Re: High CPU usage after partitioning

On Tue, Jan 22, 2013 at 3:46 PM, Andrew Dunstan <andrew(at)dunslane(dot)net> wrote:

> The query is pretty simple and standard, the behaviour (and the plan) is
> totally different when it comes to a partitioned table.
>
>>
>> Partioned table query => explain analyze SELECT "sb_logs".* FROM
>> "sb_logs" WHERE (device_id = 901 AND date_taken = (SELECT MAX(date_taken)
>> FROM sb_logs WHERE device_id = 901));
>>
>>
> And there you have it. Constraint exclusion does not work in cases like
> this. It only works with static expressions (such as a literal date in this
> case).

Ok, but I would have expected same plant repeated 4 times. When the table
is not partitioned, the plan is defintely smarter: it knows that index is
reversed and looks for max with an index scan backward). When the table is
partitioned, it scan forward and I guess it will always do a full index
scan.

--
rd

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