Re: EXPLAIN IndexOnlyScan shows disabled when enable_indexonlyscan=on

From: David Rowley <dgrowleyml(at)gmail(dot)com>
To: "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>
Cc: Melanie Plageman <melanieplageman(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>
Subject: Re: EXPLAIN IndexOnlyScan shows disabled when enable_indexonlyscan=on
Date: 2024-10-28 22:54:01
Message-ID: CAApHDvrR=0ExMOEQvnwWfck2NSk=_pktwNDvybYS-ziB74kT1w@mail.gmail.com
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On Wed, 23 Oct 2024 at 13:51, David G. Johnston
<david(dot)g(dot)johnston(at)gmail(dot)com> wrote:
> Went with a slightly different wording that seems to flow better with the xrefs I added between the two options.

- Enables or disables the query planner's use of index-scan plan
- types. The default is <literal>on</literal>.
+ Enables or disables the query planner's use of all index-scan
related plan

I'm concerned about the wording "all index-scan related". It's not
that clear if that would include Bitmap Index Scans or not. I think
it's better to explicitly mention index-only-scans to make it clear
which nodes are affected.

+ types. The default is <literal>on</literal>. The
index-only-scan plan types
+ can be independently disabled by setting <xref
linkend="guc-enable-indexonlyscan"/>
+ to <literal>off</literal>.

I wondered if it's better to reference the enable_indexonlyscan GUC
here rather than document what enable_indexonlyscan does from the
enable_indexscan docs. Maybe just a "Also see enable_indexonlyscans."
could be added?

- The default is <literal>on</literal>.
+ The default is <literal>on</literal>. However, this setting
has no effect if
+ <xref linkend="guc-enable-indexscan"/> is set to
<literal>off</literal>.

Could we just add "The <xref linkend="guc-enable-indexscan"/> setting
must also be enabled to have the query planner consider
index-only-scans"?

I've attached that in patch form.

David

Attachment Content-Type Size
runtime-config-query.html text/html 47.8 KB
v2_enable_indexscan_docs.patch application/octet-stream 1.2 KB

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