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Re: wal_buffers = -1 and SIGHUP

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Bernd Helmle <mailings(at)oopsware(dot)de>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: wal_buffers = -1 and SIGHUP
Date: 2011-03-31 20:00:57
Message-ID: AANLkTin4o+eSgQsP=0i6EM=Evu3oX=ewHp8Bwod1UaWZ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Thu, Mar 31, 2011 at 8:38 AM, Bernd Helmle <mailings(at)oopsware(dot)de> wrote:
> This might be nitpicking (or i'm currently missing something), but i
> recognized that setting wal_buffers = -1 always triggers the following on
> reload, even if nothing to wal_buffers had changed:
>
> $ pg_ctl reload
> LOG:  received SIGHUP, reloading configuration files
> LOG:  parameter "wal_buffers" cannot be changed without restarting the
> server
>
> This only happens when you have wal_buffers set to -1.

This is a bug.  The root cause is that, on startup, we do this:

        if (xbuffers != XLOGbuffers)
        {
                snprintf(buf, sizeof(buf), "%d", xbuffers);
                SetConfigOption("wal_buffers", buf, PGC_POSTMASTER,
PGC_S_OVERRIDE);
        }

I had intended to commit Greg's patch with a show hook and an assign
hook and the calculated value stored separately from the GUC variable,
which I believe would avoid this is a problem, but Tom thought this
way was better.  Unfortunately, my knowledge of the GUC machinery is
insufficient to think of a way to avoid it, other than the one Tom
already rejected.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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