Horton

Re: Get memory contexts of an arbitrary backend process

Fujii Masao <masao.fujii@oss.nttdata.com>

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From: Fujii Masao <masao.fujii@oss.nttdata.com>
To: torikoshia <torikoshia@oss.nttdata.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Georgios Kokolatos <gkokolatos@protonmail.com>, Kasahara Tatsuhito <kasahara.tatsuhito@gmail.com>, craig@2ndquadrant.com
Date: 2021-03-05T05:22:56Z
Lists: pgsql-hackers 

On 2021/03/04 18:32, torikoshia wrote:
> On 2021-01-14 19:11, torikoshia wrote:
>> Since pg_get_target_backend_memory_contexts() waits to dump memory and
>> it could lead dead lock as below.
>>
>>   - session1
>>   BEGIN; TRUNCATE t;
>>
>>   - session2
>>   BEGIN; TRUNCATE t; -- wait
>>
>>   - session1
>>   SELECT * FROM pg_get_target_backend_memory_contexts(<pid of session
>> 2>); --wait
>>
>>
>> Thanks for notifying me, Fujii-san.
>>
>>
>> Attached v8 patch that prohibited calling the function inside transactions.
> 
> Regrettably, this modification could not cope with the advisory lock and
> I haven't come up with a good way to deal with it.
> 
> It seems to me that the architecture of the requestor waiting for the
> dumper leads to this problem and complicates things.
> 
> 
> Considering the discussion printing backtrace discussion[1], it seems
> reasonable that the requestor just sends a signal and dumper dumps to
> the log file.

+1

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION

Commits

  1. Add function to log the memory contexts of specified backend process.

  2. Add pg_backend_memory_contexts system view.

  3. Limit the verbosity of memory context statistics dumps.