The Oracle optimizer has undergone some major enhancements between Oracle 8.1.7 and 10g, so you may see some changes with respect to how some application SQL executes. Some SQL statements in your applications may run faster, and some may run slower. You should take this opportunity to monitor reports, jobs, etc. that use customized SQL and explain them in the 10g database environment. Optimize them in the non-production environment using production data so that you will be prepared when the upgrade to 10g occurs in the production environment.
Statistics collection in the database has also changed significantly between Oracle8i and 10g. This affects the optimizer which may change SQL execution paths. Review the Oracle Database 10g Release 2 New Features Guide for further information.
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