Re: Is this a good definition for clustering factor

Why invent another wheel? What is wrong with Oracle's definition? Oracle 9i (9.2) Database Reference:
Indicates the amount of order of the rows in the table based on the values=
=20

of the index.
- If the value is near the number of blocks, then the table is very well=20 ordered. In this case, the index entries in a single leaf block tend to=20 point to rows in the same data blocks.
- If the value is near the number of rows, then the table is veryrandomly=20 ordered. In this case, it is unlikely that index entries in the same leaf=20 block point to rows in the same data blocks.

and Oracle 9i (9.2) Database Performance Tuning Guide and Reference: The cost of fetching rows using rowids depends on the index clustering=20 factor. Although the clustering factor is a property of the index, the=20 clustering factor actually relates to the spread of similar indexed column=
=20

values within data blocks in the table. A lower clustering factor indicates=
=20

that the individual rows are concentrated within fewer blocks in the table.=
=20

Conversely, a high clustering factor indicates that the individual rows are=
=20

scattered more randomly across blocks in the table. Therefore, a high=20 clustering factor means that it costs more to use a range scan to fetch=20 rows by rowid, because more blocks in the table need to be visited to=20 return the data.

I see no need to =EFmprove" on these definitions. There is even an example=  in=20
the Tuning Guide.

Regards

Wolfgang Breitling
Centrex Consulting Corporation
http://www.centrexcc.com=20

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