Re: dsa_allocate() faliure

On Thu, Aug 16, 2018 at 8:32 AM, Sand Stone <sand.m.stone@gmail.com> wrote:
> Just as a follow up. I tried the parallel execution again (in a stress
> test environment). Now the crash seems gone. I will keep an eye on
> this for the next few weeks.

Thanks for the report.  That's great news, but it'd be good to
understand why it was happening.

> My theory is that the Citus cluster created and shut down a lot of TCP
> connections between coordinator and workers. If running on untuned
> Linux machines, the TCP ports might run out.

I'm not sure how that's relevant, unless perhaps it causes executor
nodes to be invoked in a strange sequence that commit fd7c0fa7 didn't
fix?  I wonder if there could be something different about the control
flow with custom scans, or something about the way Citus worker nodes
invoke plan fragments, or some error path that I failed to consider...
It's a clue that all of your worker nodes reliably crashed at the same
time on the same/similar queries (presumably distributed query
fragments for different shards), making it seem more like a
common-or-garden bug rather than some kind of timing-based heisenbug.
If you ever manage to reproduce it, an explain plan and a back trace
would be very useful.

> Of course, I am using "newer" PG10 bits and Citus7.5 this time.

Hmm.  There weren't any relevant commits to REL_10_STABLE that I can
think of.  And (with the proviso that I know next to nothing about
Citus) I just cloned https://github.com/citusdata/citus.git and
skimmed through "git diff origin/release-7.4..origin/release-7.5", and
nothing is jumping out at me.  Can you still see the problem with
Citus 7.4?

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