Re: Unexplained rapid growth in memory usage of idle backends

> On 13/05/2023 00:12 CEST Alex Balashov <abalashov(at)evaristesys(dot)com> wrote:
>
> We have an application that has a preforked worker pool architecture and
> opens a relatively large (70+) number of persistent connections to PostgreSQL
> 14, and have `max_connections` set to 200 accordingly.

Which pg14 minor version exactly?

> Occasionally, about once every 2 months, we'll get a slow-motion implosion
> over a period of about 24 hours, where the resident memory size of some of
> the backends shoots up from a reasonable few hundred MB to several gigs --
> and will keep growing, e.g.
>
> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
> 3932733 postgres 20 0 637740 327124 323840 R 10.7 0.5 0:00.11 postgres
> 782930 postgres 20 0 3151360 2.8g 551704 S 9.7 4.5 221:43.17 postgres
> 782839 postgres 20 0 2999896 2.7g 551832 S 8.7 4.3 220:54.55 postgres
> 3932734 postgres 20 0 636128 338168 336096 R 8.7 0.5 0:00.09 postgres
> 3932735 postgres 20 0 636128 319824 317768 R 8.7 0.5 0:00.09 postgres
> 782851 postgres 20 0 3142152 2.8g 551872 S 7.8 4.5 221:22.62 postgres
> 782855 postgres 20 0 3155144 2.8g 551828 S 7.8 4.5 221:38.59 postgres
> 782897 postgres 20 0 3148808 2.8g 551724 S 7.8 4.5 220:05.94 postgres
> 783106 postgres 20 0 3152416 2.8g 551912 S 7.8 4.5 221:24.40 postgres
> 783168 postgres 20 0 2992592 2.7g 551968 S 7.8 4.2 220:36.06 postgres
> 782843 postgres 20 0 3146772 2.8g 551944 R 4.9 4.5 221:38.46 postgres
> 782778 postgres 20 0 3150956 2.8g 551852 R 3.9 4.5 220:49.88 postgres

Function pg_log_backend_memory_contexts(pid int) may give you some insights on
on the memory allocation for specific backends.

https://www.postgresql.org/docs/14/functions-admin.html#FUNCTIONS-ADMIN-SIGNAL-TABLE

--
Erik