On Fri, May 23, 2025 at 5:03 PM Bruce Momjian <bruce@momjian.us> wrote:
> I was able to squeeze in this detail in the attached, applied patch.
I noticed that Crunchy Data had a blog post about the skip scan, where
the author got tripped up by the description of skip scan that current
appears in the release notes.
See: https://www.crunchydata.com/blog/get-excited-about-postgres-18
The blog post incorrectly says "Note that this optimization only works
for queries which use the = operator, so it will not work with
inequalities or ranges". This is incorrect; skip scan works perfectly
fine with inequality operators. I'm sure that this confusion arose
because of the wording from the release notes.
Adding to the confusion, Crunchy also had a Tweet about skip scan that
used an inequality operator (which will work correctly):
https://x.com/crunchydata/status/1965751871848468499
I'm sure that this was due to the release note description, since
there was some discussion of it on a LinkedIn post that promoted the
blog post.
In light of all this, I propose that we change the current feature
description, from:
"This allows multi-column btree indexes to be used by queries that
only equality-reference the second or later indexed columns."
to:
"This allows multi-column btree indexes to be used by queries that
only specify conditions on the second or later indexed columns."
--
Peter Geoghegan
