Stuart Bishop <stuart(dot)bishop(at)canonical(dot)com> writes:
> I would like to understand what causes some of my indexes to be slower to
> use than others with PostgreSQL 8.1.
I was about to opine that it was all about different levels of
correlation between the index order and physical table order ... but
your experiments with freshly clustered indexes seem to cast doubt
on that idea. Are you sure your function is really immutable? A buggy
function could possibly lead to a "clustered" index not being in
physical order.
regards, tom lane