> On Feb 15, 2021, at 08:15, Laurenz Albe <laurenz.albe@xxxxxxxxxxx> 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 xof@xxxxxxxxxxxx
