How Index Access Paths Can Change Without New Statistics
In a production environment, an execution path for queries often changes, even in the absence of any related changes. You confirm that no new statistics were collected (in fact, you might even have locked the statistics to prevent changes in execution plans). Prior to Oracle Database 11g and the cardinality feedback feature and automatic query tuning capabilities, if nothing truly changed (i.e. stats, instance parameters, etc.), and something such as bind peeking with histograms present wasn't in play, then plans pretty much stayed the same. However, even if you're absolutely positive that the optimizer shouldn't change any execution plans, it does. How's this possible? Well, most databases ...
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