Re: Tuning Question

A copy of this was sent to rspeaker_at_my-dejanews.com (if that email address didn't require changing) On Tue, 29 Dec 1998 20:04:27 GMT, you wrote:

>I have just finished analyzing a report.txt from an Oracle 8 database, and I
>have a question on the 'cluster key scan' related fields. The reference
>material from my performance tuning class states that the degree of cluster
>key chaining (cluster key scans block gets / cluster scans) should be less
>than 1. This particular instance is reporting a degree of 2.75. What if any
>impact will this have on my database performance?
>
>Thanks.
>Roy Speaker
>
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If this ratio is greater than one the rows for one cluster key are stored in multiple data blocks. Whether this is acceptable or not depends on the data making up the cluster. If your application has no clusters these figures are still generally populated as some dictionary tables are defined as clusters. It is quite normal for these to have a value > 1 for this ratio.

For application clusters a ratio > 1 may indicate:

• Nothing abnormal at all if the cluster may have lots of rows for each cluster key (as the data dictionary does).
  • Too many cluster keys per block when the cluster was defined (the default is one key per block so problem would be self inflicted)
  • Row chaining

Thomas Kyte
tkyte_at_us.oracle.com
Oracle Service Industries
Reston, VA USA

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