The main goal of database security mechanisms is to protect the data stored in the database from unauthorized accesses or malicious actions in general. In fact, several mechanisms needed to detect unauthorized database transactions executed by authorized or unauthorized users have been proposed and/or consolidated in the database arena. Most of these mechanisms can be implemented either externally as an autonomous subsystems separated from the DBMS (sharing the same machine or, preferably, in a dedicated machine), or implemented internally to the DBMS using database triggers. However, in the case of database triggers the performance degradation is expected to be quite high as the execution of database triggers is normally a high resource consuming task. In this paper, a proposed mechanism for
the detection of unauthorized transactions in DBMS is implemented. The proposed mechanism implemented internally to the DBMS using database procedures by compiling them into native code residing in shared libraries. This paper presents a practical example of three mechanisms for detection of malicious transactions in DBMS, the proposed mechanism, internal database triggers, and external procedure. Finally, this paper investigates the performance of the three implemented malicious transactions detection mechanisms in the Oracle 10g DBMS and evaluates the mechanisms using a telephone database. The experimental results showed that the external procedure and the native mechanisms provide the greatest performance gains for computation-intensive procedural operations compared with the database triggers.