Methods, computer program products, and systems are presented. The method computer program products, and systems can include, for instance: examining data of breaches of a geofence by client computer devices to determine respective positions of the breaches; receiving by a database system transaction data from client computer devices, the transaction data defined by insert query data; changing a structure of an index of a certain table of the database system in response to the receiving; generating logging data in response to the receiving of the transaction data; providing using the logging data prediction specifying data, the prediction specifying data specifying one or more change predicted to occur with respect to the index; and modifying the index in dependence on the prediction specifying data.