Re: Cancel race condition

Shay Rojansky <roji@roji.org> writes:
> My questions/comments:
>    - Does PostgreSQL *guarantee* that once the connection used to send the
>    cancellation request is closed by the server, the cancellation has been
>    delivered (as mentioned by Tom)? In other words, should I be designing a
>    .NET driver around this behavior?

The signal's been *sent*.  Whether it's been *delivered* is something
you'd have to ask your local kernel hacker.  The POSIX standard appears
to specifically disclaim any such guarantee; in fact, it doesn't even
entirely promise that a self-signal is synchronous.  There are also
issues like what if the target process currently has signals blocked;
does "delivery" mean that the signal handler's been entered, or something
weaker?

In any case, Postgres has always considered that query cancel is a "best
effort" thing, so even if I thought this was 100% portably reliable,
I would not be in favor of promising anything in the docs.
        regards, tom lane