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Re: postgresql is slow with larger table even it is in RAM - Mailing list pgsql-performance

From Alvaro Herrera
Subject Re: postgresql is slow with larger table even it is in RAM
Date
Msg-id 20080325115921.GB6756@alvh.no-ip.org
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In response to postgresql is slow with larger table even it is in RAM  ("sathiya psql" <sathiya.psql@gmail.com>)
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sathiya psql escribió:

>     So now everything is in RAM, if i do a count(*) on this table it returns
> 327600 in 3 seconds, why it is taking 3 seconds ????? because am sure that
> no Disk I/O is happening.

It has to scan every page and examine visibility for every record.  Even
if there's no I/O involved, there's a lot of work to do.  I am not sure
if with your hardware it is expected for it to take 3 seconds though.
Do you see high CPU usage during that period?

--
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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