The Oracle OCI driver is also called the thick driver because of the extensive native code it uses to communicate with the database. OCI is written in C; all of its Java calls use JNI to direct the calls to the C layer. The C layer communicates with the database and returns the results to the Java layer.
The library to map the Java calls to C calls is installed with the Oracle client’s installation. To enable monitoring and recovery persistence with OCI, you must install the Oracle client software.