Topic: SQL*Plus and PL/SQL >> USER_TAB_HISTOGRAMS use for analysis...
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| Title: USER_TAB_HISTOGRAMS use for analysis... |
| Yogesh |
Posted: Dec 21, 2005 10:15:48 PM |
Total Post: 10
Joined: Dec, 2005
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How the USER_TAB_HISTOGRAMS improve the analysis used by the cost-based optimizer?
Regards. |
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 Vigyan |
| Posted: Dec 22, 2005 10:07:30 PM |  |
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Total Post: 387
Joined: May, 2001
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You can query this view to see the Histograms. Be careful when using histograms. Column histograms should be created only when you have highly-skewed values in a column.
Histograms affect performance and should only be used when they are required for a faster CBO execution plan. They incur additional overhead during the parsing phase of an SQL query. Histograms can be used effectively only when
- A table column is referenced in one or more queries
- A column's values cause the CBO to make an incorrect guess
- Significant skewing exists in the distribution of a column's data values
Hope it helps.
Vigyan
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