Re: Is this a good definition for clustering factor
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: juancarlosreyesp@xxxxxxxxx
- Date: Wed, 16 Feb 2005 18:18:35 -0700
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
--
//www.freelists.org/webpage/oracle-l
Other related posts:
