Re: High CPU usage after partitioning
| От | rudi |
|---|---|
| Тема | Re: High CPU usage after partitioning |
| Дата | |
| Msg-id | CAMxPiKEFHXnrpcfq6DxjAyrMXPMNUndtbxp+SouzfE3-LMZBwA@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: High CPU usage after partitioning (Andrew Dunstan <andrew@dunslane.net>) |
| Ответы |
Re: High CPU usage after partitioning
|
| Список | pgsql-performance |
On Tue, Jan 22, 2013 at 3:46 PM, Andrew Dunstan <andrew@dunslane.net> wrote:
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rd
This is the way the world ends.
Not with a bang, but a whimper.
The query is pretty simple and standard, the behaviour (and the plan) is totally different when it comes to a partitioned table.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).
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));
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
This is the way the world ends.
Not with a bang, but a whimper.
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