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
a really good post at:
https://oraganism.wordpress.com/2009/07/21/when-to-gather-fixed-object-optimiser-statistics/
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