| From: | Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> |
|---|---|
| To: | "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com>, "Imai, Yoshikazu" <imai(dot)yoshikazu(at)jp(dot)fujitsu(dot)com> |
| Cc: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: speeding up planning with partitions |
| Date: | 2019-01-18 05:28:32 |
| Message-ID: | 5b76aea7-2785-f3d0-4184-3039eddab8ba@lab.ntt.co.jp |
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| Lists: | pgsql-hackers |
Tsunakawa-san,
On 2019/01/18 14:12, Tsunakawa, Takayuki wrote:
> From: Amit Langote [mailto:Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp]
>> Are you saying that, when using auto mode, all executions of the query
>> starting from 7th are slower than the first 5 executions? That is, the
>> latency of creating and using a custom plan increases *after* a generic
>> plan is created and discarded on the 6th execution of the query? If so,
>> that is inexplicable to me.
>
> Isn't CheckCachedPlan() (and AcquireExecutorLocks() therein) called in every EXECUTE after 6th one due to some unknow issue?
CheckCachedPlan is only called if choose_custom_plan() returns false
resulting in generic plan being created/reused. With plan_cache_mode =
auto, I see it always returns true, because a custom plan containing a
single partition to scan is way cheaper than the generic plan.
> Does choose_custom_plan() always return true after 6th EXECUTE?
Yes.
Thanks,
Amit
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