4. A computer system as claimed in claim 1 further comprising a version indicator stored at the OLTP database server and indicating last completed synchronization between the OLTP database server and the OLAP database server.
5. A computer system as claimed in claim 4 wherein the OLTP application server copies the version indicator into a session state of the client application, and the client application redirects the query to the OLAP database server when the version indicator stored at the OLTP database server has changed relative to the copy of the version indicator in the client application.