Re: WAL Bypass for indexes

Tom Lane wrote:

> [ scratches head ... ] Actually, I'd have expected that you could still
> measure a difference. I thought it might be reduced to the point where
> we arguably shouldn't spend major effort on eliminating it. But no
> difference at all really does not compute.

I agree completely and was baffled by the observations. I will do some more testing tonight to see if I can pin things down.

My machine is a cheapo Wal-Mart Compaq Presario, Sempron 3000+ (2Ghz, socket A, 512KB cache), 768 MB, with the stock 40 GB IDE drive mirrored to a 160 GB SATA drive.

I run Mandrake 2006 with the latest patches and ran the Pg snapshot with all of the defaults.

I should have seen a difference in speed, but did not. One possible explanation is that both tests had the TPS flopping around between 185 and 225. It is possible that the improvement was so small compared to the variance that it was hard to see. I will run multiple tests and post the actual numbers.

Cheers,
M

_____ Original message _____
Subject: Re: [HACKERS] WAL Bypass for indexes
Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Date: 02nd April 2006 10:48:19 PM

"Martin Scholes" <marty(at)iicolo(dot)com> writes:
> Ok Tom, I stand corrected.

> I downloaded the latest snapshot and both scenarios (normal and WAL bypass =
> for indexes) produced between 185 and 230 tps on my machine.

> The lesson here is that whatever WAL magic has been performed on the latest =
> release gives over 100% speedup, and the speedup is so good that skipping =
> WAL for indexes does basically nothing.

[ scratches head ... ] Actually, I'd have expected that you could still
measure a difference. I thought it might be reduced to the point where
we arguably shouldn't spend major effort on eliminating it. But no
difference at all really does not compute. Could you recheck your test
conditions? You still haven't been very clear what they are.

regards, tom lane

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