Re: pg_reset_stats + cache I/O %

Out of curiosity, why do you want this info? More important, do the
folks who are looking at this understand that a key part of PostgreSQL's
tuning strategy is to let the OS handle the bulk of the caching?

On Wed, Mar 08, 2006 at 08:59:51AM -0500, mcelroy, tim wrote:
> Thanks Tom, sorry I neglected to copy the list on my previous email.....
>
> Does this query make sense and is it valid for an accurate cache % hit ratio
> for the entire DB? I would assume I could use the same logic with other
> views such as pg_stat_user_tables to get a per table ratio?
>
> SELECT 100 - round((blks_hit::numeric / (blks_hit::numeric +
> blks_read::numeric)) * 100,2)
> AS "Cache % Hit"
> FROM pg_stat_database
> WHERE datname = 'Fix1';
>
> <RETURNS>
>
> Cache % Hit
> --------------------
> 98.06
> (1 row)
>
> Thank you,
> Tim
>
> -----Original Message-----
> From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
> Sent: Tuesday, March 07, 2006 2:37 PM
> To: mcelroy, tim
> Cc: 'pgsql-performance(at)postgresql(dot)org'
> Subject: Re: [PERFORM] pg_reset_stats + cache I/O %
>
> "mcelroy, tim" <tim(dot)mcelroy(at)bostonstock(dot)com> writes:
> > ERROR: function round(double precision, integer) does not exist
>
> Try coercing to numeric instead of float. Also, it'd be a good idea to
> put that coercion outside the sum()'s instead of inside --- summing
> bigints is probably noticeably faster than summing numerics.
>
> regards, tom lane

--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
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