Re: Psql patch to show access methods info

On Tue, Sep 17, 2019 at 9:01 PM Alvaro Herrera <alvherre@2ndquadrant.com> wrote:
> 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 you have a point.  Will add \dAf command to the patch.

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

I've expressed my opinion regarding \dAp in [1].  In my observations,
some advanced users can write btree/hash opclasses in pl/* languages.
This doesn't require knowledge of core developer.  And they may find
\dAp command useful.  What do you think?

Links
1. https://www.postgresql.org/message-id/CAPpHfdtj_w20hTr4fHW4MnpL-pPGU3Mw0A9pRTRBL_XP-WGsyQ%40mail.gmail.com

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company