Data synchronization includes receiving an update request from a client system for a first record set, wherein the update request includes search criteria used to initially determine the first record set and hash summaries of records of the first record set, and searching a data storage device for records matching the search criteria. The searching generates a second record set of records having hash summaries. Record identifiers of records of the second record set may be compared with record identifiers of the hash summaries of the first record set. Responsive to determining that a record identifier of a selected hash summary of the first record set matches a record identifier of a record of the second record set, a determination may be made whether hash fields of the selected hash summaries mismatch and, responsive to determining a mismatch between hash fields, a field of the record of the second record set represented by the mismatched hash fields may be sent to the client system without sending fields of record determined to match.