Date: Tue, 17 Sep 2019 15:01:38 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Alexander Korotkov <a.korotkov@postgrespro.ru>
Cc: Andres Freund <andres@anarazel.de>,
	Nikita Glukhov <n.gluhov@postgrespro.ru>,
	Thomas Munro <thomas.munro@gmail.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>,
	Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>,
	David Steele <david@pgmasters.net>,
	Michael Paquier <michael@paquier.xyz>
Subject: Re: Psql patch to show access methods info
Message-ID: <20190917180138.GA12497@alvherre.pgsql>
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It seems strange that there's a way to display AMs, and a way to display
ops and procs in an opfamily; but there's no way to list what opfamilies
exist (possibly given an AM as pattern).  Should we add that too?  We
had \dAf in the original submission, but that seems to have lost along
the way, not sure why.

I think \dAf is just as critical as \dAo; the former lets you know which
opfamilies you can use in CREATE INDEX, while the latter lets you know
which operators would be helped by such an index.  (But, really, only if
the opfamily name is printed in \d of the index, which we currently
don't print unless it's non-default ... which is an omission that
perhaps we should consider fixing).

On the other hand, from a user perspective, what you really want to know
is: what opfamilies exist for datatype T, and what operators are
supported by the opfamily I have chosen?  The current patch doesn't
really help you find that out.

I think \dAp isn't terribly informative from a user perspective.  The
support procs are just an opfamily implementation detail.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services