Re: Problem while setting the fpw with SIGHUP

From: Michael Paquier <michael(at)paquier(dot)xyz>
To: Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
Cc: dilipbalaut(at)gmail(dot)com, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Problem while setting the fpw with SIGHUP
Date: 2018-03-27 13:02:26
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On Tue, Mar 27, 2018 at 09:01:20PM +0900, Kyotaro HORIGUCHI wrote:
> The current UpdateFullPageWrites is safe on standby and promotion
> so what we should consider is only the non-standby case. I think
> what we should do is just calling RecoveryInProgress() at the
> beginning of CheckPointerMain, which is just the same thing with
> InitPostgres, but before setting up signal handler to avoid
> processing SIGHUP before being ready to insert xlog.

Your proposal does not fix the issue for a checkpointer process started
on a standby. After a promotion, if SIGHUP is issued with a change in
full_page_writes, then the initialization of InitXLogInsert() would
happen again in the critical section of UpdateFullPageWrites(). The
window is rather small for normal promotions as the startup process
requests a checkpoint which would do the initialization, and much larger
for fallback_promote where the startup process is in charge of doing the
end-of-recovery checkpoint.

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