Agblad Tore wrote: > Check HEAP size for the zLinux server, does it really need 6 GB ? > A big heapsize causes Garbage Collection to take long time, so it's important > to tune that HEAP size right.
This is an extreme oversimplification. With a 1.3 JVM or an old non-parallel GC algorithm on newer JVMs the behaviour for large heaps is what you describe. Using any modern JVM (1.5 or 1.6) and an appropriate parallel GC policy a large heap is unlikely to cause a performance penalty. Having spent some time recently looking into precisely this pain, I suggest your starting point is to ensure you aren't either paging at the zVM layer or swapping the JVM. Assuming those things are true you need to start doing verbose GC logging and dumping into, e.g., the pmat tool (http://www.alphaworks.ibm.com/tech/pmat) in order to understand what your JVM is doing with GC. Another tool we've found invaluable is JInsightLive (http://www.alphaworks.ibm.com/tech/jinsightlive), which is one of the few profiler tools for Java on Z, and will give you a detailed breakdown of where your code is spending its time (amongst other things). Obviously profiling tools are subject to the usual caveats re: accuracy of reporting in a virtualised environment, but these are a good starting point. ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
