On 2020/06/29 18:53, Julien Rouhaud wrote:
On Mon, Jun 29, 2020 at 11:38 AM Fujii Masao
<masao.fu...@oss.nttdata.com> wrote:
Your benchmark result seems to suggest that the cause of the problem is
the contention of per-query spinlock in pgss_store(). Right?
This lock contention is likely to happen when multiple sessions run
the same queries.
One idea to reduce that lock contention is to separate per-query spinlock
into two; one is for planning, and the other is for execution. pgss_store()
determines which lock to use based on the given "kind" argument.
To make this idea work, also every pgss counters like shared_blks_hit
need to be separated into two, i.e., for planning and execution.
This can probably remove some overhead, but won't it eventually hit
the same issue when multiple connections try to plan the same query,
given the number of different queries and very low execution runtime?
Yes. But maybe we can expect that the idea would improve
the performance to the near same level as v12?
A POC patch should be easy to do and see how much it solves this
problem. However I'm not able to reproduce the issue, and IMHO unless
we specifically want to be able to distinguish planner-time counters
from execution-time counters, I'd prefer to disable track_planning by
default than going this way, so that users with a sane usage won't
have to suffer from a memory increase.
Agreed. +1 to change that default to off.
Regards,
--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION
