| From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
|---|---|
| To: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: 8.2 is 30% better in pgbench than 8.3 |
| Date: | 2007-07-23 17:05:40 |
| Message-ID: | 20070723170540.GK2540@alvh.no-ip.org |
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| Lists: | pgsql-hackers |
Pavan Deolasee wrote:
> On 7/23/07, Alvaro Herrera <alvherre(at)commandprompt(dot)com> wrote:
>> Certainly it doesn't prevent starvation completely -- really there is no
>> way to completely prevent starvation unless you have as many workers as
>> you have tables, and one disk for each. What DSM does do is let the big
>> tables be vacuumed quickly which makes most of the problem go away.
>
> Frankly I haven't seen DSM results very closely, but DSM can help
> us avoid full heap scans (and thats a big thing!), but it can't avoid the
> associated index scans and that might limit our ability to vacuum very
> large tables frequently.
I haven't seen DSM either so IMBFoS. You are right about index scans
though. Fortunately they are not as expensive as they used to be thanks
to Heikki's changes to allow physical order scanning.
--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
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