From: Tom Lane <tgl@sss.pgh.pa.us>
To: Fabian Lindfors <fabian@flapplabs.se>
cc: pgsql-general@postgresql.org
Subject: Re: Custom index access method for primary keys
In-reply-to: <872B0CA7-4483-4FC2-8CD8-0A5C08FC0942@flapplabs.se>
References: <872B0CA7-4483-4FC2-8CD8-0A5C08FC0942@flapplabs.se>
Comments: In-reply-to Fabian Lindfors <fabian@flapplabs.se>
	message dated "Sat, 05 Apr 2025 12:34:24 +0200"
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Date: Mon, 07 Apr 2025 10:06:48 -0400
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Fabian Lindfors <fabian@flapplabs.se> writes:
> Hi! I=E2=80=99m working on an index access method that I intend to be
> generic and to replace btree for my specific use case. I noticed
> though that it doesn=E2=80=99t seem to be possible to specify an access
> method when creating a new table and using PRIMARY KEY.

There's some work going on right now to remove the core code's
assumptions that only btree can handle unique/pkey constraints
and sorting [1].  I'm not sure if it'll be entirely complete for
v18 but the goalposts have been moved quite far.  I think you can
probably expect to be able to do

	CREATE TABLE mytable ...;
	CREATE UNIQUE INDEX myindex ON mytable USING myam (...);
	ALTER TABLE mytable ADD PRIMARY KEY USING INDEX myindex;

It doesn't look like we yet allow direct "USING myam" in
PRIMARY KEY, but sooner or later we might get to that.

			regards, tom lane

[1] https://www.postgresql.org/message-id/flat/E72EAA49-354D-4C2E-8EB9-255=
197F55330%40enterprisedb.com