From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Curtis Faith <curtis(at)galtair(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Pgsql-Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Potential Large Performance Gain in WAL synching |
Date: | 2002-10-04 15:48:33 |
Message-ID: | 200210041548.g94FmXx06991@candle.pha.pa.us |
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Lists: | pgsql-hackers |
Curtis Faith wrote:
> Bruce Momjian wrote:
> > I may be missing something here, but other backends don't block while
> > one writes to WAL.
>
> I don't think they'll block until they get to the fsync or XLogWrite
> call while another transaction is fsync'ing.
>
> I'm no Unix filesystem expert but I don't see how the OS can
> handle multiple writes and fsyncs to the same file descriptors without
> blocking other processes from writing at the same time. It may be that
> there are some clever data structures they use but I've not seen huge
> praise for most of the file systems. A well written file system could
> minimize this contention but I'll bet it's there with most of the ones
> that PostgreSQL most commonly runs on.
>
> I'll have to write a test and see if there really is a problem.
Yes, I can see some contention, but what does aio solve?
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
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