On 10/1/22 07:21, Christoph Moench-Tegeder wrote:
## Ron (ronljohnsonjr@xxxxxxxxx):
Note how quickly it runs the first five times, but takes 780x longer the
sixth time I run it. Exiting psql and entering again causes the same
slowness the sixth time it's run.
Tanks at the sixth time? That rings a bell: "The current rule for this
is that the first five executions are done with custom plans[...]" from
https://www.postgresql.org/docs/12/sql-prepare.html
The question then is "why am I just now seeing the problem?" We've been
using v12 for two years, and it just happened.
The only recent change is that I upgraded it from RDS 12.10 to 12.11 a
couple of weeks ago.
And your functions create prepared statements under the hood:
https://www.postgresql.org/docs/12/plpgsql-implementation.html#PLPGSQL-PLAN-CACHING
The same thing happens when I put the SELECT in a prepared statement, so
that seems the likely cause.
I guess you should visit
https://www.postgresql.org/docs/12/runtime-config-query.html#GUC-PLAN-CACHE_MODE
and try if plan_cache_mode = force_custom_plan helps here.
That solved the problem. Thank you!
--
Angular momentum makes the world go 'round.
