| From: | Joe Conway <mail(at)joeconway(dot)com> |
|---|---|
| To: | mladen(dot)gogala(at)vmsinfo(dot)com |
| Cc: | Neil Whelchel <neil(dot)whelchel(at)gmail(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Slow count(*) again... |
| Date: | 2010-10-10 02:10:38 |
| Message-ID: | 4CB1209E.9000706@joeconway.com |
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| Lists: | pgsql-hackers pgsql-performance |
On 10/09/2010 06:54 PM, Mladen Gogala wrote:
> In another database, whose name I will not mention, there is a parameter
> db_file_multiblock_read_count which specifies how many blocks will be
> read by a single read when doing a full table scan. PostgreSQL is in
> dire need of something similar and it wouldn't even be that hard to
> implement.
You're correct in that it isn't particularly difficult to implement for
sequential scans. But I have done some testing with aggressive read
ahead, and although it is clearly a big win with a single client, the
benefit was less clear as concurrency was increased.
Joe
--
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