Re: optimizer parameters

From: Tim Gorman <>
Date: Sun, 24 Apr 2011 11:20:54 -0600
Message-ID: <>


Your instincts are right on -- leave these parameters alone, use system statistics.  Modifying those parameters to fix a localized problem such as a "problem query" is rather like amputating your head because you have acne -- sure it gets rid of the acne but can cause a few other problems.

Suggest to the vendor that they need to solve the specific problem without jeopardizing the rest of the application(s) using the database.  A specific change for a specific problem, not a global change for a specific problem.

On the other hand, we've all been here.  The vendor is likely to dig in their heels, demand that the parameters be changed, ignore your well-reasoned advice, and your management will override you because legal advised them to, and that's that.  Just the way it is... ...can you see that this weekend hasn't been nearly long enough?  :-)

Hope this helps...


On 4/24/2011 6:22 AM, ed lewis wrote:
   I'm curious what other peoples's experience, suggestions
are in regard to the use of the  "optimizer_index_caching", and
"optimizer_index_cost_adj" parameters.
    As a general practice, I leave them at their defaults, unIess
the vendor specifically requires that they be modifed. I  use
system statistics instead. I haven't find the need to do otherwise.
I've tested these parameters on queries, and have received various results.
In some cases, it made use of an index, and in other cases,
it had no impact.
    I'm not a fan of changing this in midstream for an app
that has been running for almost 2 years. This particular vendor
is asking to modify this, as a possible solution to a slow-running
query. I'm pushing back, and would rather address this in other
ways, such as tracing the query, and go from there.
    Your input is appreciated.
solaris 10
rac, asm
-- Received on Sun Apr 24 2011 - 12:20:54 CDT

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