Date: Mon, 25 Mar 2024 17:35:27 +0100
From: Dmitry Dolgov <9erthalion6@gmail.com>
To: Yasuo Honda <yasuo.honda@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Peter Smith <smithpb2250@gmail.com>,
	vignesh C <vignesh21@gmail.com>,
	Michael Paquier <michael@paquier.xyz>,
	Nathan Bossart <nathandbossart@gmail.com>,
	"Gregory Stark (as CFM)" <stark.cfm@gmail.com>,
	David Geier <geidav.pg@gmail.com>, Sergei Kornilov <sk@zsrv.org>,
	Alvaro Herrera <alvherre@alvh.no-ip.org>,
	Marcos Pegoraro <marcos@f10.com.br>,
	Robert Haas <robertmhaas@gmail.com>, Zhihong Yu <zyu@yugabyte.com>,
	David Steele <david@pgmasters.net>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>,
	Pavel Trukhanov <pavel.trukhanov@gmail.com>
Subject: Re: pg_stat_statements and "IN" conditions
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> On Sun, Mar 24, 2024 at 11:36:38PM +0900, Yasuo Honda wrote:
> Thanks for the information. I can apply these 4 patches from
> 0eb23285a2 . I tested this branch from Ruby on Rails and it gets some
> unexpected behavior from my point of view.
> Setting pg_stat_statements.query_id_const_merge_threshold = 5 does not
> normalize sql queries whose number of in clauses exceeds 5.
>
> Here are test steps.
> https://gist.github.com/yahonda/825ffccc4dcb58aa60e12ce33d25cd45#expected-behavior
>
> It would be appreciated if I can get my understanding correct.

From what I understand out of the description this ruby script uses
prepared statements, passing values as parameters, right? Unfortunately
the current version of the patch doesn't handle that, it works with
constants only [1]. The original incarnation of this feature was able to
handle that, but the implementation was considered to be not suitable --
thus, to make some progress, it was left outside.

The plan is, if everything goes fine at some point, to do a follow-up
patch to handle Params and the rest.

[1]: https://www.postgresql.org/message-id/20230211104707.grsicemegr7d3mgh%40erthalion.local