From: Tom Lane <tgl@sss.pgh.pa.us>
To: Gurjeet Singh <gurjeet@singh.im>
cc: Ahmed Ibrahim <ahmed.ibr.hashim@gmail.com>,
        pgsql-hackers@lists.postgresql.org
Subject: Re: Issue in _bt_getrootheight
In-reply-to: <CABwTF4XSREc4f-OxMXWnO=d3RPud+ntibPNS0rhvYinxMSv0sg@mail.gmail.com>
References: <CAHiW8txjW0qHjeTEwNLGKuLgOPkNXF2TE-sozjSMeeD7uTm77A@mail.gmail.com> <CABwTF4XSREc4f-OxMXWnO=d3RPud+ntibPNS0rhvYinxMSv0sg@mail.gmail.com>
Comments: In-reply-to Gurjeet Singh <gurjeet@singh.im>
	message dated "Wed, 19 Jul 2023 20:45:41 -0700"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <971649.1689961316.1@sss.pgh.pa.us>
Content-Transfer-Encoding: quoted-printable
Date: Fri, 21 Jul 2023 13:41:56 -0400
Message-ID: <971650.1689961316@sss.pgh.pa.us>
Archived-At: <https://www.postgresql.org/message-id/971650.1689961316%40sss.pgh.pa.us>
Precedence: bulk

Gurjeet Singh <gurjeet@singh.im> writes:
> Please see attached the patch that does this. Let me know if this patch =
helps.

I don't like this patch one bit, because it adds a lot of overhead
(i.e., an extra index_open/close cycle for every btree index in every
query) to support a tiny minority use-case.  How come we don't
already know whether the index is hypothetical at the point where
_bt_getrootheight is called now?

Actually, looking at the existing comment at the call site:

    /*
     * Allow a plugin to editorialize on the info we obtained from the
     * catalogs.  Actions might include altering the assumed relation size=
,
     * removing an index, or adding a hypothetical index to the indexlist.
     */
    if (get_relation_info_hook)
        (*get_relation_info_hook) (root, relationObjectId, inhparent, rel)=
;

reminds me that the design intention was that hypothetical indexes
would get added to the list by get_relation_info_hook itself.
If that's not how the index adviser is operating, maybe we need
to have a discussion about that.

			regards, tom lane