Re: Potential Large Performance Gain in WAL synching

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Curtis Faith" <curtis(at)galtair(dot)com>
Cc: "Pgsql-Hackers" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Potential Large Performance Gain in WAL synching
Date: 2002-10-03 23:17:24
Message-ID: 15318.1033687044@sss.pgh.pa.us
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"Curtis Faith" <curtis(at)galtair(dot)com> writes:
> So, why don't we use files opened with O_DSYNC | O_APPEND for the WAL log
> and then use aio_write for all log writes?

We already offer an O_DSYNC option. It's not obvious to me what
aio_write brings to the table (aside from loss of portability).
You still have to wait for the final write to complete, no?

> 2) Allow transactions to complete and do work while other threads are
> waiting on the completion of the log write.

I'm missing something. There is no useful work that a transaction can
do between writing its commit record and reporting completion, is there?
It has to wait for that record to hit disk.

regards, tom lane

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