A JDK bug (See: https://jdk6.dev.java.net/issues/show_bug.cgi?id=23) in JDK6 Sun PKCS11 Provider could cause an OutOfMemoryError when running certain SSL scenarios under heavy stress.
If you run into this issue, remove sun.security.pkcs11.SunPKCS11 provider from the java.security file in your JRE installation.