Re: Example code Re: Singleton SELECT inside cursor loop

On 10/1/22 07:21, Christoph Moench-Tegeder wrote:
> ## Ron (ronljohnsonjr(at)gmail(dot)com):
>
>> 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!

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