From: Thomas Kellerer <shammat@gmx.net>
To: pgsql-performance@lists.postgresql.org
Subject: Re: Potential performance issues
Date: Mon, 1 Mar 2021 15:44:02 +0100
Message-ID: <5fcce4e3-3ee7-e516-91a6-1883def57de8@gmx.net> (raw)
In-Reply-To: <BN6PR07MB313763C4040616159DE1B6FBEE9B9@BN6PR07MB3137.namprd07.prod.outlook.com>
References: <BN6PR07MB313763C4040616159DE1B6FBEE9B9@BN6PR07MB3137.namprd07.prod.outlook.com>
Jung, Jinho schrieb am 28.02.2021 um 16:04:
> # Performance issues discovered from differential test
>
> For example, the below query runs x1000 slower than other DBMSs from PostgreSQL.
>
> select ref_0.ol_amount as c0
> from order_line as ref_0
> left join stock as ref_1
> on (ref_0.ol_o_id = ref_1.s_w_id )
> inner join warehouse as ref_2
> on (ref_1.s_dist_09 is NULL)
> where ref_2.w_tax is NULL;
I find this query extremely weird to be honest.
There is no join condition between warehouse and the other two tables which results in a cross join.
Which is "reduced" somehow by applying the IS NULL conditions - but still, to me this makes no sense.
Maybe the Postgres optimizer doesn't handle this ugly "join condition" the same way the others do.
I would rather expect a NOT EXISTS against the warehouse table.
Thomas
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Cc: shammat@gmx.net, pgsql-performance@lists.postgresql.org
Subject: Re: Potential performance issues
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