On Mon, 22 Jul 2019 at 16:36, Tsunakawa, Takayuki
<tsunakawa.takay@jp.fujitsu.com> wrote:
>
> From: David Rowley [mailto:david.rowley@2ndquadrant.com]
> > For the use case we've been measuring with partitioned tables and the
> > generic plan generation causing a sudden spike in the number of
> > obtained locks, then having plan_cache_mode = force_custom_plan will
> > cause the lock table not to become bloated. I'm not sure there's
> > anything interesting to measure there.
>
> I meant the difference between the following two cases, where the query only touches one partition (e.g. SELECT ...
WHEREpkey = value):
>
> * plan_cache_mode=force_custom_plan: LocalLockHash won't bloat. The query execution time is steady.
>
> * plan_cache_mode=auto: LocalLockHash bloats on the sixth execution due to the creation of the generic plan. The
genericplan is not adopted because its cost is high. Later executions of the query will suffer from the bloat until
the1006th execution when LocalLockHash is shrunk.
I measured this again in
https://www.postgresql.org/message-id/CAKJS1f_ycJ-6QTKC70pZRYdwsAwUo+t0_CV0eXC=J-b5A2MegQ@mail.gmail.com
where I posted the v6 patch. It's the final results in the email. I
didn't measure plan_cache_mode = force_custom_plan. There'd be no lock
table bloat in that case and the additional overhead would just be
from the hash_get_num_entries() && hash_get_max_bucket() calls, which
the first results show next to no overhead for.
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services