Re: pg_terminate_backend for same-role

On Thu, Mar 15, 2012 at 04:14:03PM -0700, Daniel Farina wrote:
> Parallel to pg_cancel_backend, it'd be nice to allow the user to just
> outright kill a backend that they own (politely, with a SIGTERM),
> aborting any transactions in progress, including the idle transaction,
> and closing the socket.

+1

> I imagine the problem is a race condition whereby a pid might be
> reused by another process owned by another user (doesn't that also
> affect pg_cancel_backend?). Shall we just do everything using the
> MyCancelKey (which I think could just be called "SessionKey",
> "SessionSecret", or even just "Session") as to ensure we have no case
> of mistaken identity? Or does that end up being problematic?

No, I think the hazard you identify here is orthogonal to the question of when
to authorize pg_terminate_backend(). As you note downthread, protocol-level
cancellations available in released versions already exhibit this hazard. I
wouldn't mind a clean fix for this, but it's an independent subject.

Here I discussed a hazard specific to allowing pg_terminate_backend():
http://archives.postgresql.org/message-id/20110602045955.GC8246@tornado.gateway.2wire.net

To summarize, user code can trap SIGINT cancellations, but it cannot trap
SIGTERM terminations. If a backend is executing a SECURITY DEFINER function
when another backend of the same role calls pg_terminate_backend() thereon,
the pg_terminate_backend() caller could achieve something he cannot achieve in
PostgreSQL 9.1. I vote that this is an acceptable loss.

Thanks,
nm