Perhaps a bunch of processes waiting on the access exclusive
lock on
the materialized view being released?
log_lock_waits might help you if the MV takes more than a
second to
refresh, otherwise, you might need to have a look at
ungranted locks
in pg_locks and see if the number of locks spikes during the
refresh.
I think David's got the right idea here. Like he said,
investigate pg_locks, if it is the refresh materialized
view, you can avoid the problem by doing 'REFRESH
MATERIALIZED VIEW CONCURRENTLY'. You will need at least one
unique index on the table.
