1. A system, comprising: a multi-system database management system that includes a plurality of database systems with different configurations from each other, and wherein each of the database systems can process data independently by using one or more processors, wherein each of the different configurations at least includes a number of database nodes and a number of access modules in each database node; and an index selection subsystem that includes one or more processors operable to: combine sets of query information from each one of the plurality of database systems into a workload that includes merged query information of the plurality of database systems; generate, from the workload, one or more candidate indexes for each one of the plurality of the database systems; and select one or more recommended indexes from the candidate indexes for each one of the plurality of database systems at least partly based on the configuration of each one of the plurality of database systems, wherein the recommended indexes comprise a first recommended index for a first copy of a given table in the first of the plurality of database systems, and a second recommended index for a second copy of the given table in the second of the plurality of database systems.