Re: shared-memory based stats collector

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, michael(at)paquier(dot)xyz, thomas(dot)munro(at)gmail(dot)com, tomas(dot)vondra(at)2ndquadrant(dot)com, andres(at)anarazel(dot)de, a(dot)zakirov(at)postgrespro(dot)ru, ah(at)cybertec(dot)at, magnus(at)hagander(dot)net, robertmhaas(at)gmail(dot)com, pgsql-hackers(at)postgresql(dot)org
Subject: Re: shared-memory based stats collector
Date: 2020-03-09 18:37:05
Message-ID: 20200309183705.GA10363@alvherre.pgsql
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Tom Lane escribió:

In patch 0003,

> /*
> - * Was it the archiver? If so, just try to start a new one; no need
> - * to force reset of the rest of the system. (If fail, we'll try
> - * again in future cycles of the main loop.). Unless we were waiting
> - * for it to shut down; don't restart it in that case, and
> - * PostmasterStateMachine() will advance to the next shutdown step.
> + * Was it the archiver? Normal exit can be ignored; we'll start a new
> + * one at the next iteration of the postmaster's main loop, if
> + * necessary. Any other exit condition is treated as a crash.
> */
> if (pid == PgArchPID)
> {
> PgArchPID = 0;
> if (!EXIT_STATUS_0(exitstatus))
> - LogChildExit(LOG, _("archiver process"),
> - pid, exitstatus);
> - if (PgArchStartupAllowed())
> - PgArchPID = pgarch_start();
> + HandleChildCrash(pid, exitstatus,
> + _("archiver process"));
> continue;
> }

I'm worried that we're causing all processes to terminate when an
archiver dies in some ugly way; but in the current coding, it's pretty
harmless and we'd just start a new one. I think this needs to be
reconsidered. As far as I know, pgarchiver remains unconnected to
shared memory so a crash-restart cycle is not necessary. We should
continue to just log the error message and move on.

Álvaro Herrera
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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