Re: simple join uses indexes, very slow

> -----Original Message-----
> From: pgsql-performance-owner(at)postgresql(dot)org
[mailto:pgsql-performance-
> owner(at)postgresql(dot)org] On Behalf Of Steinar H. Gunderson
> Sent: Tuesday, March 28, 2006 10:29 AM
>
> An index on (A,B,C) can be used for a query on (A,B) or (A), so it
doesn't
> really matter. It isn't usable for a query on (B), (C) or (B,C),
though.
> (The
> index rows will get bigger, of course, so you'll need more I/O if you
want
> to
> scan large parts of it, but I guess that's beside the point.)

I guess what I am really curious about is why was the OP getting an
expensive sort when the planner tried a merge join? Most of the time
was spent sorting the parameters parameters table by opset_num even
though opset_num is indexed. Isn't Postgres able to walk the index
instead of sorting? I was wondering if maybe Postgres wasn't
recognizing that it could just walk the index because the opset_num
column isn't the first in the index.