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Commit94ae6ba

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Send keepalives from walsender even when busy sending WAL.
If walsender doesn't hear from the client for the time specified bywal_sender_timeout, it will conclude the connection or client is dead, anddisconnect. When half of wal_sender_timeout has elapsed, it sends a pingto the client, leaving it the remainig half of wal_sender_timeout torespond. However, it only checked if half of wal_sender_timeout had elapsedwhen it was about to sleep, so if it was busy sending WAL to the client forlong enough, it would not send the ping request in time. Then the clientwould not know it needs to send a reply, and the walsender will disconnecteven though the client is still alive. Fix that.Andres Freund, reviewed by Robert Haas, and some further changes by me.Backpatch to 9.3. Earlier versions relied on the client to send thekeepalives on its own, and hence didn't have this problem.
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1 file changed

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‎src/backend/replication/walsender.c

Lines changed: 29 additions & 24 deletions
Original file line numberDiff line numberDiff line change
@@ -1258,6 +1258,27 @@ WalSndLoop(void)
12581258
}
12591259
}
12601260

1261+
/*
1262+
* If half of wal_sender_timeout has elapsed without receiving any
1263+
* reply from standby, send a keep-alive message requesting an
1264+
* immediate reply.
1265+
*/
1266+
if (wal_sender_timeout>0&& !ping_sent)
1267+
{
1268+
TimestampTztimeout;
1269+
1270+
timeout=TimestampTzPlusMilliseconds(last_reply_timestamp,
1271+
wal_sender_timeout /2);
1272+
if (GetCurrentTimestamp() >=timeout)
1273+
{
1274+
WalSndKeepalive(true);
1275+
ping_sent= true;
1276+
/* Try to flush pending output to the client */
1277+
if (pq_flush_if_writable()!=0)
1278+
gotosend_failure;
1279+
}
1280+
}
1281+
12611282
/*
12621283
* We don't block if not caught up, unless there is unsent data
12631284
* pending in which case we'd better block until the socket is
@@ -1267,7 +1288,7 @@ WalSndLoop(void)
12671288
*/
12681289
if ((caughtup&& !streamingDoneSending)||pq_is_send_pending())
12691290
{
1270-
TimestampTztimeout=0;
1291+
TimestampTztimeout;
12711292
longsleeptime=10000;/* 10 s */
12721293
intwakeEvents;
12731294

@@ -1276,32 +1297,14 @@ WalSndLoop(void)
12761297

12771298
if (pq_is_send_pending())
12781299
wakeEvents |=WL_SOCKET_WRITEABLE;
1279-
elseif (wal_sender_timeout>0&& !ping_sent)
1280-
{
1281-
/*
1282-
* If half of wal_sender_timeout has lapsed without receiving
1283-
* any reply from standby, send a keep-alive message to
1284-
* standby requesting an immediate reply.
1285-
*/
1286-
timeout=TimestampTzPlusMilliseconds(last_reply_timestamp,
1287-
wal_sender_timeout /2);
1288-
if (GetCurrentTimestamp() >=timeout)
1289-
{
1290-
WalSndKeepalive(true);
1291-
ping_sent= true;
1292-
/* Try to flush pending output to the client */
1293-
if (pq_flush_if_writable()!=0)
1294-
gotosend_failure;
1295-
}
1296-
}
12971300

1298-
/* Determine time until replication timeout */
1301+
/*
1302+
* If wal_sender_timeout is active, sleep in smaller increments
1303+
* to not go over the timeout too much. XXX: Why not just sleep
1304+
* until the timeout has elapsed?
1305+
*/
12991306
if (wal_sender_timeout>0)
1300-
{
1301-
timeout=TimestampTzPlusMilliseconds(last_reply_timestamp,
1302-
wal_sender_timeout);
13031307
sleeptime=1+ (wal_sender_timeout /10);
1304-
}
13051308

13061309
/* Sleep until something happens or we time out */
13071310
ImmediateInterruptOK= true;
@@ -1315,6 +1318,8 @@ WalSndLoop(void)
13151318
* possibility that the client replied just as we reached the
13161319
* timeout ... he's supposed to reply *before* that.
13171320
*/
1321+
timeout=TimestampTzPlusMilliseconds(last_reply_timestamp,
1322+
wal_sender_timeout);
13181323
if (wal_sender_timeout>0&&GetCurrentTimestamp() >=timeout)
13191324
{
13201325
/*

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