JIT

Starting with Oracle 11gR1 Oracle JVM includes Just-in-Time compiler. Its goal is to convert JVM bytecode into platform-specific native code based on the performance data gathered in run-time. It is stated in the documentation that JIT “enables much faster execution” – and this is, in general, true. There are ways to control the behavior of JIT, one way is described in the MOS Doc ID 1309858.1, and another one here.

JNI in Oracle

JNI – Java Native Interface – is an interface for cooperating Java and legacy code. Oracle RDBMS doesn’t support it officially in embedded Oracle JVM (aka “Aurora”):

Oracle Database does not support the use of JNI in Java applications. If you use JNI, then your application is not 100 percent pure Java and the native methods require porting between platforms. Native methods can cause server failure, violate security, and corrupt data.

All true – and nevertheless it’s working.