Hi,
Using 11.2.0.3 version.
We have some sql which been no change to and no material changes in data volumes previously - sql concerned would run in under 20 secs and used an available index.
Today took over 2 hours - due to index not being used.
When put a hint in to use that index, performance back to normal.
Why would ORACLE decide to replace a plan which took secs with one that took hours?
Thought would never decide to replace one so and wonder if possible to configure something at database level to never replace a plan which so massively inferiror.
Thanks