Why Plans Change

Cause	Description
Stats changed	Table, index, or column stats were refreshed. Cardinality estimates changed.
Bind peeking	The first bind value caused a plan that’s bad for later values.
No histograms	Optimizer assumes uniform data when actual data is skewed.
New index or object	The optimizer sees a new access path and tries it.
Adaptive optimization	Oracle switched plans mid-execution based on early row counts.
SQL text changed slightly	Even whitespace differences result in new SQL_IDs and plans.
Cursor aged out	The plan aged out of the shared pool and was regenerated.