On Mon, Oct 28, 2024 at 3:54 PM David Rowley <dgrowle...@gmail.com> wrote:
> On Wed, 23 Oct 2024 at 13:51, David G. Johnston > <david.g.johns...@gmail.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. That was partially the point of writing "all" there - absent other information, and seeing how index-only scans were treated, I presumed it was indeed actually or effectively a switch for all. If it is not it should be made clear which node types with the word index in them are not affected. I think > it's better to explicitly mention index-only-scans to make it clear > which nodes are affected. > I hadn't considered Bitmap Index Scans but I would expect if you do not use index scans then the ability to produce bitmaps from them would be precluded. I could see pointing out, in enable_bitmapscan, that enable_bitmapscan is effectively disabled (for index inputs) when enable_indexscan is set to off. Then, in enable_indexscan, add a "see also" to enable_bitmapscan with a brief reason as well. Is there a listing of all node types produced by PostgreSQL (with the explain output naming) along with which ones are affected by which enable_* knobs (possibly multiple for something like Bitmap Index Scan)? > + 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? > I prefer to briefly explain why we advise the reader to go "see also" here. > - 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'd like to stick with a conjunction there but agree the "must be enabled" wording is preferrable, avoiding the double-negative. "The default is on, but the <xref> setting must also be enabled." The 'to have the...' part seems to just be redundant. David J.
