Date: Sat, 2 May 2020 02:08:18 +0200
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Fujii Masao <masao.fujii@oss.nttdata.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>,
	Masahiko Sawada <masahiko.sawada@2ndquadrant.com>,
	"tsunakawa.takay@fujitsu.com" <tsunakawa.takay@fujitsu.com>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: SLRU statistics
Message-ID: <20200502000818.nn4kpewiput42bnb@development>
References: <20200229122441.ow7gnnqgesmojyc3@development>
 <20200229144426.GA32500@alvherre.pgsql>
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 <20200327004111.md4suoi6u5suv2qe@development>
 <20200328002630.2nz5y3dvymqnvxtv@development>
 <20200402004136.wodwftan45mcwggm@development>
 <f02fd0ec-a240-b5bf-9992-5faf582738f1@oss.nttdata.com>
 <20200430181901.24tlriahmafi4sfn@development>
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On Fri, May 01, 2020 at 11:49:51AM +0900, Fujii Masao wrote:
>
>
>On 2020/05/01 3:19, Tomas Vondra wrote:
>>On Fri, May 01, 2020 at 03:02:59AM +0900, Fujii Masao wrote:
>>>
>>>
>>>On 2020/04/02 9:41, Tomas Vondra wrote:
>>>>Hi,
>>>>
>>>>I've pushed this after some minor cleanup and improvements.
>>>
>>>+static char *slru_names[] = {"async", "clog", "commit_timestamp",
>>>+                              "multixact_offset", "multixact_member",
>>>+                              "oldserxid", "pg_xact", "subtrans",
>>>+                              "other" /* has to be last */};
>>>
>>>When I tried pg_stat_slru, I found that it returns a row for "pg_xact".
>>>But since there is no "pg_xact" slru ("clog" slru exists instead),
>>>"pg_xact" should be removed? Patch attached.
>>>
>>
>>Yeah, I think I got confused and accidentally added both "clog" and
>>"pg_xact". I'll get "pg_xact" removed.
>
>Thanks!
>

OK, pushed. Thanks!

>Another thing I found is; pgstat_send_slru() should be called also by
>other processes than backend? For example, since clog data is flushed
>basically by checkpointer, checkpointer seems to need to send slru stats.
>Otherwise, pg_stat_slru.flushes would not be updated.
>

Hmmm, that's a good point. If I understand the issue correctly, the
checkpointer accumulates the stats but never really sends them because
it never calls pgstat_report_stat/pgstat_send_slru. That's only called
from PostgresMain, but not from CheckpointerMain.

I think we could simply add pgstat_send_slru() right after the existing
call in CheckpointerMain, right?

regards

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