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Revert "Get rid of the dedicated latch for signaling the startup process".

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Revert ac22929a26, as well as the followup fix 113d3591b8. Because it broke
the assumption that the startup process waiting for the recovery conflict
on buffer pin should be waken up only by buffer unpin or the timeout enabled
in ResolveRecoveryConflictWithBufferPin(). It caused, for example,
SIGHUP signal handler or walreceiver process to wake that startup process
up unnecessarily frequently.

Additionally, add the comments about why that dedicated latch that
the reverted patch tried to get rid of should not be removed.

Thanks to Kyotaro Horiguchi for the discussion.

Author: Fujii Masao
Discussion: https://postgr.es/m/d8c0c608-021b-3c73-fffd-3240829ee986@oss.nttdata.com
This commit is contained in:
Fujii Masao
2020-12-17 18:06:51 +09:00
parent 88e014c149
commit 00f690a239
3 changed files with 52 additions and 21 deletions
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9
src/backend/storage/ipc/standby.c
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@@ -519,7 +519,14 @@ ResolveRecoveryConflictWithBufferPin(void)
enable_timeouts(timeouts, 2);
}
/* Wait to be signaled by UnpinBuffer() */
/*
* Wait to be signaled by UnpinBuffer().
*
* We assume that only UnpinBuffer() and the timeout requests established
* above can wake us up here. WakeupRecovery() called by walreceiver or
* SIGHUP signal handler, etc cannot do that because it uses the different
* latch from that ProcWaitForSignal() waits on.
*/
ProcWaitForSignal(PG_WAIT_BUFFER_PIN);
/*