Re: performance of partitioning?

cedric wrote:
> 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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>

That sounds like what i'm looking for, thanks.  I'll give it a try and report back.

- George