Re: Can a child process detect postmaster death when in pg_usleep?

From: Michael Paquier <michael(at)paquier(dot)xyz>
To: Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>
Cc: Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Can a child process detect postmaster death when in pg_usleep?
Date: 2021-07-05 02:03:12
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On Fri, Jul 02, 2021 at 12:03:07PM +0530, Bharath Rupireddy wrote:
> My bad. I was talking about the cases when do_pg_stop_backup is called
> while the server is in recovery mode i.e. backup_started_in_recovery =
> RecoveryInProgress(); evaluates to true. I'm not sure in these cases
> whether we should replace pg_usleep with WaitLatch. If yes, whether we
> should use procLatch/MyLatch or recoveryWakeupLatch as they are
> currently serving different purposes.

It seems to me that you should re-read the description of
recoveryWakeupLatch at the top of xlog.c and check for which purpose
it exists, which is, in this case, to wake up the startup process to
accelerate WAL replay. So do_pg_stop_backup() has no business with

Switching pg_stop_backup() to use a latch rather than pg_usleep() has
- It simplifies the wait event handling.
- The process waiting for the last WAL segment to be archived will be
more responsive on signals like SIGHUP and on postmaster death.

These don't sound bad to me to apply here, so 0002 could be simplified
as attached.

Attachment Content-Type Size
stop-backup-latch-v2.patch text/x-diff 688 bytes

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