Re: 2 Oracle doubts

From: Tanel Poder <tanel_at_@peldik.com>
Date: Fri, 25 Jul 2003 22:20:30 +0300
Message-ID: <3f2182fc$1_1@news.estpak.ee>

One more reason that came into my mind, is that keys in index leaf block are always ordered. That makes scanning faster, for exaple when the wanted value doesn't exist in table...

Tanel.

> Why such difference? One reason is that with full table scan segment
header block (or more in case of big segment) has to be visited, to find out where the extents of segment are, but for indexes no such operation is done. You can verify it with 10046 trace, with index access you see one sequential read, with table you see one sequential and one scattered read... Received on Fri Jul 25 2003 - 14:20:30 CDT