Re: Logical replication - ERROR: could not send data to WAL stream: cannot allocate memory for input buffer

On Fri, Jun 05, 2020 at 10:57:46PM +0200, Aleš Zelený wrote:
> we are using logical replication for more than 2 years and today I've found
> new not yet know error message from wal receiver. The replication was in
> catchup mode (on publisher side some new tables were created and added to
> publication, on subscriber side they were missing).

This comes from pqCheckInBufferSpace() in libpq when realloc() fails,
most probably because this host ran out of memory.

> Repeated several times, finally it proceeded and switch into streaming
> state. The OS has 64GB RAM, OS + database instance are using usually 20GB
> rest is used as OS buffers. I've checked monitoring (sampled every 10
> seconds) and no memory usage peak was visible, so unless it was a very
> short memory usage peak, I'd not expect the system running out of memory.
>
> Is there something I can do to diagnose and avoid this issue?

Does the memory usage increase slowly over time? Perhaps it was not a
peak and the memory usage was not steady? One thing that could always
be tried if you are able to get a rather reproducible case would be to
use valgrind and check if it is able to detect any leaks. And I am
afraid that it is hard to act on this report without more information.
--
Michael