Re: Wait free LW_SHARED acquisition - v0.2

On 2014-11-17 10:21:04 -0500, Robert Haas wrote:
> Andres, where are we with this patch?
>
> 1. You're going to commit it, but haven't gotten around to it yet.
>
> 2. You're going to modify it some more and repost, but haven't gotten
> around to it yet.
>
> 3. You're willing to see it modified if somebody else does the work,
> but are out of time to spend on it yourself.
>
> 4. Something else?

I'm working on it. Amit had found a hang on PPC that I couldn't
reproduce on x86. Since then I've reproduced it and I think yesterday I
found the problem. Unfortunately it always took a couple hours to
trigger...

I've also made some, in my opinion, cleanups to the patch since
then. Those have the nice side effect of making the size of struct
LWLock smaller, but that wasn't actually the indended effect.

I'll repost once I've verified the problem is fixed and I've updated all
commentary.

The current problem is that I seem to have found a problem that's also
reproducible with master :(. After a couple of hours a
pgbench -h /tmp -p 5440 scale3000 -M prepared -P 5 -c 180 -j 60 -T 20000 -S
against a
-c max_connections=200 -c shared_buffers=4GB
cluster seems to hang on PPC. With all the backends waiting in buffer
mapping locks. I'm now making sure it's really master and not my patch
causing the problem - it's just not trivial with 180 processes involved.

Greetings,

Andres Freund

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