Hi Scott,
Which version of the database you are running ?
Why stay away from the baselines where this is the best solution to make
sure a particular SQL will run with a particular plan, this will make sure
it won't piuck up the bad plan anymore. You can also create a baseline with
the "good" from you AWR repository. Indeed you can trace later the CBO to
see why it's always picking up the bad plan.
Regards,
Sve
On Wed, Nov 18, 2015 at 7:58 PM, Deas, Scott <Scott.Deas@xxxxxxx> wrote:
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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