Re: Performance problems testing with Spamassassin

Alvaro,

On 7/29/05 6:23 AM, "Alvaro Herrera" <alvherre(at)alvh(dot)no-ip(dot)org> wrote:

> On Fri, Jul 29, 2005 at 03:01:07AM -0400, Luke Lonergan wrote:
>
>> I guess we see the real culprit here. Anyone surprised it's the WAL?
>
> So what? Are you planning to suggest people to turn fsync=false?

That's not the conclusion I made, no. I was pointing out that fsync has a
HUGE impact on his problem, which implies something to do with the I/O sync
operations. Black box bottleneck hunt approach #12.

> With fsync off, there's no
> work _at all_ going on, not just the WAL -- heap/index file fsync at
> checkpoint is also skipped. This is no good.

OK - so that's what Tom is pointing out, that fsync impacts more than WAL.

However, finding out that fsync/no fsync makes a 400% difference in speed
for this problem is interesting and relevant, no?

- Luke