Re: pg_dump versus hash partitioning

On Fri, Mar 10, 2023 at 10:10:14PM -0500, Tom Lane wrote:
> Julien Rouhaud  writes:
> > Working on some side project that can cause dump of hash partitions to be
> > routed to a different partition, I realized that --load-via-partition-root can
> > indeed cause deadlock in such case without FK dependency or anything else.
>
> > The problem is that each worker will perform a TRUNCATE TABLE ONLY followed by
> > a copy of the original partition's data in a transaction, and that obviously
> > will lead to deadlock if the original and locked partition and the restored
> > partition are different.
>
> Oh, interesting.  I wonder if we can rearrange things to avoid that.

The BEGIN + TRUNCATE is only there to avoid generating WAL records just in case
the wal_level is minimal.  I don't remember if that optimization still exists,
but if yes we could avoid doing that if the server's wal_level is replica or
higher?  That's not perfect but it would help in many cases.