From: | Rod Taylor <pg(at)rbt(dot)ca> |
---|---|
To: | Valerie Schneider DSI/DEV <Valerie(dot)Schneider(at)meteo(dot)fr> |
Cc: | Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au>, Postgresql Performance <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: [GENERAL] Tuning queries on large database |
Date: | 2004-08-05 13:18:47 |
Message-ID: | 1091711927.84496.22.camel@jester |
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Thread: | |
Lists: | pgsql-performance |
> so it takes about 28 Gb instead of 68 Gb !
Huzzah!
> For my different queries, it's better but less performant than oracle :
Not surprising. Oracle has a number of optimizations that we don't have
implemented at this point, particularly where aggregates are involved.
One that PG could use, particularly for Q4, is the ability to execute a
selective sequential scan based on a read of the index -- right now it
pulls in actual data from the table structure while following the index
-- creates unnecessary disk-head movement.
The only solution to that, at the moment, is to cluster the table by
pk_data.
I am curious though, could you run the below query on both systems and
report back times?
select 'Q4', * from data where num_poste between 600 and 625;
I'm wondering if Oracle is using a shortcut since the count(*) doesn't
actually require the data -- just knowledge of whether a matching row
exists or not.
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