Re: dsa_allocate() faliure

On Mon, Feb 11, 2019 at 11:02 AM Justin Pryzby <pryzby@telsasoft.com> wrote:
> On Mon, Feb 11, 2019 at 09:45:07AM +1100, Thomas Munro wrote:
> > Ouch.  Yeah, that'd do it and matches the evidence.  With this change,
> > I couldn't reproduce the problem after 90 minutes with a test case
> > that otherwise hits it within a couple of minutes.
> ...
> > Note that this patch addresses the error "dsa_allocate could not find
> > %zu free pages".  (The error "dsa_area could not attach to segment" is
> > something else and apparently rarer.)
>
> "could not attach" is the error reported early this morning while
> stress-testing this patch with queued_alters queries in loops, so that's
> consistent with your understanding.  And I guess it preceded getting stuck on
> lock; although I don't how long between the first happened and the second, I'm
> guess not long and perhaps immedidately; since the rest of the processes were
> all stuck as in bug#15585 rather than ERRORing once every few minutes.
>
> I mentioned that "could not attach to segment" occurs in leader either/or
> parallel worker.  And most of the time causes an ERROR only, and doesn't wedge
> all future parallel workers.  Maybe bug#15585 "wedged" state maybe only occurs
> after some pattern of leader+worker failures (?)  I've just triggered bug#15585
> again, but if there's a pattern, I don't see it.
>
> Please let me know whether you're able to reproduce the "not attach" bug using
> simultaneous loops around the queued_alters query; it's easy here.

I haven't ever managed to reproduce that one yet.  It's great you have
a reliable repro...  Let's discuss it on the #15585 thread.

-- 
Thomas Munro
http://www.enterprisedb.com