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Commitc47f498

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Stabilize NOTIFY behavior by transmitting notifies before ReadyForQuery.
This patch ensures that, if any notify messages were received duringa just-finished transaction, they get sent to the frontend just beforenot just after the ReadyForQuery message. With libpq and other clientlibraries that act similarly, this guarantees that the client will seethe notify messages as available as soon as it thinks the transactionis done.This probably makes no difference in practice, since in realisticuse-cases the application would have to cope with asynchronousarrival of notify events anyhow. However, it makes it a lot easierto build cross-session-notify test cases with stable behavior.I'm a bit surprised now that we've not seen any buildfarm instabilitywith the test cases added by commitb10f40b. Tests that I intendto add in an upcoming bug fix are definitely unstable without this.Back-patch to 9.6, which is as far back as we can do NOTIFY testingwith the isolationtester infrastructure.Discussion:https://postgr.es/m/13881.1574557302@sss.pgh.pa.us
1 parent7d4c311 commitc47f498

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‎src/backend/commands/async.c

Lines changed: 7 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1720,11 +1720,13 @@ HandleNotifyInterrupt(void)
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/*
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* ProcessNotifyInterrupt
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*
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*This is called just after waiting for a frontend command. If a
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*interrupt arrives (via HandleNotifyInterrupt()) while reading, the
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*read will be interrupted via the process's latch, and this routine
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*will get called. If we are truly idle (ie, *not* inside a transaction
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*block), process the incoming notifies.
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*This is called if we see notifyInterruptPending set, just before
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*transmitting ReadyForQuery at the end of a frontend command, and
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*also if a notify signal occurs while reading from the frontend.
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*HandleNotifyInterrupt() will cause the read to be interrupted
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*via the process's latch, and this routine will get called.
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*If we are truly idle (ie, *not* inside a transaction block),
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*process the incoming notifies.
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*/
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void
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ProcessNotifyInterrupt(void)

‎src/backend/tcop/postgres.c

Lines changed: 11 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -4153,7 +4153,18 @@ PostgresMain(int argc, char *argv[],
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}
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else
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{
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/* Send out notify signals and transmit self-notifies */
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ProcessCompletedNotifies();
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/*
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* Also process incoming notifies, if any. This is mostly to
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* ensure stable behavior in tests: if any notifies were
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* received during the just-finished transaction, they'll be
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* seen by the client before ReadyForQuery is.
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*/
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if (notifyInterruptPending)
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ProcessNotifyInterrupt();
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pgstat_report_stat(false);
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set_ps_display("idle", false);

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