Java Performance Tuning

Clustering Objects and Counting I/O Operations

Clustering is a technique that takes advantage of locality (usually on the disk) to improve performance. It is useful when you have objects stored on disk and can arrange where objects are in reference to each other. For example, suppose you store serialized objects on disk, but need to have fast access to some of these objects. The most basic example of clustering is arranging the serialization of the objects in such a way as to selectively deserialize them to get exactly the subset of objects you need, in as few disk accesses, file openings, and object deserializations as possible.

Suppose you want to serialize a table of objects. Perhaps they cannot all fit into memory at the same time, or they are persistent, or there are other reasons for serialization. It may be that of the objects in the table, 10% are accessed frequently, while the other 90% are only infrequently accessed and the application can accept slight delays on accessing these less frequently required objects. In this scenario, rather than serializing the whole table, you may be better off serializing the 10% of frequently used objects into one file (which can be deserialized in one long call), and the other 90% into one or more other files with an object table index allowing individual objects to be read in as needed.

Alternatively, it may be that objects are grouped in some way in your application so that whenever one of the table objects is referenced, this also ...