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Commitf32678c

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Reduce delay for last logicalrep feedback message when master goes idle.
The regression tests contain numerous cases where we do some activity on amaster server and then wait till the slave has ack'd flushing its copy ofthat transaction. Because WAL flush on the slave is asynchronous to thelogicalrep worker process, the worker cannot send such a feedback messageduring the LogicalRepApplyLoop iteration where it processes the last datafrom the master. In the previous coding, the feedback message would comeout only when the loop's WaitLatchOrSocket call returned WL_TIMEOUT. Thatrequires one full second of delay (NAPTIME_PER_CYCLE); and to add insultto injury, it could take more than that if the WaitLatchOrSocket wasinterrupted a few times by latch-setting events.In reality we can expect the slave's walwriter process to have flushed theWAL data after, more or less, WalWriterDelay (typically 200ms). Hence,if there are unacked transactions pending, make the wait delay only thatlong rather than the full NAPTIME_PER_CYCLE. Also, move one of thesend_feedback() calls into the loop main line, so that we'll check for theneed to send feedback even if we were woken by a latch event and not eithersocket data or timeout.It's not clear how much this matters for production purposes, butit's definitely helpful for testing.Discussion:https://postgr.es/m/30864.1498861103@sss.pgh.pa.us
1 parent799f8bc commitf32678c

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‎src/backend/replication/logical/worker.c

Lines changed: 16 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -52,6 +52,7 @@
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5353
#include"postmaster/bgworker.h"
5454
#include"postmaster/postmaster.h"
55+
#include"postmaster/walwriter.h"
5556

5657
#include"replication/decode.h"
5758
#include"replication/logical.h"
@@ -1027,6 +1028,7 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
10271028
boolendofstream= false;
10281029
TimestampTzlast_recv_timestamp=GetCurrentTimestamp();
10291030
boolping_sent= false;
1031+
longwait_time;
10301032

10311033
CHECK_FOR_INTERRUPTS();
10321034

@@ -1114,11 +1116,11 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
11141116

11151117
len=walrcv_receive(wrconn,&buf,&fd);
11161118
}
1117-
1118-
/* confirm all writes at once */
1119-
send_feedback(last_received, false, false);
11201119
}
11211120

1121+
/* confirm all writes so far */
1122+
send_feedback(last_received, false, false);
1123+
11221124
if (!in_remote_transaction)
11231125
{
11241126
/*
@@ -1147,12 +1149,21 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
11471149
}
11481150

11491151
/*
1150-
* Wait for more data or latch.
1152+
* Wait for more data or latch. If we have unflushed transactions,
1153+
* wake up after WalWriterDelay to see if they've been flushed yet (in
1154+
* which case we should send a feedback message). Otherwise, there's
1155+
* no particular urgency about waking up unless we get data or a
1156+
* signal.
11511157
*/
1158+
if (!dlist_is_empty(&lsn_mapping))
1159+
wait_time=WalWriterDelay;
1160+
else
1161+
wait_time=NAPTIME_PER_CYCLE;
1162+
11521163
rc=WaitLatchOrSocket(MyLatch,
11531164
WL_SOCKET_READABLE |WL_LATCH_SET |
11541165
WL_TIMEOUT |WL_POSTMASTER_DEATH,
1155-
fd,NAPTIME_PER_CYCLE,
1166+
fd,wait_time,
11561167
WAIT_EVENT_LOGICAL_APPLY_MAIN);
11571168

11581169
/* Emergency bailout if postmaster has died */

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