Re: Showing primitive index scan count in EXPLAIN ANALYZE (for skip scan and SAOP scans)

On Thu, 15 Aug 2024 at 21:23, Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
>
> Attached patch has EXPLAIN ANALYZE display the total number of
> primitive index scans for all 3 kinds of index scan node. This is
> useful for index scans that happen to use SAOP arrays. It also seems
> almost essential to offer this kind of instrumentation for the skip
> scan patch [1]. Skip scan works by reusing all of the Postgres 17 work
> (see commit 5bf748b8) to skip over irrelevant sections of a composite
> index with a low cardinality leading column, so it has all the same
> issues.

Did you notice the patch over at [0], where additional diagnostic
EXPLAIN output for btrees is being discussed, too? I'm asking, because
I'm not very convinced that 'primitive scans' are a useful metric
across all (or even: most) index AMs (e.g. BRIN probably never will
have a 'primitive scans' metric that differs from the loop count), so
maybe this would better be implemented in that framework?

Kind regards,

Matthias van de Meent
Neon (https://neon.tech)

[0] https://www.postgresql.org/message-id/flat/TYWPR01MB10982D24AFA7CDC273445BFF0B1DC2%40TYWPR01MB10982.jpnprd01.prod.outlook.com#9c64cf75179da8d657a5eab7c75be480