In the area Index à window Admin you can manually integrate the delta index in the main index by choosing Merge Delta Index(function key or context menu).
Using the delta index speeds up the update of the index as long as the delta index is small. If it becomes too large, you have to integrate it into the main index. TREX then creates a new delta index after this integration.
For detailed information on the delta index and its integration, seeDelta Index Configuration.