Horton

Re: logical decoding : exceeded maxAllocatedDescs for .spill files

Tomas Vondra <tomas.vondra@2ndquadrant.com>

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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 José Santamaría Flecha <juanjo.santamaria@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Robert Haas <robertmhaas@gmail.com>, Thomas Munro <thomas.munro@gmail.com>
Date: 2020-01-12T03:39:30Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. When a TAP file has non-zero exit status, retain temporary directories.

  2. Fix running out of file descriptors for spill files.

  3. Track statistics for spilling of changes from ReorderBuffer.

  4. Handle ReadFile() EOF correctly on Windows.

  5. Add logical_decoding_work_mem to limit ReorderBuffer memory usage.

  6. Generational memory allocator

  7. Support retaining data dirs on successful TAP tests

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
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