Simon Riggs wrote
> ISTM we need a way to say "this query's parameters vary wildly at
> execution time, so I really need to re-plan it every time".
If the wild variations don't affect the cost estimate, they won't affect the plan?
Isn't it more a case of
"even a minor variation in just one of this query's parameters can result in wildly different cost estimate,
so I really need to re-plan it every time."
This is something that the database may be able to determine from currently collected statistics.
However I suspect that any means of trying to automatically determine that would *always* result in
"Yep, minor changes can wildly affect the cost estimate"
(I'm ignorant of details and history but...)
Could this be added (conditionally):
With the stored plan, store the cost estimate,
Re-estimate the cost of the chosen plan with the newly supplied parameters,
If the new cost is significantly higher then re-plan.
Checking the cost of a plan every time should be a lot cheaper than always re-planning.
I can already see problems with this...
the query will get slower and slower over time as it settles onto the plan that best handles the worst cases.
Stephen Denne.
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