From: Tom Lane <tgl@sss.pgh.pa.us>
To: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: Peter <pmc@citylink.dinoex.sub.org>
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: Should from_collapse be switched off? (queries 10 times faster)
Date: Fri, 23 Mar 2018 10:14:19 -0400
Message-ID: <18405.1521814459@sss.pgh.pa.us> (raw)
In-Reply-To: <1521805295.2471.40.camel@cybertec.at>
References: <20180323100308.GA1188@gate.oper.dinoex.org>
<1521805295.2471.40.camel@cybertec.at>
Laurenz Albe <laurenz.albe@cybertec.at> writes:
> Peter wrote:
>> I could not find any documentation or evaluation that would say
>> that from_collapse can have detrimental effects. Even less, which
>> type of queries may suffer from that.
> https://www.postgresql.org/docs/current/static/explicit-joins.html
> states towards the end of the page that the search tree grows
> exponentially with the number of relations, and from_collapse_limit
> can be set to control that.
It's conceivable that the OP's problem is actually planning time
(if the query joins sufficiently many tables) and that restricting
the cost of the join plan search is really what he needs to do.
Lacking any further information about the problem, we can't say.
We can, however, point to
https://wiki.postgresql.org/wiki/Slow_Query_Questions
concerning how to ask this type of question effectively.
regards, tom lane
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, laurenz.albe@cybertec.at, pmc@citylink.dinoex.sub.org, pgsql-performance@lists.postgresql.org
Subject: Re: Should from_collapse be switched off? (queries 10 times faster)
In-Reply-To: <18405.1521814459@sss.pgh.pa.us>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox