Re: Adding skip scan (including MDAM style range skip scan) to nbtree

On Tue, Jul 2, 2024 at 12:55 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> Although v2 gives correct answers to the queries, the scan itself
> performs an excessive amount of leaf page accesses. In short, it
> behaves just like a full index scan would, even though we should
> expect it to skip over significant runs of the index. So that's
> another bug.

Hit "send" too soon. I simply forgot to run "alter table test1 alter
column c type "char";" before running the query. So, I was mistaken
about there still being a bug in v2. The issue here is that we don't
have support for the underlying type, char(1) -- nothing more.

v2 of the patch with your query 1 (when changed to use the "char"
type/opclass instead of the currently unsupported char(1)
type/opclass) performs 395 index related buffer hits, and 5406 heap
block accesses. Whereas it's 3833 index buffer hits with master
(naturally, the same 5406 heap accesses are required with master). In
short, this query isn't particularly sympathetic to the patch. Nor is
it unsympathetic.

--
Peter Geoghegan