| statistics collection [message #512137] |
Fri, 17 June 2011 02:47  |
Its_me_ved
Messages: 979
Registered: October 2009
Location: India
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Senior Member |
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We collected statistics including histograms on some tables.But after that statistics were gathered
again on the schema.Does the new stats can overwrite the statistics for the tables for which histograms were gathered?
Regards
Ved
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| Re: statistics collection [message #512378 is a reply to message #512137] |
Sun, 19 June 2011 21:58  |
hkchital
Messages: 128
Registered: September 2008
Location: Singapore
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Senior Member |
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Yes, possibly.
Both gather statistics runs would have been using the same interface. : DBMS_STATS GATHER_TABLE_STATS or GATHER_SCHEMA_STATS.
Method_Opt enables gathering of histograms.
If you explicitly specify Method_Opt ("for .. columns ... size ..."), Oracle uses the specification.
If you do not specify Method_Opt, Oracle may default to "for all columns size auto") which may drive collection of histograms on some columms but not on others -- it depends on the column usage information that Oracle uses to determine the "SIZE AUTO".
If you want specific histograms, always be careful to ensure that you include the specification.
If you are comfortable with the automatic histograms, you can rely on the auto behaviour.
Note that the "default" Method_Opt can also be overriden with DBMS_STATS.SET_PARAM.
Hemant K Chitale
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