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Don Burleson Blog 







optimizer_adaptive_features  tips

Oracle Database Tips by Donald BurlesonJanuary 29, 2015

How do I use the optimizer_adaptive_features parameter?


Answer: Oracle notes that optimizer_adaptive_features enables or disables all of the adaptive optimizer features, including adaptive plan (adaptive join methods and bitmap plans), automatic re-optimization, SQL plan directives, and adaptive distribution methods.


The optimizer_adaptive_features parameter is part of the Oracle12c adaptive execution plans are a add-on to Oracle dynamic sampling, a new feature of dynamic statistics.

Also see Oracle 12c adaptive optimization of SQL.

Oracle is striving to get over an ongoing issue with always having enough detail in the metadata to always choose the "best" execution plan, and Oracle is now working towards an adaptive, "self-learning" optimizer.

In this new approach, "real-time" statistics collection is done at query execution time, and the optimizer has the option of changing a tables join methods between a hash join to a nested loops join, well after the original plan was generated!

Join statistics are now monitored for executing SQL statements and a new v$sql column is_reoptimizable has been added to indicate when a query will benefit from dynamic statistics.

This funky new functionality is controlled by the parameters optimizer_adaptive_reporting_only and  optimizer_adaptive_features and optimizer_adaptive_ plans.  This can also be used a hint in a query: with the opt_param directive

select /*+ OPT_PARAM('_optimizer_adaptive_plans','true') */

See my notes on adaptive execution plans and 12c adaptive SQL optimization.


Also see my bind_aware hint tips.

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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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