https://blogs.oracle.com/optimizer/entry/what_s_new_in_12c

and I quote:

If we detect during execution that the optimizer’s cardinality estimates were wrong, then some plan choices can be changed “on the fly” to better options. While we can’t completely change the plan during execution, there are certain local decisions that can be changed, like join method

To summarize the excellent asktom article here, yes, if a query block is going to return one row, then it’s ok, in fact, the mechanism for doing a cartesian join (on that single-row query) is fairly efficient, and that’s why the optimizer chooses it.

http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:4105951726381

 

Insert APPEND and PARALLEL hints invoke DIRECT PATH (adding new blocks above High Water Mark)

==>> no UNDO/Rollback

There is, however, no effect on REDO.

To stop REDO (almost), alter table NOLOGGING

https://forums.oracle.com/forums/thread.jspa?threadID=664885&start=15&tstart=0

http://kerryosborne.oracle-guy.com/papers/Controlling%20Execution%20Plans.pdf

a really good post at:

https://oraganism.wordpress.com/2009/07/21/when-to-gather-fixed-object-optimiser-statistics/

 

 

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