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Reducing latency with Sun Real Time JVM

Posted 22 December 2008 @ 12:34 am by Nati Shalom

Frederic Pariente Engineering Manager at Sun Microsystems posted an interesting summary of a case study with GigaSpaces on Sun blog: Gigaspaces curbs latency outliers with Java Real Time

In the context of a customer proof-of-concept this summer and in the light of the 2.0 release of Java Real Time System --JRTS 1.0 had the bad prerequisite of source code changes--, Gigaspaces revisited the opportunity for Java Real Time to serve the low-latency requirements of trading applications. Gigaspaces XAP 6.5, Solaris 10 and both Java 5.0 standard and real-time JVMs were used for the benchmark. The test scenario included a trade matching engine and multiple clients injecting messages at extreme speed. The success criteria was to get guaranteed latency per message under 10 msec, with no code modification to the matching engine"

"..The first lesson learned was that msec latency was achievable with the standard JVM, through some advanced tuning of the JVM command-line options. While the customer had reported application freezes up to 20 sec during garbage collection under heavy load --he was running the JVM with no particular flags, unfortunately default JVM options optimize for throughput--, latencies could be brought down to milliseconds by switching to the Concurrent Garbarge Collector"

"..The second lesson learned was that the number of outliers can be reduced by an order of magnitude by using the real-time JVM. At a small cost in terms of application throughput --lower-- and CPU usage --higher-- of course"

You can see the full detailed benchmark and JVM option in the original post.

How Real Time JVM works?

For those who are not faimiliare with Real Time JVM, Fredric points to a very detailed presentation on his post Java Real Time for latency-critical banking applications which I'd recommend looking at. I took one slide from the presentation which i found useful for understanding the general concept behind Real Time VM.

As could be seen in the above diagram the RT-JVM introduces new type of threads "Critical RT threads". It makes sure that GC will not run while those thread are running and in that case provide better predictable behavior.