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Re: [HACKERS] fsync method checking

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Kurt Roeckx <Q(at)ping(dot)be>
Cc: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>,Mark Kirkwood <markir(at)paradise(dot)net(dot)nz>,pgsql-performance(at)postgresql(dot)org,PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] fsync method checking
Date: 2004-03-18 20:20:23
Message-ID: 11816.1079641223@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-performance
Kurt Roeckx <Q(at)ping(dot)be> writes:
> I have no idea what the access pattern is for normal WAL
> operations or how many times it gets synched.  Does it only do
> f(data)sync() at commit time, or for every block it writes?

If we are using fsync/fdatasync, we issue those at commit time or when
completing a WAL segment.  If we are using the open flags, then of
course there's no separate sync call.

My previous point about checking different fsync spacings corresponds to
different assumptions about average transaction size.  I think a useful
tool for determining wal_sync_method has got to be able to reflect that
range of possibilities.

			regards, tom lane

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