Subject: Re: logical decoding / rewrite map vs. maxAllocatedDescs
To: Andres Freund <andres@anarazel.de>,
 Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
References: <bc07e92b-d3b9-fabc-2993-edc0ef89be67@2ndquadrant.com>
 <20180813144630.hmzdrbviwao64ube@alvherre.pgsql>
 <20180813144946.fn4zpdwpucx43emz@alap3.anarazel.de>
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <f8221cf4-719c-ac4e-56bf-3be106c41d92@2ndquadrant.com>
Date: Tue, 14 Aug 2018 13:49:03 +0200
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On 08/13/2018 04:49 PM, Andres Freund wrote:
> Hi,
> 
> On 2018-08-13 11:46:30 -0300, Alvaro Herrera wrote:
>> On 2018-Aug-11, Tomas Vondra wrote:
>>
>>> Hmmm, it's difficult to compare "bt full" output, but my backtraces look
>>> somewhat different (and all the backtraces I'm seeing are 100% exactly
>>> the same). Attached for comparison.
>>
>> Hmm, looks similar enough to me -- at the bottom you have the executor
>> doing its thing, then an AcceptInvalidationMessages in the middle
>> section atop which sit a few more catalog accesses, and further up from
>> that you have another AcceptInvalidationMessages with more catalog
>> accesses.  AFAICS that's pretty much the same thing Andres was
>> describing.
> 
> It's somewhat different because it doesn't seem to involve a reload of a
> nailed table, which my traces did.  I wasn't able to reproduce the crash
> more than once, so I'm not at all sure how to properly verify the issue.
> I'd appreciate if Thomas could try to do so again with the small patch I
> provided.
> 

I'll try in the evening. I've tried reproducing it on my laptop, but I 
can't make that happen for some reason - I know I've seen some crashes 
here, but all the reproducers were from the workstation I have at home.

I wonder if there's some subtle difference between the two boxes, making 
it more likely on one of them ... the whole environment (distribution, 
packages, compiler, ...) should be exactly the same, though. The only 
thing I can think of is different CPU speed, possibly making some race 
conditions more/less likely. No idea.

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services