Re: Piggybacking vacuum I/O

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com>
Cc: "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Piggybacking vacuum I/O
Date: 2007-01-24 07:12:49
Message-ID: 23170.1169622769@sss.pgh.pa.us
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"Pavan Deolasee" <pavan(dot)deolasee(at)gmail(dot)com> writes:
> On a typical desktop class 2 CPU Dell machine, we have seen pgbench
> clocking more than 1500 tps.

Only if you had fsync off, or equivalently a disk drive that lies about
write-complete. You could possibly achieve such rates in a non-broken
configuration with a battery-backed write cache, but that's not "typical
desktop" kit.

In any case, you ignored Heikki's point that the PG shared memory pages
holding CLOG are unlikely to be the sole level of caching, if the update
rate is that high. The kernel will have some pages too. And even if we
thought not, wouldn't bumping the size of the clog cache be a far
simpler solution offering benefit for more things than just this?

regards, tom lane

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