Tatsuo Ishii <t-ishii@sra.co.jp> writes:
> Strange enough, there's no other backend (of course except stats
> collectors) here. I make sure this with ps and pg_stat_activity view.
If you have no better way of determining what's going on, it might help
to recompile with LOCK_DEBUG defined, then enable trace_lwlocks in
postgresql.conf (better turn on debug_print_query, log_timestamp, and
log_pid too). This will generate rather voluminous log output, perhaps
enough to provide a clue.
regards, tom lane