Re: BUG #18141: sorry, too many clients error occurring very frequently

Joe Conway <mail@joeconway.com> writes:
> Maybe, maybe not. I have seen two other cases that are similar. One was 
> an upgrade from 12.8 to 12.12 and the other an upgrade from 13.4 to 13.8.

> I checked and 12.8 was stamped is the same date as 13.4, and 12.12 the 
> same day as 13.8.

> In both cases queries against pg_stat_statements suddenly started taking 
> more memory leading to spillage to pg_temp and a step degradation in 
> overall performance. In at least one of those cases the 
> solution/workaround was to increase work_mem. In the other I think 
> pg_stat_statements was disabled.

> Myself and at least one other hacker looked at the pg_stat_statements 
> specific changes in that time interval and saw no smoking gun.

> But it is possible that something else backpatched to both branches 
> between Aug 09, 2021 and Aug 8, 2022 has caused a more general 
> performance regression which we have yet to track down.

Hmm.  My first instinct is to wonder about changes in plan selection.
How complex were the troublesome queries?

            regards, tom lane