Re: BUG #17974: Walsenders memory usage suddenly spike to 80G+ causing OOM and server reboot

On Wed, Jun 14, 2023 at 12:05:32AM +0000, PG Bug reporting form wrote:
> We are running relatively large and busy Postgres database on RDS and using
> logical replication extensively. We currently have 7 walsenders and while we
> often see replication falls behind due to high transactional volume, we've
> never experienced memory issues in 14.6 and below. After recent upgrade to
> 14.8, we already had several incidents where walsender processes RES memory
> would suddenly increase to over 80GB each causing freeable memory on the
> instance to go down to zero. Interesting that even after Instance reboot,
> the memory used by walsender processes won't get released until we restart
> the replication and drop the logical slots. The logical_decoding_work_mem
> was set to 512MB in time of the last incident but we recently lowered it to
> 128MB.
>
> Any known issues in pg 14.8 that would trigger this behaviour?

Yes, there are known issues with memory handling in logical
replication setups.  See for example this thread:
https://www.postgresql.org/message-id/CAMnUB3oYugXCBLSkih+qNsWQPciEwos6g_AMbnz_peNoxfHwyw@mail.gmail.com

This is not a simple problem, unfortunately :/
--
Michael