Le mardi 27 février 2007 15:00, George Nychis a écrit :
> Hey all,
>
> So I have a master table called "flows" and 400 partitions in the format
> "flow_*" where * is equal to some epoch.
>
> Each partition contains ~700,000 rows and has a check such that 1 field is
> equal to a value:
> "flows_1107246900_interval_check" CHECK ("interval" = '2005-02-01
> 03:35:00'::timestamp without time zone)
>
> Each partition has a different and unique non-overlapping check.
>
> This query takes about 5 seconds to execute:
> dp=> select count(*) from flows_1107246900;
> count
> --------
> 696836
> (1 row)
>
> This query has been running for 10 minutes now and hasn't stopped:
> dp=> select count(*) from flows where interval='2005-02-01 03:35:00';
>
> Isn't partitioning supposed to make the second query almost as fast? My
> WHERE is exactly the partitioning constraint, therefore it only needs to go
> to 1 partition and execute the query.
>
> Why would it take magnitudes longer to run? Am i misunderstanding
> something?
perhaps you should consider constraint_exclusion
http://www.postgresql.org/docs/current/static/ddl-partitioning.html
http://www.postgresql.org/docs/current/static/runtime-config-query.html#GUC-CONSTRAINT-EXCLUSION
>
> Thanks!
> George
>
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