From: Tom Lane <tgl@sss.pgh.pa.us>
To: jian xu <jamesxu@outlook.com>
cc: "pgsql-admin@lists.postgresql.org" <pgsql-admin@lists.postgresql.org>
Subject: Re: how to troubleshoot a wrong query plan
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Comments: In-reply-to jian xu <jamesxu@outlook.com>
	message dated "Wed, 27 Dec 2023 21:15:08 +0000"
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Date: Wed, 27 Dec 2023 16:21:51 -0500
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jian xu <jamesxu@outlook.com> writes:
> Sorry, we figured out that the PostgreSQL.conf has the nestloop disabled=
=C2=85.that=C2=92s why It picked merge join by default
> But it might be still very helpful if there is a way to show how the pla=
n is generated , or some debug information about the plan generating, for =
example in this case, if we can debug the plan and see nestloop is disable=
, it will be easy for us figure out the problem.

In supported releases of PG, there's the EXPLAIN (SETTINGS) option, which
will print the values of any non-default settings that affect planning.
Of course, you have to remember to use that, but it does respond to
your point.

			regards, tom lane