Adaptive Server version 15.0 includes substantive changes to the query processor. For most customers, the new query processor provides a faster and more efficient environment. However, you may have tuned your server and applications based on the more restricted query processor from Adaptive Server version 12.5.4 and earlier and find the benefits of the version 15.0 query processor unsuitable in some situations. In that case, use the compatibility mode to upgrade to Adaptive Server 15.0 from version 12.5.x but retain performance characteristics similar to version 12.5.x. When you enable compatibility mode, Adaptive Server 15.0 uses a query engine similar to the one used in version 12.5.4, and provides an alternative optimization and execution strategy.
