1. A method of processing a plurality of instances in a federated database, the method comprising: receiving a first transaction request to retrieve data, the request specifying retrieving the data stored according to a range of indices of the federated database, and wherein the federated database comprises a local instance and one or more remote instances; processing the local instance to identify whether data responsive to the request is stored in the local instance; processing each of the remote instances in a predetermined order to retrieve the requested data, wherein the local instance is processed prior to the one or more remote instances, and wherein the processing includes, for each remote instance: comparing a total number of records in a current remote instance being processed to a lower limit and an upper limit of the range of indices, retrieving data from the current remote instance when the lower limit is less than the total number of records in the instances that have been processed, wherein the data is retrieved from the current remote instance using a range of indices specified by the lower limit and a lesser one of the upper limit and the total number of records in the remote instance, and prior to processing a subsequent remote instance identified according to the predetermined order, decrease values of the upper and lower limits when the upper limit is greater than the total number of records in the current remote instance, wherein the decreased values specify an expected range of indices associated with data in the subsequently processed remote instance; and calculating a total number of records in the federated database.