Re: How to find if a SELECT is reading from buffer or disk ?

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От Chirag Dave
Тема Re: How to find if a SELECT is reading from buffer or disk ?
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Msg-id AANLkTimaCOhP9WDm8Dxuu2rBWLOvxksLjFPlFjEb_4uG@mail.gmail.com
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Ответ на How to find if a SELECT is reading from buffer or disk ?  (Balkrishna Sharma <b_ki@hotmail.com>)
Ответы Re: How to find if a SELECT is reading from buffer or disk ?  (Cédric Villemain <cedric.villemain.debian@gmail.com>)
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On Tue, May 25, 2010 at 1:48 PM, Balkrishna Sharma <b_ki@hotmail.com> wrote:
Hi,

I am increasing the shared_buffer size in postgresql.conf and want to measure its effect on READ. In essence I want to know if the SELECT queries I am firing repeatedly is reading from the buffer or going directly to the disk.

I am expecting the first SELECT to go to disk and the subsequent call of the same SELECT to read from buffer .

Right now I am just looking at execution time of the SELECTs and trying to conclude. But there should be a direct way to see where the SELECT reads from.

You can also use pg_stat_database view. you can compute cache reads percentage of the total number of reads (cache and physical) between the two snapshots using  pg_stat_database.blks_hit  and pg_stat_database.blks_read.

Chirag Dave  416-673-4102
Database Administrator, Afilias Canada Corp.
cdave@ca.afilias.info




How can I accomplish this ?

Thanks
Bala

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