Hi Matt,
I’m not sure about the method changing from patch to patch but it certainly
changed in 11g. Have a read of
https://blogs.oracle.com/optimizer/how-does-autosamplesize-work-in-oracle-database-11g
There’s a link too for the 12c version.
In summary: yes, it will be sampling every row for some things. No, that
should not actually give you a problem - memory usage is still quite low
and the full scan of the table itself shouldn’t really take that long.
Of course, if you are manually gathering statistics every day during
business hours then you may be more effected than if you are just letting
the automatic task take care of one or two stale tables each night.
The cascade option you are using will mean that indexes will have their
statistics regathered each time too, this could easily add up.
If you are having trouble gathering statistics due to time constraints, the
flavour of the month problem is incremental statistics.
Hope that helps,
Andrew
