Trevor Talbot wrote:
On 10/4/07, John Stanton <[EMAIL PROTECTED]> wrote:
A B-Tree index holds keys in sorted sequence. They are in random
sequence in the database. That requires holding the keys in the B-Tree
nodes.
Actually, it doesn't strictly require that; it could store references
to the keys. An obvious tradeoff is I/O; an index walk is less useful
if you have to do random seeks to the locations of row data just to
get the keys to walk the tree in the first place. IOW in simplistic
terms, an index walk suddenly doubles in disk I/O.
The information on SQL Server would be interesting, as I know it
stores sort keys under some conditions, which is effectively duplicate
data.
One would need to be a paleontologist to measure the performance of an
ordered index with indirect key references.
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