1. A compute node capable of optimizing just-in-time (‘JIT’) compiling for a software application, the compute node having installed upon it a software Virtual Machine (‘VM’) capable of supporting the software application, the compute node comprising a computer processor and computer memory operatively coupled to the computer processor, the computer memory for the compute node having disposed within it computer program instructions that when executed by the computer processor cause the computer node to carry out the steps of: identifying a plurality of portions within the software application; for each portion of the plurality of portions, assigning, by an application manager, one of a plurality of a JIT levels to the portion of the software application, wherein the plurality of JIT levels excludes a level in which no JIT compiling is carried out, including: establishing the JIT level for the portion of the software application in dependence upon both a historic JIT profile for the portion of the software application specifying, for each previous execution, one of a plurality of JIT levels previously used when jitting the portion of the software application and previous execution performance of the portion of the software application including a previous performance value and a number of times the particular portion was invoked; wherein each portion of the plurality of portions of the application is assigned a different JIT level; and jitting, by the VM installed on the compute node, the portion of the software application in dependence upon the JIT level assigned to that portion of the software application.