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From: Anastasia Lubennikova <[email protected]>
To: Julien Rouhaud <[email protected]>
To: Pavel Stehule <[email protected]>
Cc: [email protected]
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: [PATCH] Add extra statistics to explain for Nested Loop
Date: Sat, 17 Oct 2020 01:11:24 +0300
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAOBaU_YHfFcE3HPjW1Db-qOYNZuAMw3Cjv_pFRaRAQTQy+HE0g@mail.gmail.com>
References: <[email protected]>
	<CAFj8pRA=wMP+yebbssQByL9nV5FJe6vnkw-ZB7zta1j2W9ftjg@mail.gmail.com>
	<CAOBaU_YHfFcE3HPjW1Db-qOYNZuAMw3Cjv_pFRaRAQTQy+HE0g@mail.gmail.com>

On 16.10.2020 12:07, Julien Rouhaud wrote:
> Le ven. 16 oct. 2020 à 16:12, Pavel Stehule <[email protected] 
> <mailto:[email protected]>> a écrit :
>
>
>
>     pá 16. 10. 2020 v 9:43 odesílatel <[email protected]
>     <mailto:[email protected]>> napsal:
>
>         Hi, hackers.
>         For some distributions of data in tables, different loops in
>         nested loop
>         joins can take different time and process different amounts of
>         entries.
>         It makes average statistics returned by explain analyze not
>         very useful
>         for DBA.
>         To fix it, here is the patch that add printing of min and max
>         statistics
>         for time and rows across all loops in Nested Loop to EXPLAIN
>         ANALYSE.
>         Please don't hesitate to share any thoughts on this topic!
>
>
>     +1
>
>     This is great feature - sometimes it can be pretty messy current
>     limited format
>
>
> +1, this can be very handy!
>
Cool.
I have added your patch to the commitfest, so it won't get lost.
https://commitfest.postgresql.org/30/2765/

I will review the code next week.  Unfortunately, I cannot give any 
feedback about usability of this feature.

User visible change is:

-               ->  Nested Loop (actual rows=N loops=N)
+              ->  Nested Loop (actual min_rows=0 rows=0 max_rows=0 loops=2)

Pavel, Julien, could you please say if it looks good?

-- 
Anastasia Lubennikova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

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