PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
> 9. VACUUM is not working, even after upgrades vacuum is not working. If I
> unset archive_mode = on, wal_level = replica and leave to default, vacuum
> not working. Following is the message I get, no dead rows removed, but lot
> of delete/update has happeded to the table.
There are basically two possibilities here:
1. You have an old open transaction somewhere. Possibly an
uncommitted two-phase transaction. The pg_prepared_xacts view
would help identify the latter.
2. You have a replication slot that's holding back global xmin.
Look in pg_replication_slots.
regards, tom lane