Re: speeding up planning with partitions

Tsunakawa-san,

On 2019/01/18 14:12, Tsunakawa, Takayuki wrote:
> From: Amit Langote [mailto:Langote_Amit_f8@lab.ntt.co.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