Re: PG 11.8 > PG 12.3 : Unable to allocate section memory

"JOIGNY Michael @Neteven" <mjoigny(at)neteven(dot)com> writes:
> We have migrated from postgresql 11.8 to 12.3,unfortunately we have
> sometimes the following errors in the logs, causing postgres process to
> be killed.
> 2020-08-12 14:20:29.043 CEST [134644]: [71-1]
> user=xx,db=xx,app=[unknown],client=localhost FATAL:  out of memory
> 2020-08-12 14:20:29.049 CEST [30022]: [6126-1]
> user=xx,db=xx,app=[unknown],client=localhost FATAL:  fatal llvm error:
> Unable to allocate section memory!

Hmm, seems like your system is under undue memory pressure ...

> max_connections = 3600

This seems slightly insane. Get a pooler ... or, since you say you
already have one, let *it* do the multiplexing.

> Note that we had the same configuration under PG11 without any problem.

One thing that you might not have noticed is that "jit" defaults to on
as of v12. Turning it off would prevent this specific crash case.
(The fact that it's a crash comes from llvm's crummy error handling :-()
You might still have OOM problems, but with luck they'd not take down
the whole database.

regards, tom lane