Re: Fwd: Process scheduling in postgres

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От John R Pierce
Тема Re: Fwd: Process scheduling in postgres
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Msg-id 6e123c08-2b79-055f-efb4-1a6b6a0c1868@hogranch.com
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Ответ на Fwd: Process scheduling in postgres  (raghu vineel <raghuvineel@gmail.com>)
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On 4/22/2016 1:30 AM, raghu vineel wrote:

I have a 4 core CPU for postgres and I have submitted 6 queries parallely in 6 different sessions. But I am seeing only 1 query per CPU and the remainig queries are queued. I am not sure why is it happening. Do you have any special scheduler for postgres? I can see that CPU has been shared with other non postgres processes but postgres processes are not sharing any CPU within a core. The following is the process states.

lms       2868  2209 98 07:20 ?        00:02:30 postgres: lms controller [local] SELECT
lms       2869  2209 98 07:20 ?        00:02:30 postgres: lms controller [local] SELECT

lms       2870  2209  0 07:20 ?        00:00:00 postgres: lms controller [local] SELECT
lms       2871  2209  0 07:20 ?        00:00:00 postgres: lms controller [local] SELECT
lms       2872  2209  0 07:20 ?        00:00:00 postgres: lms controller [local] SELECT
lms       2873  2209 98 07:20 ?        00:02:30 postgres: lms controller [local] SELECT

If you see above, three Select queries have been queued. They are acquiring CPU only when there is a core without any postgres query running on it.

I know the postgres limitation of one query using only one core. But is there any limitation of one CPU running only one query at a time?

no such limitation.  any chance there's locking involved here?  take a look at pg_locks and pg_stat_activity the next time you run such a test.


-- 
john r pierce, recycling bits in santa cruz

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