Detecting loss of client connection (was Re: Bug in walsender when calling out to do_pg_stop_backup (and others?))

Thinking about this some more, why don't we just elog(FATAL) in
internal_flush(), if the write fails, instead of setting the flag and
waiting for the next CHECK_FOR_INTERRUPTS(). That sounds scary at first,
but why not?

There's this comment in internal_flush():

> /*
> * Careful: an ereport() that tries to write to the client would
> * cause recursion to here, leading to stack overflow and core
> * dump! This message must go *only* to the postmaster log.

That's understandable.

> * If a client disconnects while we're in the midst of output, we
> * might write quite a bit of data before we get to a safe query
> * abort point. So, suppress duplicate log messages.

But what about this? Tracing back the callers, I don't see any that
would be upset if we just threw an error there. One scary aspect is if
you're within a critical section, but I don't think we currently send
any messages while in a critical section. And we could refrain from
throwing the error if we're in a critical section, to be safe.

> */
> if (errno != last_reported_send_errno)
> {
> last_reported_send_errno = errno;
> ereport(COMMERROR,
> (errcode_for_socket_access(),
> errmsg("could not send data to client: %m")));
> }

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com