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Optimizer_max_permutations Becomes Hidden Parameter in Oracle10g
May 3, 2004

 Starting in Oracle10g, the parameter optimizer_max_permutations parameters becomes a hidden parameter, starting with an underscore as _optimizer_max_permutations with a default values of 2,000.  Now, all table evaluations limits are hidden parms, just like _optimizer_search_limit became a hidden parameter in Oracle 8.1.7.
 
The _optimizer_search_limit and _optimizer_max_permutations parameters work together, and the optimizer will generate possible table joins permutations until the value specified by _optimizer_search_limit or _optimizer_max_permutations is exceeded. When the optimizer stops evaluating table join combinations, it will choose the combination with the lowest cost. For example, queries joining nine tables together will exceed the optimizer_search_limit but still may spend expensive time attempting to evaluate all 362,880 possible table join orders (nine factorial) until the optimizer_max_permutations parameter has exceeded its default limit of 80,000 table join orders.
 
For more information, see my article here:
 
 

 

 

  
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