Re: Regarding query minimizer (simplifier)

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(dot)jung(at)gatech(dot)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(at)sss(dot)pgh(dot)pa(dot)us>
> *Sent:* Saturday, October 13, 2018 5:59:06 PM
> *To:* Jung, Jinho
> *Cc:* pgsql-hackers(at)lists(dot)postgresql(dot)org
> *Subject:* Re: Regarding query minimizer (simplifier)
>
> "Jung, Jinho" <jinho(dot)jung(at)gatech(dot)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
>