Re: Having query cache in core

On Mon, May 7, 2018 at 2:32 PM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:
> For interactive application only for one subset of queries the plan cache is
> interesting.
>
> @1 There are long queries - the planning time is not significant (although
> can be high), and then plan cache is not important
> @2 there are fast queries with fast planning time - usually we don't need
> plan cache too
> @3 there are fast queries with long planning time - and then plan cache is
> very interesting - can be difficult to separate this case from @1.

That's not my experience. I agree that plan caching isn't important
for long-running queries, but I think it *is* potentially important
for fast queries with fast planning time. Even when the planning time
is fast, it can be a significant percentage of the execution time.
Not long ago, we had a case at EDB where a customer was getting custom
plans instead of generic plans and that resulted in a significant
reduction in TPS.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company