JIT Compiler: Configuration and Statistics 

Use

This part of the navigation structure in the VMC System Administration (transaction SM53) provides configuration and statistical information about the Just-In-Time Compiler of the SAP VM Container.

Features

The navigation structure in SM53 contains the JIT Compiler subnodes - configuration, code cache, non-compilable methods, and statistics.

You can only use monitoring here; the configuration of the JIT Compiler cannot be changed in the VMC system administration.

Configuration

You can see all the parameters that control the behavior of the JIT Compiler in a table. For each parameter the table has the following entries:

●      Name of JIT parameter

●      Predefined Value: Each parameter has a predefined value (default value, factory setting), which is displayed in this column. <unset> (=undefined) is considered as a presetting too in this context.

●      Current Value: The predefined values can be changed in profile parameters when the VM is started. This column tells you what the values on the parameters currently are. The values of the subparameters for "excludeFile" and "methodtraceFile" are determined indirectly from the associated control file.

If you want to change these profile parameters, you have to change the profile file of the instance and start the VM Container on this instance (transaction SM52, VMC → Reset, see Functions for the VM Container (Menu VMC)).

For information about the most important JIT parameters vmcj/option/jit/compile see Configuration Parameters.

Code Cache

Java methods are translated by the JIT Compiler into a sequence of machine commands that can be executed directly on the hardware. The results of the translation are stored in the code cache, where they can be called and used time and time again. Whether the generated code can be used by multiple VMs at the same time (tab page, Jointly Used Code Cache), or whether each VM has to generate its own copy of the machine code (tab page, Local Code Cache), depends on the properties of the translated methods.

The list displays the information below for each translated method (column, Method Name):

●      Size [Bytes}: Space occupied by the generated machine commands (including constants) in the code cache.

●      Class Loader Name: Name of the class loader that loaded the method.

●      Start Address: Start of the code cache area for the translated method. This address is not necessarily the address the caller uses.

●      End Address: End of the code cache area for the translated method.

 Non-Compilable Methods

There are various circumstance where a method cannot be successfully translated by the JIT Compiler. The most likely case is that the maximum permitted size of the code cache has been exceeded due to a Java method that is too complex. The method name and the associated class loader is displayed in the list. Methods in Local Classes are different to Methods in Shared Classes here too (different tab pages).

Statistics

All the internal statistical information about the JIT Compiler is displayed under Statistics.

The information is mainly for SAP Support to help with analyzing problems, and is not documented in detail.

The table contains the following columns:

●      Name of the Statistical Record Field.

●      Field Type: A statistical record field can have the type "counter" (field type times), "time difference" (field type us, unit microseconds), "length" (field type bytes) or "name" (field type method).

●      Total Value of the Statistical Record Field: Sum of the field values across all statistical records

●      Last Request: Field value of the processing just finished

●      Current Request: Field value at the time of compiling the list. This value is not necessarily the same as the field value at the end of the processing.