Date: Sun, 12 Jan 2020 04:39:30 +0100
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Noah Misch <noah@leadboat.com>,
	Amit Khandekar <amitdkhan.pg@gmail.com>,
	Alvaro Herrera from 2ndQuadrant <alvherre@alvh.no-ip.org>,
	Andres Freund <andres@anarazel.de>,
	Juan =?utf-8?B?Sm9zw6kgU2FudGFtYXLDrWE=?= Flecha
 <juanjo.santamaria@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	Robert Haas <robertmhaas@gmail.com>,
	Thomas Munro <thomas.munro@gmail.com>
Subject: Re: logical decoding : exceeded maxAllocatedDescs for .spill files
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On Thu, Jan 09, 2020 at 07:40:12PM -0500, Tom Lane wrote:
>I wrote:
>>           ReorderBuffer: 223302560 total in 26995 blocks; 7056 free (3 chunks); 223295504 used
>
>> The test case is only inserting 50K fairly-short rows, so this seems
>> like an unreasonable amount of memory to be consuming for that; and
>> even if you think it's reasonable, it clearly isn't going to scale
>> to large production transactions.
>
>> Now, the good news is that v11 and later get through
>> 006_logical_decoding.pl just fine under the same restriction.
>> So we did something in v11 to fix this excessive memory consumption.
>> However, unless we're willing to back-port whatever that was, this
>> test case is clearly consuming excessive resources for the v10 branch.
>
>I dug around a little in the git history for backend/replication/logical/,
>and while I find several commit messages mentioning memory leaks and
>faulty spill logic, they all claim to have been back-patched as far
>as 9.4.
>
>It seems reasonably likely to me that this result is telling us about
>an actual bug, ie, faulty back-patching of one or more of those fixes
>into v10 and perhaps earlier branches.
>
>I don't know this code well enough to take point on looking for the
>problem, though.
>

Well, one thing we did in 11 is introduction of the Generation context.
In 10 we're still stashing all tuple data into the main AllocSet. I
wonder if backporting a4ccc1cef5a04cc054af83bc4582a045d5232cb3 and a
couple of follow-up fixes would make the issue go away.


regards

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