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Pl post details of OS versions, exact database versions (to 4 digits) and init.ora parameters of the 10g and 11g databases. Have statistics been gathered after the upgrade ?
For posting tuning requests, pl see these threads
HOW TO: Post a SQL statement tuning request - template posting
When your query takes too long ...
Pl see if the SQL Performance Analyzer can help - MOS Doc 562899.1 (TESTING SQL PERFORMANCE IMPACT OF AN ORACLE 9i TO ORACLE DATABASE 10g RELEASE 2 UPGRADE WITH SQL PERFORMANCE ANALYZER)
HTH
Srini
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