Inter-JVM Sharing

Abstract

SUMMARYSome Java programs lend themselves to being run many times and create the same fixed objects every time. Many of these common objects are Strings. To exploit this trend, we have modified IBM's J9 Java virtual machine (JVM) to allow the same String objects to share (reuse) their internal char[] (character) arrays in each JVM. The first instance of the Java program runs to completion and then sets up the Strings for sharing, so that subsequent instances of the same program can use the char[] arrays that it created instead of recreating them. String sharing will not provide benefit in all applications, but for those that fit the pattern, as exemplified by the Eclipse and H2 benchmarks, we were able to achieve significant heap saving with negligible impact on performance.