Re: PQcancel may hang in the recv call

Peter Juhasz <pjuhasz(at)uhusystems(dot)com> writes:
> We've found a situation where canceling a query may cause the client to
> hang, possibly indefinitely. This can happen if the network connection
> fails in a specific way.
> ...
> However, if the network fails in a way that the connection appears to
> have been established but subsequent packages are dropped silently,
> this recv() call will block.

Hmm. I would expect the recv to eventually fail based on TCP timeouts,
but I agree that that would be much longer than you'd typically wish
to wait.

> Is this known?

I do not recall anyone ever reporting something similar --- and that code
has been like that for a long time.

> Is this a bug?

I wouldn't call it that exactly. There might be an opportunity for
improvement here, but it's not very clear what. Just introducing a
timeout would likely create more problems than it fixes, considering the
evident rarity of the problem. The race condition hazard that the recv()
is trying to prevent is definitely real: we used to not have that, and
we got bug reports, cf
http://www.postgresql.org/message-id/flat/20030915070801(dot)GD23844(at)opencloud(dot)com

regards, tom lane