Re: Debugging leaking memory in Postgresql 13.2/Postgis 3.1

Hello Tom,

On 31.03.2021 20:24, Tom Lane wrote:
> Based on nearby threads, it occurs to me to ask whether you have JIT
> enabled, and if so whether turning it off helps.  There seems to be
> a known leak of the code fragments generated by that in some cases.

That's it!

I am quite surprised that a functionality, which is on by default does 
generate such a massive leak and goes sort of undetected.

A single backend was leaking 250MB/hour, with my multiple connections it 
was 2GB. But exactly that happened.

Doing a set jit=off immediately stopped the leak.


You mentioned that this seems to be known. Do you have pointers to the 
relevant bug-tracker/thread? I would like to follow up on this.

I have not measured the impact of jit, but in theory it could bring 
larger performance benefits. So having it enabled sounds like a good 
idea, once it stops leaking.


I tried running Valgrind on postgres but I had not much success with it. 
processes seemed to terminate quite frequently. My last use of Valgrind 
is a while ago and my use-case back then was probably much simpler.

Is it known which queries are leading to a leak? I still have the 
recording of mine, including explain. Would it help to narrow it further 
down to single queries which leak? Or is the JIT re-creating optimized 
code for each slightly modified one without freeing the old ones? So 
re-running the same query would not leak?

https://downloads.osm-tools.org/postgresql-2021-04-03_183913.csv.gz


Stephan