn,TransactionIdxid,boollast_write);
220223
staticvoidWalSndWriteData(LogicalDecodingContext*ctx,XLogRecPtrlsn,TransactionIdxid,boollast_write);
@@ -1117,18 +1120,16 @@ WalSndWriteData(LogicalDecodingContext *ctx, XLogRecPtr lsn, TransactionId xid,
11171120
/* Check for input from the client */
11181121
ProcessRepliesIfAny();
11191122

1120-
now=GetCurrentTimestamp();
1121-
11221123
/* die if timeout was reached */
1123-
WalSndCheckTimeOut(now);
1124+
WalSndCheckTimeOut();
11241125

11251126
/* Send keepalive if the time has come */
1126-
WalSndKeepaliveIfNecessary(now);
1127+
WalSndKeepaliveIfNecessary();
11271128

11281129
if (!pq_is_send_pending())
11291130
break;
11301131

1131-
sleeptime=WalSndComputeSleeptime(now);
1132+
sleeptime=WalSndComputeSleeptime(GetCurrentTimestamp());
11321133

11331134
wakeEvents=WL_LATCH_SET |WL_POSTMASTER_DEATH |
11341135
WL_SOCKET_WRITEABLE |WL_SOCKET_READABLE |WL_TIMEOUT;
@@ -1198,7 +1199,6 @@ WalSndWaitForWal(XLogRecPtr loc)
11981199
for (;;)
11991200
{
12001201
longsleeptime;
1201-
TimestampTznow;
12021202

12031203
/*
12041204
* Emergency bailout if postmaster has died. This is to avoid the
@@ -1283,13 +1283,11 @@ WalSndWaitForWal(XLogRecPtr loc)
12831283
!pq_is_send_pending())
12841284
break;
12851285

1286-
now=GetCurrentTimestamp();
1287-
12881286
/* die if timeout was reached */
1289-
WalSndCheckTimeOut(now);
1287+
WalSndCheckTimeOut();
12901288

12911289
/* Send keepalive if the time has come */
1292-
WalSndKeepaliveIfNecessary(now);
1290+
WalSndKeepaliveIfNecessary();
12931291

12941292
/*
12951293
* Sleep until something happens or we time out. Also wait for the
@@ -1298,7 +1296,7 @@ WalSndWaitForWal(XLogRecPtr loc)
12981296
* new WAL to be generated. (But if we have nothing to send, we don't
12991297
* want to wake on socket-writable.)
13001298
*/
1301-
sleeptime=WalSndComputeSleeptime(now);
1299+
sleeptime=WalSndComputeSleeptime(GetCurrentTimestamp());
13021300

13031301
wakeEvents=WL_LATCH_SET |WL_POSTMASTER_DEATH |
13041302
WL_SOCKET_READABLE |WL_TIMEOUT;
@@ -1438,6 +1436,8 @@ ProcessRepliesIfAny(void)
14381436
intr;
14391437
boolreceived= false;
14401438

1439+
last_processing=GetCurrentTimestamp();
1440+
14411441
for (;;)
14421442
{
14431443
pq_startmsgread();
@@ -1525,7 +1525,7 @@ ProcessRepliesIfAny(void)
15251525
*/
15261526
if (received)
15271527
{
1528-
last_reply_timestamp=GetCurrentTimestamp();
1528+
last_reply_timestamp=last_processing;
15291529
waiting_for_ping_response= false;
15301530
}
15311531
}
@@ -1818,10 +1818,18 @@ WalSndComputeSleeptime(TimestampTz now)
18181818

18191819
/*
18201820
* Check whether there have been responses by the client within
1821-
* wal_sender_timeout and shutdown if not.
1821+
* wal_sender_timeout and shutdown if not. Using last_processing as the
1822+
* reference point avoids counting server-side stalls against the client.
1823+
* However, a long server-side stall can make WalSndKeepaliveIfNecessary()
1824+
* postdate last_processing by more than wal_sender_timeout. If that happens,
1825+
* the client must reply almost immediately to avoid a timeout. This rarely
1826+
* affects the default configuration, under which clients spontaneously send a
1827+
* message every standby_message_timeout = wal_sender_timeout/6 = 10s. We
1828+
* could eliminate that problem by recognizing timeout expiration at
1829+
* wal_sender_timeout/2 after the keepalive.
18221830
*/
18231831
staticvoid
1824-
WalSndCheckTimeOut(TimestampTznow)
1832+
WalSndCheckTimeOut(void)
18251833
{
18261834
TimestampTztimeout;
18271835

@@ -1832,7 +1840,7 @@ WalSndCheckTimeOut(TimestampTz now)
18321840
timeout=TimestampTzPlusMilliseconds(last_reply_timestamp,
18331841
wal_sender_timeout);
18341842

1835-
if (wal_sender_timeout>0&&now >=timeout)
1843+
if (wal_sender_timeout>0&&last_processing >=timeout)
18361844
{
18371845
/*
18381846
* Since typically expiration of replication timeout means
@@ -1863,8 +1871,6 @@ WalSndLoop(WalSndSendDataCallback send_data)
18631871
*/
18641872
for (;;)
18651873
{
1866-
TimestampTznow;
1867-
18681874
/*
18691875
* Emergency bailout if postmaster has died. This is to avoid the
18701876
* necessity for manual cleanup of all postmaster children.
@@ -1942,13 +1948,11 @@ WalSndLoop(WalSndSendDataCallback send_data)
19421948
WalSndDone(send_data);
19431949
}
19441950

1945-
now=GetCurrentTimestamp();
1946-
19471951
/* Check for replication timeout. */
1948-
WalSndCheckTimeOut(now);
1952+
WalSndCheckTimeOut();
19491953

19501954
/* Send keepalive if the time has come */
1951-
WalSndKeepaliveIfNecessary(now);
1955+
WalSndKeepaliveIfNecessary();
19521956

19531957
/*
19541958
* We don't block if not caught up, unless there is unsent data
@@ -1966,7 +1970,11 @@ WalSndLoop(WalSndSendDataCallback send_data)
19661970
wakeEvents=WL_LATCH_SET |WL_POSTMASTER_DEATH |WL_TIMEOUT |
19671971
WL_SOCKET_READABLE;
19681972

1969-
sleeptime=WalSndComputeSleeptime(now);
1973+
/*
1974+
* Use fresh timestamp, not last_processed, to reduce the chance
1975+
* of reaching wal_sender_timeout before sending a keepalive.
1976+
*/
1977+
sleeptime=WalSndComputeSleeptime(GetCurrentTimestamp());
19701978

19711979
if (pq_is_send_pending())
19721980
wakeEvents |=WL_SOCKET_WRITEABLE;
@@ -3037,7 +3045,7 @@ WalSndKeepalive(bool requestReply)
30373045
* Send keepalive message if too much time has elapsed.
30383046
*/
30393047
staticvoid
3040-
WalSndKeepaliveIfNecessary(TimestampTznow)
3048+
WalSndKeepaliveIfNecessary(void)
30413049
{
30423050
TimestampTzping_time;
30433051

@@ -3058,7 +3066,7 @@ WalSndKeepaliveIfNecessary(TimestampTz now)
30583066
*/
30593067
ping_time=TimestampTzPlusMilliseconds(last_reply_timestamp,
30603068
wal_sender_timeout /2);
3061-
if (now >=ping_time)
3069+
if (last_processing >=ping_time)
30623070
{
30633071
WalSndKeepalive(true);
30643072
waiting_for_ping_response= true;

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