Re: Regarding query minimizer (simplifier) - Mailing list pgsql-hackers

Hello, 

We appreciate you taking time for test! When we do more evaluation, we noticed that the previously attached query made regression only on DBs that we installed from APT manager (i.e., apt-get command) not on DBs that we built from the source code. But we also confirmed that there are many cases that cause regression to all DBs (installed from APT and build from source code)

Hope you can also test these queries too. These are the execution time on our machine.

1.sql

10.5  : 20ms

9.4.19: 1,227ms

4.sql

10.5  : 13ms

9.4.19: 88,721ms

20.sql

10.5  : 271ms

9.4.19: 6,104ms

22.sql

10.5  : 8ms

9.4.19: 105ms

Jinho Jung

On Tue, Oct 23, 2018 at 9:52 AM Jung, Jinho <jinho.jung@gatech.edu> wrote:

Hello Tom, 

Sorry for the misleading. Could you try these two queries? I made the query even slower in latest version of postgres. These are information about how we set up evaluation environment and query result. 

Thanks,

Jinho Jung

Install Multiple version of DBs in one machine

======================================

# Install 10.5

    $ wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -        

    $ sudo sh -c 'echo "deb http://apt.postgresql.org/pub/repos/apt/ xenial-pgdg main" > /etc/apt/sources.list.d/pgdg_xenial.list'

    $ sudo apt update

    $ sudo apt-get install postgresql-10

# Install 9.6

    $ sudo apt-get install postgresql-9.6 

# Install 9.5

    $ sudo apt-get install postgresql-9.5

# Install 9.4 

    $ sudo apt-get install postgresql-9.4 postgresql-contrib-9.4 libpq-dev postgresql-server-dev-9.4

# check 

    $ pg_lsclusters

Original regression query

==========================

explain analyze

select

  1

from

  information_schema.role_usage_grants as ref_2,

  lateral (

    select

      max((null)) over (partition by ref_3.amopfamily) as c8

    from

        pg_catalog.pg_amop as ref_3

    ) as subq_0

;

ORIGINAL querying time

on old version(9.4/9.5): 5.7ms

on latest version(10): 91.76ms

CORRELATED query to maximize error

===================================

explain analyze

select *

from information_schema.role_usage_grants f1

where grantor = 

    ( select max(ref_2.grantor)

      from

       information_schema.role_usage_grants as ref_2,

       lateral (

         select

           max((null)) over (partition by ref_3.amopfamily) as c8

         from

             pg_catalog.pg_amop as ref_3

         ) as subq_0

      where ref_2.object_catalog = f1.object_catalog

    )

;

CORRELATED querying time

on old version(9.4/9.5): 0.6s

on latest version(10): 113s

188 times slower

---

From: Tom Lane <tgl@sss.pgh.pa.us>
Sent: Saturday, October 13, 2018 5:59:06 PM
To: Jung, Jinho
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Regarding query minimizer (simplifier)

 

"Jung, Jinho" <jinho.jung@gatech.edu> writes:
> Hello, I am Jinho Jung, Phd Student from GeorgiaTech, and try to find any SQL queries that cause performance regression. While conducting evaluation, I found an interesting query which makes x80 times slower execution in version 10.5 than version 9.4. Please see the attached files, if you are interested.

Hm, testing this in the regression database, it seems pretty speedy
across all supported branches, and indeed slower in 9.4 than later
branches (~25 ms vs ~10 ms).

It seems likely that you're testing in a very different database,
perhaps one with many more tables ... but if you don't explain the
test scenario, we aren't going to have much luck investigating.

                        regards, tom lane