Re: wal_buffers = -1 and SIGHUP

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> 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.

Mph ... I think this shows the error of my thinking :-(. We at least
need an assign hook here. Will fix, since it was my oversight to begin
with.

regards, tom lane