Compare the index selectivity and IO projections from the 300-series trace flags in the 12.x Adaptive Servers with show option output in the 15.x Adaptive Server. Some possible causes of optimizer differences include:
Data and data distribution problems. Check data layout and verify that these match the production system.
Index definitions. Verify that your reindexing scripts worked. Using sp_helpindex, compare the index definitions of the production and test systems.
Resolve any problems before continuing.
If you captured abstract plans in the previous release of Adaptive Server, use the query metrics feature to compare plans and performance on the new version. See the “Query Processing Metrics” chapter in the Query Processor manual at http://sybooks.sybase.com/as.html for details.
