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From: Pavel Stehule <pavel.stehule@gmail.com>
Date: Wed, 11 Oct 2017 13:11:17 +0200
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 <CAFj8pRDnW+bD5OmWjawxryv_=BctsE8HF5Y1n=oxgQ+xwrVqUQ@mail.gmail.com>
Subject: Re: performance drop after upgrade (9.6 > 10)
To: =?UTF-8?Q?johannes_gra=C3=ABn?= <johannes@selfnet.de>
Cc: "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
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2017-10-11 13:06 GMT+02:00 johannes gra=C3=ABn <johannes@selfnet.de>:

> Hi,
>
> I wrote a query that joins several tables usually returning less than
> 1000 rows, groups them and generates a JSON object of the result. In
> 9.6 is was a question of milliseconds for that query to return the
> requested data. Now, after upgrading to 10, the query never returns -
> at least it hasn't returned in the last hour.
>
> To see what happens, I requested the query plan [1]. It looks complex
> and shows a lot of parallelization. I don't have the query plan from
> 9.6, but I remember it being considerably simpler.
>
> Can anyone have a guess what altered the performance here so
> dramatically? Is there a way to disable new parallelization features
> just for this query to see if it makes any difference?
>
>

have you fresh statistics? After upgrade is necessary to run ANALYZE comman=
d

Regards

Pavel


Best
>   Johannes
>
>
> [1] https://explain.depesz.com/s/xsPP
>
>
> --
> Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org=
)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-performance
>

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<div dir=3D"ltr"><br><div class=3D"gmail_extra"><br><div class=3D"gmail_quo=
te">2017-10-11 13:06 GMT+02:00 johannes gra=C3=ABn <span dir=3D"ltr">&lt;<a=
 href=3D"mailto:johannes@selfnet.de" target=3D"_blank">johannes@selfnet.de<=
/a>&gt;</span>:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 =
.8ex;border-left:1px #ccc solid;padding-left:1ex">Hi,<br>
<br>
I wrote a query that joins several tables usually returning less than<br>
1000 rows, groups them and generates a JSON object of the result. In<br>
9.6 is was a question of milliseconds for that query to return the<br>
requested data. Now, after upgrading to 10, the query never returns -<br>
at least it hasn&#39;t returned in the last hour.<br>
<br>
To see what happens, I requested the query plan [1]. It looks complex<br>
and shows a lot of parallelization. I don&#39;t have the query plan from<br=
>
9.6, but I remember it being considerably simpler.<br>
<br>
Can anyone have a guess what altered the performance here so<br>
dramatically? Is there a way to disable new parallelization features<br>
just for this query to see if it makes any difference?<br>
<br></blockquote><div><br></div><div><br></div><div>have you fresh statisti=
cs? After upgrade is necessary to run ANALYZE command<br></div><div><br></d=
iv><div>Regards</div><div><br></div><div>Pavel<br></div><div><br></div><div=
> <br></div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;bo=
rder-left:1px #ccc solid;padding-left:1ex">
Best<br>
=C2=A0 Johannes<br>
<br>
<br>
[1] <a href=3D"https://explain.depesz.com/s/xsPP" rel=3D"noreferrer" target=
=3D"_blank">https://explain.depesz.com/s/<wbr>xsPP</a><br>
<span class=3D"HOEnZb"><font color=3D"#888888"><br>
<br>
--<br>
Sent via pgsql-performance mailing list (<a href=3D"mailto:pgsql-performanc=
e@postgresql.org">pgsql-performance@postgresql.<wbr>org</a>)<br>
To make changes to your subscription:<br>
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rformance</a><br>
</font></span></blockquote></div><br></div></div>

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