Re: Protocol forced to V2 in low-memory conditions?

On 2013-09-10 12:31:22 +0200, Magnus Hagander wrote:
> On Tue, Sep 10, 2013 at 5:29 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Maciek Sakrejda <m(dot)sakrejda(at)gmail(dot)com> writes:
> >> One of our customers seems to be running into exactly the issue
> >> hypothesized about by Tom here:
> >> http://www.postgresql.org/message-id/8040.1314403175@sss.pgh.pa.us
> >> Was the possibility of an inadvertent protocol downgrade addressed as part
> >> of that patch? I read through the thread, but it wasn't entirely clear.
> >
> > No, a quick look at report_fork_failure_to_client shows it still always
> > sends V2 protocol. We fixed some of the lesser issues discussed in that
> > thread, but I don't think we ever agreed how to deal with this one.
> >
> > I've been thinking of late that it might be time to retire libpq's
> > support for V2 protocol (other than in the specific context of the first
> > error message received while trying to make a connection). If we did
> > that, we'd remove the code path that thinks it should downgrade to V2
> > protocol, and thus fix this problem by removing code not adding more.
> >
> > However, that doesn't sound like a back-patchable solution, and also
> > it remains unclear whether non-libpq clients such as JDBC have an issue
> > with this.
>
> It's probably worth polling for that. I believe the jdbc driver at
> least has code for it, but I don't know if it's a requirement at this
> point.

Yes, it has code for it and I think it's still used pretty frequently to
circumvent prepared statement planning problems (misestimation,
indeterminate types). So I think we need convincing reasons to break
their usage.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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