Well, baselines are essentially a bunch of hints which determine the
execution plan. Setting the OPTIMIZER_CAPTURE_SQL_PLAN_BASELINES to true
would create a baseline for every single SQL statement executed by a
non-SYS user in the database, including trivialities like 'SELECT
SYSDATE FROM DUAL". There are several logical consequences to that:
* Baseline tables would grow rapidly. The growth would also include
their indexes.
* DBA would not be able to select the baseline for the given SQL
because there would be too many to choose.
* Every time the optimizer decides that it needs to change the plan
for the given SQL, a new baseline will be created. In an inevitable
case that some of the SQL statements with the new baselines are not
performing as expected, the DBA would have to dig deep into the
existing baselines, purge the inadequate ones and create a new one
manually.
If you want your optimizer to adjust more quickly, I would suggest
turning on the adaptive features,
On 3/2/19 6:42 PM, Ls Cheng wrote:
Hi--
Bring this old topic from 2012.
Does anyone actually set OPTIMIZER_CAPTURE_SQL_PLAN_BASELINES to TRUE in production? I have a customer considering it in 12.1.0.2 Exadata but I am not sure if this is good idea because if it is wouldn't this feature on by default?
My personal experience is use this feature for critical, regressed queries only. I also had a couple of customers who set this parameter to TRUE a few years ago and they had production outage due to parsing problems (latch/mutex contention) and the problem didn't go away until they emptied SPM repository, those were 11.2.0.3 databases.
Anything changed?
Thanks
On Mon, Oct 8, 2012 at 7:42 PM Andreas Piesk <a.piesk@xxxxxxx <mailto:a.piesk@xxxxxxx>> wrote:
On 08.10.2012 10:57, Chris Dunscombe wrote:
> Hi,
> We've got a large RAC database where we've been using SPBs for
about 6 months. The SPBs were generated in the perf test
environment and then migrated across. There are still plenty of
SQL statements in live that aren't using SPBs. Now people are
asking about setting
>
> OPTIMIZER_CAPTURE_SQL_PLAN_BASELINES=TRUE
>
> in production, we've run with setting in perf test with full
volume testing and not seen any obvious bad side effects. My
natural reaction is to be cautious and say no.
>
> Am I being sensible, overly cautious or what? Anybody's
experiences in this area would be most welcome.
>
> Version 11.2.0.3 on RHEL 5.6
>
i'm in exactly the same spot and decided against
OPTIMIZER_CAPTURE_SQL_PLAN_BASELINES=TRUE.
my problem with OPTIMIZER_CAPTURE_SQL_PLAN_BASELINES is the
non-existence of any filters. i don't
want baselines for all statements, i want baselines for the
important stuff.
initially i captured the important stuff in STS and loaded these
STS as baselines. after that i
regularly refresh the STS (to capture new statements) and load
them as baselines.
did you noticed occasionally high runtimes for statements covered
by SPBs?
i'm investigating an issue where a simple statement (select a from
b where c=:1) normally returns in
about 10ms but sometimes the reponse time is 1000ms and more. a
testtool running a logical
identical statement not covered by SPBs reports runtimes less than
100ms.
regards,
-ap
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