It's not entirely clear what your question is, but here are some possible answers:
1. For quite some time now, the "query" column in pg_stat_activity has been defined as "the query currently or most recently run by the session"; it's intentional that it doesn't go back to "<idle>" anymore. You need to look at the "state" column to tell whether the session is actively running the query or not.
2. Are you sure that operating system user "crest" isn't connecting as database user "postgres"?
Yes.
3. pg_cancel_backend() is only supposed to terminate the current query (if any), not kill the session. If you want the latter try pg_terminate_backend().
Thanks. I was under the wrong impression that pg_cancel_backend() will do both.
