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For cascading replication, wake physical and logical walsenders separately

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Physical walsenders can't send data until it's been flushed; logical
walsenders can't decode and send data until it's been applied. On the
standby, the WAL is flushed first, which will only wake up physical
walsenders; and then applied, which will only wake up logical
walsenders.

Previously, all walsenders were awakened when the WAL was flushed. That
was fine for logical walsenders on the primary; but on the standby the
flushed WAL would have been not applied yet, so logical walsenders were
awakened too early.

Per idea from Jeff Davis and Amit Kapila.

Author: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
Reviewed-By: Jeff Davis <pgsql@j-davis.com>
Reviewed-By: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Discussion: https://postgr.es/m/CAA4eK1+zO5LUeisabX10c81LU-fWMKO4M9Wyg1cdkbW7Hqh6vQ@mail.gmail.com
This commit is contained in:
Andres Freund
2023-04-08 00:24:24 -07:00
parent 26669757b6
commit e101dfac3a
7 changed files with 84 additions and 29 deletions
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37
src/backend/access/transam/xlogrecovery.c
View File

@@ -1935,6 +1935,31 @@ ApplyWalRecord(XLogReaderState *xlogreader, XLogRecord *record, TimeLineID *repl
XLogRecoveryCtl->lastReplayedTLI = *replayTLI;
SpinLockRelease(&XLogRecoveryCtl->info_lck);
/* ------
* Wakeup walsenders:
*
* On the standby, the WAL is flushed first (which will only wake up
* physical walsenders) and then applied, which will only wake up logical
* walsenders.
*
* Indeed, logical walsenders on standby can't decode and send data until
* it's been applied.
*
* Physical walsenders don't need to be woken up during replay unless
* cascading replication is allowed and time line change occurred (so that
* they can notice that they are on a new time line).
*
* That's why the wake up conditions are for:
*
* - physical walsenders in case of new time line and cascade
* replication is allowed
* - logical walsenders in case cascade replication is allowed (could not
* be created otherwise)
* ------
*/
if (AllowCascadeReplication())
WalSndWakeup(switchedTLI, true);
/*
* If rm_redo called XLogRequestWalReceiverReply, then we wake up the
* receiver so that it notices the updated lastReplayedEndRecPtr and sends
@@ -1958,12 +1983,6 @@ ApplyWalRecord(XLogReaderState *xlogreader, XLogRecord *record, TimeLineID *repl
*/
RemoveNonParentXlogFiles(xlogreader->EndRecPtr, *replayTLI);
/*
* Wake up any walsenders to notice that we are on a new timeline.
*/
if (AllowCascadeReplication())
WalSndWakeup();
/* Reset the prefetcher. */
XLogPrefetchReconfigure();
}
@@ -3050,9 +3069,9 @@ ReadRecord(XLogPrefetcher *xlogprefetcher, int emode,
{
/*
* When we find that WAL ends in an incomplete record, keep track
* of that record. After recovery is done, we'll write a record to
* indicate to downstream WAL readers that that portion is to be
* ignored.
* of that record. After recovery is done, we'll write a record
* to indicate to downstream WAL readers that that portion is to
* be ignored.
*
* However, when ArchiveRecoveryRequested = true, we're going to
* switch to a new timeline at the end of recovery. We will only