10.2.0.4 vs 10.2.0.5 SQL optimizer

Question

Hello,
Recently we upgraded from Oracle 10.2.0.4 to 10.2.0.5 deployed on AIX 5. Immediately we could see slowness for a particular SQL which used partition as well as indexed column in predicate clause.
e.g.
SELECT COL1, COL2
FROM TAB1 PARTITION (P1)
WHERE TAB1.COL3 = 123;
There is an index created on COL3. However explain plan for this SQL showed that this index was not getting used. Surprisingly, when we removed partition from SQL, itused the index
SELECT COL1, COL2
FROM TAB1
WHERE TAB1.COL3 = 123;
There is one more observation - When we reverted back to 10.2.0.4 optimization strategy on Oracle 10.2.0.5. The original SQL that had partition clause used the index as it should have been and explain plan matched to what was before the Oracle upgrade.
I have few questions based on these observations. Any help will be appreciated.
1. Are there any changes in the 10.2.0.5 optimizer that is making SQL becoming slow?
2. Is there any problem in SQL that is making it slow?
3. I believe moving to 10.2.0.4 optmizer on Oracle 10.2.0.5 is a short-term solution. Is there any permanent fix to this problem?
4. Does Oracle 11g support 10.2.0.4 optimizer?
Please let me know if more details are needed.
Thank you!

Answer 1

Have statistics been gathered after the upgrade ? Has the OPTIMIZER_FEATURES_ENABLE init.ora parameter been set to 10.2.0.5 after the upgrade ?
http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/initparams142.htm#CHDFABEF
Pl post the explain plans for the statement in both 10.2.0.4 and 10.2.0.5 following the instructions in this thread - HOW TO: Post a SQL statement tuning request - template posting
Every upgrade/patch can introduce changes in the optimizer. You can use 10.2.0.4 features in 11g using the parameter mentioned above - but why would you want to do that ?
HTH
Srini