c-treeACE SQL Query Performance Improvements

A number of c-treeACE SQL queries were reported to return invalid results, or had performed poorly in testing. The c-treeACE SQL engine was modified with several query optimizations to address these specific cases.

• Missing rows from an outer join. An outer join is converted to an inner join if there is an equality join predicate in an inner join node above any of the right hand side columns of the outer join. An error was found and corrected in forming the execution plan in determining whether a predicate was from the right hand side of the outer join.
• Improved Read Performance. By adjusting the underlying ISAM storage engine key buffering logic, better performance is now obtained with c-treeACE SQL as this avoids updating all ISAM key buffers during a read operation.
• Slow performing Queries. Several reported slow queries have been improved with various optimization enhancements.