Network Performance

A common criticism of Java applications is that they are "too slow". The often-quoted figure is "20 to 40 times" slower than equivalent compiled C or C++ applications. However, it is strongly associated with networks and in a network context Java applications suffer zero speed penalty. In just the last 10 years CPU speed has increased tenfold, yet the speed of network access through modems has barely doubled and many of us are still using the same 10 Mb/sec Ethernets we were using 10 years ago (though now switched). The consequence of this is that machines are much faster than the networks they communicate with. Java applications that make use of the network spend most of their runtime waiting for the network.

The NFS client uses several techniques to use the network efficiently. First it caches NFS file attributes and data in memory to avoid unnecessary calls to the server. When the client connects to an NFS version 3 server it eliminates the 8k read and write limitation of version 2 and reads or writes data in large 32k blocks. Version 3 also allows the client to use safe, asynchronous writes that are several times faster than the synchronous writes required by version 2. Finally, the NFS client utilizes Java threads to implement read-ahead and write-behind. If the client detects that the application is reading a file sequentially then it will asynchronously issue read requests ahead of the current block of data in anticipation of the application's need. The use of a single block read-ahead can double the client's file reading throughput. Similarly, write-behind allows the client application to write blocks of data to the server without waiting for confirmation for each block of data. This has a similar effect on file write throughput.

Our experience with the NFS client is that it can read and write data at over 1 MB per second across a 10Mb Ethernet from a Sun Ultra 1 client.