> On Feb 15, 2021, at 08:15, Laurenz Albe <laurenz.a...@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 a particular row in another table by
foreign key, but they don't modify that row. A lot of sessions on the
secondary all read the row in the referred-to table, so it has to get all the
members of the multixact, and if the multixact structure has spilled to disk,
that gets very expensive.
--
-- Christophe Pettus
x...@thebuild.com
