All,
We have an environment that has been experiencing some wandering plans. While
we'd like to look into the details to see why the optimizer is choosing bad
plans, we have immediate needs to get statements running with good plans that
have been used in the past. When we're contacted in time, we have been
stopping the query, flushing the plan from the shared pool (using
DBMS_SHARED_POOL.PURGE), gathering stats (where applicable) and re-running.
The problem is that sometimes we're not contacted until the statement has been
running for so long that it's now showing up in dba_hist_sql_plan, meaning the
DBMS_SHARED_POOL.PURGE procedure will no longer flush it as an available plan
for the optimizer.
We have tried setting baselines for these statements (although we'd prefer not
to use them long term), but the optimizer continues to see these bad plans as
cheaper options that would be a better choice.
Is there a way to completely eliminate or invalidate a past plan from being
considered by the optimizer again?
Thanks,
Scott
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