Understanding Optimizer Statistics
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An Oracle White Paper
January 2012
Understanding Optimizer Statistics
Understanding Optimizer Statistics
Introduction ....................................................................................... 1
What are Optimizer Statistics? .......................................................... 2
Table and Column Statistics .......................................................... 2
Additional column statistics ............................................................ 3
Index Statistics ............................................................................ 10
Gathering Statistics ......................................................................... 11
GATHER_TABLE_STATS ........................................................... 11
Changing the default value for the parameters in
DBMS_STATS.GATHER_*_STATS ............................................ 13
Automatic Statistics Gathering Job .............................................. 15
Improving the efficiency of Gathering Statistics ............................... 18
Concurrent Statistic gathering...................................................... 18
Gathering Statistics on Partitioned tables .................................... 20
Managing statistics .......................................................................... 22
Restoring Statistics ...................................................................... 22
Pending Statistics ........................................................................ 23
Exporting / Importing Statistics .................................................... 23
Copying Partition Statistics .......................................................... 25
Comparing Statistics .................................................................... 26
Locking Statistics ......................................................................... 27
Manually setting Statistics ........................................................... 29
Other Types of Statistics ................................................................. 29
Dynamic Sampling ....................................................................... 29
System statistics .......................................................................... 31
Statistics on Dictionary Tables ..................................................... 32
Statistics on Fixed Objects .......................................................... 32
Conclusion ...................................................................................... 33
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