Subject: Re: BUG #16109: Postgres planning time is high across version (Expose
 buffer usage during planning in EXPLAIN)
To: Julien Rouhaud <rjuju123@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>, Andres Freund <andres@anarazel.de>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
References: <16109-26a1a88651e90608@postgresql.org>
 <20191112205506.rvadbx2dnku3paaw@alap3.anarazel.de>
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 <20200124055534.GM13621@telsasoft.com>
 <CAOBaU_ZhmG7FZBH9z28nb7++zQ--FsqX_GcTefXa7oj1yrWnRg@mail.gmail.com>
 <CAOBaU_YAN6PW4perkROgXWtRmDNX8tvKwjgDpsR6wYetEUahGQ@mail.gmail.com>
 <20200331013146.GA14618@telsasoft.com>
 <7bdd1e99-335f-a24a-ffbd-8a578a761970@oss.nttdata.com>
 <CAOBaU_ZrKOMXLxxeqUvuFN1Xy2Kfmz7GFfT47ksCuecC8N2AOQ@mail.gmail.com>
 <045faedf-108d-26e6-7307-ab1ac2d64624@oss.nttdata.com>
 <20200402060154.gylqmvwdbes5s5ni@nol>
From: Fujii Masao <masao.fujii@oss.nttdata.com>
Message-ID: <0abcbb8f-5b96-da04-ad7d-b84c36d09dd0@oss.nttdata.com>
Date: Thu, 2 Apr 2020 15:52:17 +0900
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On 2020/04/02 15:01, Julien Rouhaud wrote:
> On Thu, Apr 02, 2020 at 01:05:56PM +0900, Fujii Masao wrote:
>>
>>
>> On 2020/04/02 3:47, Julien Rouhaud wrote:
>>> On Wed, Apr 1, 2020 at 7:51 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
>>>>
>>>>
>>>> On 2020/03/31 10:31, Justin Pryzby wrote:
>>>>> On Wed, Jan 29, 2020 at 12:15:59PM +0100, Julien Rouhaud wrote:
>>>>>> Rebase due to conflict with 3ec20c7091e97.
>>>>>
>>>>> This is failing to apply probably since 4a539a25ebfc48329fd656a95f3c1eb2cda38af3.
>>>>> Could you rebase?   (Also, not sure if this can be set as RFC?)
>>>>
>>>> I updated the patch. Attached.
>>>
>>> Thanks a lot!  I'm sorry I missed Justin's ping, and it I just
>>> realized that my cron job that used to warn me about cfbot failure was
>>> broken :(
>>>
>>>> +/* Compute the difference between two BufferUsage */
>>>> +BufferUsage
>>>> +ComputeBufferCounters(BufferUsage *start, BufferUsage *stop)
>>>>
>>>> Since BufferUsageAccumDiff() was exported, ComputeBufferCounters() is
>>>> no longer necessary. In the patched version, BufferUsageAccumDiff() is
>>>> used to calculate the difference of buffer usage.
>>>
>>> Indeed, exposing BufferUsageAccumDiff wa definitely a good thing!
>>>
>>>> +       if (es->summary && (planduration || es->buffers))
>>>> +               ExplainOpenGroup("Planning", "Planning", true, es);
>>>>
>>>> Isn't it more appropriate to check "bufusage" instead of "es->buffers" here?
>>>> The patch changes the code so that "bufusage" is checked.
>>>
>>> AFAICS not unless ExplainOneQuery is also changed to pass a NULL
>>> pointer if the BUFFER option wasn't provided (and maybe also
>>> optionally skip the planning buffer computation).  With this version
>>> you now get:
>>>
>>> =# explain (analyze, buffers off) update t1 set id = id;
>>>                                                 QUERY PLAN
>>> -------------------------------------------------------------------------------------------------------
>>>    Update on t1  (cost=0.00..22.70 rows=1270 width=42) (actual
>>> time=0.170..0.170 rows=0 loops=1)
>>>      ->  Seq Scan on t1  (cost=0.00..22.70 rows=1270 width=42) (actual
>>> time=0.050..0.054 rows=1 loops=1)
>>>    Planning Time: 1.461 ms
>>>      Buffers: shared hit=25
>>>    Execution Time: 1.071 ms
>>> (5 rows)
>>>
>>> which seems wrong to me.
>>>
>>> I reused the es->buffers to avoid having needing something like:
>>
>> Yes, you're right! So I updated the patch as you suggested.
>> Attached is the updated version of the patch.
>> Thanks for the review!
> 
> 
> Thanks a lot, it all looks good to me!

Thanks! Barring any objection, I will commit the latest version of the patch.

Regards,

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