Date: Tue, 21 Jan 2020 14:56:14 +0100
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Masahiko Sawada <masahiko.sawada@2ndquadrant.com>
Cc: "tsunakawa.takay@fujitsu.com" <tsunakawa.takay@fujitsu.com>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: SLRU statistics
Message-ID: <20200121135614.vt4cpuzwiyarzfca@development>
References: <20200119143707.gyinppnigokesjok@development>
 <OSAPR01MB5073426AFE2F2A524948FA6CFE320@OSAPR01MB5073.jpnprd01.prod.outlook.com>
 <20200120163754.mbbkbhzaummlo47c@development>
 <CA+fd4k79ngs-vjAeLXhMyy1FGgXSqGdCnWW-mR0By5vzgLO47g@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Disposition: inline
In-Reply-To: 
 <CA+fd4k79ngs-vjAeLXhMyy1FGgXSqGdCnWW-mR0By5vzgLO47g@mail.gmail.com>
Precedence: bulk

On Tue, Jan 21, 2020 at 05:09:33PM +0900, Masahiko Sawada wrote:
>On Tue, 21 Jan 2020 at 01:38, Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:
>>
>> On Mon, Jan 20, 2020 at 01:04:33AM +0000, tsunakawa.takay@fujitsu.com wrote:
>> >From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
>> >> One of the stats I occasionally wanted to know are stats for the SLRU
>> >> stats (we have couple of those - clog, subtrans, ...). So here is a WIP
>> >> version of a patch adding that.
>
>+1
>
>> >
>> >How can users take advantage of this information?  I think we also need
>> >the ability to set the size of SLRU buffers.  (I want to be freed from
>> >the concern about the buffer shortage by setting the buffer size to its
>> >maximum.  For example, CLOG would be only 1 GB.)
>> >
>>
>> You're right the users can't really take advantage of this - my primary
>> motivation was providing a feedback for devs, benchmarking etc. That
>> might have been done with DEBUG messages or something, but this seems
>> more convenient.
>
>I've not tested the performance impact but perhaps we might want to
>disable these counter by default and controlled by a GUC. And similar
>to buffer statistics it might be better to inline
>pgstat_count_slru_page_xxx function for better performance.
>

Hmmm, yeah. Inlining seems like a good idea, and maybe we should have
something like track_slru GUC.


regards

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