On 11/05/17 16:33, Stas Kelvich wrote:
> 
>> On 10 May 2017, at 11:43, Petr Jelinek <petr.jeli...@2ndquadrant.com> wrote:
>>
>> On 09/05/17 22:11, Erik Rijkers wrote:
>>> On 2017-05-09 21:00, Petr Jelinek wrote:
>>>> On 09/05/17 19:54, Erik Rijkers wrote:
>>>>> On 2017-05-09 11:50, Petr Jelinek wrote:
>>>>>
>>>>
>>>> Ah okay, so this is same issue that's reported by both Masahiko Sawada
>>>> [1] and Jeff Janes [2].
>>>>
>>>> [1]
>>>> https://www.postgresql.org/message-id/CAD21AoBYpyqTSw%2B%3DES%2BxXtRGMPKh%3DpKiqjNxZKnNUae0pSt9bg%40mail.gmail.com
>>>>
>>>> [2]
>>>> https://www.postgresql.org/message-id/flat/CAMkU%3D1xUJKs%3D2etq2K7bmbY51Q7g853HLxJ7qEB2Snog9oRvDw%40mail.gmail.com
>>>>
>>>
>>> I don't understand why you come to that conclusion: both Masahiko Sawada
>>> and Jeff Janes have a DROP SUBSCRIPTION in the mix; my cases haven't. 
>>> Isn't that a real difference?
>>>
>>
> 
> Just noted another one issue/feature with snapshot builder — when logical 
> decoding is in progress
> and vacuum full command is being issued quite a big amount of files appears 
> in pg_logical/mappings
> and reside there till the checkpoint. Also having consequent vacuum full’s 
> before checkpoint yields even
> more files.
> 
> Having two pgbench-filled instances with logical replication between them:
> 
> for i in {1..100}; do psql -c 'vacuum full' && ls -la pg_logical/mappings | 
> wc -l; done;
> VACUUM
>       73
> VACUUM
>      454
> VACUUM
>     1146
> VACUUM
>     2149
> VACUUM
>     3463
> VACUUM
>     5088
> <...>
> VACUUM
>    44708
> <…> // checkpoint happens somewhere here
> VACUUM
>    20921
> WARNING:  could not truncate file "base/16384/61773": Too many open files in 
> system
> ERROR:  could not fsync file 
> "pg_logical/mappings/map-4000-4df-0_A4EA29F8-5aa5-5ae6": Too many open files 
> in system
> 
> 
> I’m not sure whether this is boils down to some of the previous issues 
> mentioned here or not, so posting
> here as observation.
> 

This has nothing to do with snapshot builder so this is not the thread
for it. See the comment section near the bottom of
src/backend/access/heap/rewriteheap.c for explanation of why it does
what it does.

-- 
  Petr Jelinek                  http://www.2ndQuadrant.com/
  PostgreSQL Development, 24x7 Support, Training & Services


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