Re: MultiXactMemberControlLock contention on a replica

> On Feb 15, 2021, at 08:15, Laurenz Albe <laurenz.albe@cybertec.at> wrote:
> Right.  I cannot think of any other reason, given that the standby only
> allows reading.  It's just an "xmax", and PostgreSQL needs to read the
> multixact to figure out if it can see the row or not.

OK, I think I see the scenario: A very large number of sessions on the primary all touch or create rows which refer to
aparticular row in another table by foreign key, but they don't modify that row.  A lot of sessions on the secondary
allread the row in the referred-to table, so it has to get all the members of the multixact, and if the multixact
structurehas spilled to disk, that gets very expensive. 

--
-- Christophe Pettus
   xof@thebuild.com