OpenSolaris uses a single-threaded malloc by default for all applications. The JDK that is compiled for Solaris fails to be linked against mtmalloc or the newer umem malloc implementation that is multithread optimized. In a multithreaded application using a single threaded malloc can degrade performance. As memory is being allocated concurrently in multiple threads, all the threads must wait in a queue while malloc() handles one request at a time, this is called heap contention. To get around this contention point you can force the JDK to use the umem malloc. 

LD_PRELOAD=/usr/lib/libumem.so /opt/jdk1.7.0/bin/java start.jar or LD_PRELOAD=/usr/lib/libmtmalloc.so /opt/jdk1.7.0/bin/java start.jar

This simple fix has really improved performance on our web service fabulously40. The application went from serving 120req/sec uncached to 170req/sec. Not bad no? 

This also works wonders for mysql and varnish, two applications that really put those threads to use.  We have dropped 100ms in response time with varnish by just using umem for the malloc implementation.