Dominique Devienne <ddevienne@gmail.com> writes:
> So when and how fast does pg_stat_activity update, in the face of a
> PQfinish?
The shared state underlying pg_stat_activity is updated
immediately when something changes. However ...
PQfinish is asynchronous: it sends a "goodbye" message and then
closes the connection without waiting for a response. So
depending on system load, the associated backend could still be
alive for some milliseconds. There might be other client
libraries that do that differently.
Another thing that might be biting you is that a backend inspecting
pg_stat_activity() takes a snapshot of the view's contents and then
holds onto that snapshot until end of transaction. You can get
around that with pg_stat_clear_snapshot().
regards, tom lane
