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analyze compute and estimate

Posted on 2002-04-11
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Last Modified: 2008-02-01
I have only these points left at present, but A grade is certain. With analyze command, in brief, what is diff. between compute and estimate.
--- mundial
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Question by:mundial
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FarazMSyed earned 5 total points
ID: 6936050
hi there !!!

Oracle generates statistics using the following techniques:

- Estimation based on random data sampling
- Exact computation
- User-defined statistics collection methods

To perform an exact computation, Oracle requires enough space to perform a scan and sort of the table. If there is not enough space in memory, then temporary space may be required. For estimations, Oracle requires enough space to perform a scan and sort of only the rows in the requested sample of the table. For indexes, computation does not take up as much time or space, so it is best to perform a full computation.

Some statistics are always computed exactly, such as the number of data blocks currently containing data in a table or the depth of an index from its root block to its leaf blocks.

To estimate statistics, Oracle selects a random sample of data. You can specify the sampling percentage and whether sampling should be based on rows or blocks.

Regards
Faraz
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