Debugging User-Defined Functions in RDBMS Client-Server Environment

Abstract

Many relational database systems offer a User-Defined Function (UDF) facility which allows the user to extend the intrinsic functionality of SQL expressions with their own functions written in languages such as C and C++. UDF modules are installed on the database server where they run under a daemon process managed by the DBMS. Normal debugging techniques fail with UDF in the server runtime environment because client cannot readily communicate with UDF, which runs as an asynchronous, remote, privileged process from the client’s point of view. Developing and testing non-trivial UDF modules may not be viable without a ready means to debug in this environment. In this paper we explore the factors that inhibit UDF debugging. We then present an idea that overcomes these obstacles and develop two variations of this idea. The self-initiated approach can be intexpensively applied by modification of the UDF code. We demonstrate a simple implementation of this technique which was experimented with using IBM’s DB2/Common Server relational database. The DBMS-initiated approach has DBMS managing the debugger invocation, with control provided through SQL language extensions, to make debugging more convenient and flexible for the developer of UDF. Both approaches allow normal debugging of UDF in client-server encironment esing ordinary debuggers.