RE: Changed execution plans..

Tim,

Thanks for your thoughts. I'm thinking that the import and the resulting changes is likely the issue.

RF

Robert G. Freeman
Technical Management Consultant
TUSC - The Oracle Experts www.tusc.com
904.708.5076 Cell (it's everywhere that I am!) Author of several books you can find on Amazon.com!

-----Original Message-----
Sent: Monday, January 20, 2003 8:44 AM
To: Multiple recipients of list ORACLE-L

Robert,

Just thought I'd ask, since it hasn't been mentioned in the thread previously, but...

        ...has query performance worsened or improved, or is any change unnoticeable? What is the before- and after-readings for elapsed time?

After all, if the rows are packed more "densely" into the blocks, then perhaps an FTS is not such a bad plan...

Also, don't forget that the import may have changed the physical order of the rows in the table, so now the "clustering factor" of the various indexes may have changed enough to the point where the CBO (correctly!) decided that using the index for a RANGE SCAN may not be optimal. Since CLUFAC is judged on a scale between the DBA_TABLES.BLOCKS and DBA_TABLES.NUM_ROWS, even a CLUFAC which hasn't changed much (due to the table being reimported with rows in the same physical order) would still be greatly affected by a change in DBA_TABLES.BLOCKS...

Thanks!

-Tim

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Sunday, January 19, 2003 9:28 PM

> Thanks Cary... I've actually considered most of those already. This isn't
my
> database, I'm coming in to help someone else. In this case, the database
> schema was accidentally dropped, and recovered from an export. I'm
wondering
> if the import might have created blocks that are packed more densely and
> that this might be the cause of the problem. I'm told the parameters are
the
> same, that the physical structure is the same, they are not using stored
> outlines and the SQL has not been changed. No patches have been applied,
so
> it's apples for apples with the exception of the statistics and, possibly,
> the data density. They have some old stored statistics that they generated
> pre-schema drop that they are supposed to send me, so I'm going to look at
> that tomorrow and run a 10053 trace on one of the changed queries and see
> what I can find. I was just wondering if I could be missing something
> obvious..... Seems like that is just the way, it's the obvious things that
> get missed... :-)
>
> Thanks so much for your comments!
>
> RF
>
> -----Original Message-----
> Millsap
> Sent: Sunday, January 19, 2003 8:54 PM
> To: Multiple recipients of list ORACLE-L
>
>
> Robert,
>
> Seven reasons I can think of include changes to:
>
> 1. Oracle instance parameter values (changes when you edit the
> parameters, whether in the stored "init.ora" way, or via ALTER SYSTEM or
> ALTER SESSION commands)
> 2. Database table and index statistics (changes, e.g., when you run
> dbms_stats.gather_database_stats)
> 3. System CPU and I/O statistics (changes, e.g., when you run
> dbms_stats.gather_system_stats)
> 4. Database schema configuration (changes when you create/drop indexes,
> etc.)
> 5. Stored outlines (changes when you create or reassign outlines)
> 6. SQL text (changes when you manipulate the application SQL)
> 7. Oracle query cost model (changes when you upgrade or patch your
> Oracle kernel)
>
>
> Cary Millsap
> Hotsos Enterprises, Ltd.
> http://www.hotsos.com
>
> Upcoming events:
> - 2003 Hotsos Symposium, Feb 9-12 Dallas
> - RMOUG Training Days 2003, Mar 5-6 Denver
> - Hotsos Clinic 101, Mar 26-28 London
>
>
> -----Original Message-----
> Freeman
> Sent: Sunday, January 19, 2003 1:24 AM
> To: Multiple recipients of list ORACLE-L
>
> Hey Ya'all... (still got my southern roots even up here in Chicago!)
>
> Anyone want to throw in some possible reasons why an execution plan
> might
> change for a given table query....This is on Oracle9iR2 on SUN. I've
> looked
> at the obvious causes:
>
> 1. Object has changed - Appears not to have changed.
> 2. Database parameters have changed - Appears that no parameters have
> changed.
> 3. Statistics (data volumes, distribution, cardinality, etc) have
> changed -
> Still looking into this, but the volumes have not changed dramatically
> even
> if they have changed.
> 4. Other physical database changes.
>
> None of these seem to apply. I've got a database that a few weeks ago
> were
> doing indexed
> lookups using a partitioned index on a partitioned table. Now, it seems
> that
> these queries
> are doing full table scans on this partitioned table. I'm still
> gathering up
> the details for the items above (e.g how much have the objects changed)
> and
> I'll probably run a 10053 trace on one of the bad queries to see what
> the
> optimizer is doing on Monday, but I'd like to just poll for some
> additional
> ideas. I *AM* getting partition elimination (thank goodness) but I've
> got
> two FTS on one partition of this table that are just killing it. They
> want
> to quantify the reason why this access has changed so I'm trying to
> think of
> what kinds of stuff I can look at to try to do this.
>
> I will add that this table was just rebuilt recently (through
> imp/exp)...
> can the change in row to block density make the difference.... hmmmm....
>
> Any ideas??
>
> RF
>
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> Author: Robert Freeman
> INET: robertgfreeman_at_yahoo.com
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