Java Settings

Flags

-Xmx
  Set the maximum heap size. Beware going between 32G and 50G if you have a lot of objects since CompressedOops will not be after 32G.

-XX:+UseG1GC
  It works now for us by default.
  
-XX:+UseStringDeduplication
  This can usefully reduce your footprint if you have a lot of duplicate strings in your application. There is little benefit to
  not enabling it.

-Djdk.xml.entityExpansionLimit=0
  When parsing XML the JVM will go out and try and expand entities like DTDs. You don't want this to happen.

-Dsun.net.inetaddr.ttl=60
  Generally you don't want the default TTL of forever for DNS lookups in production applications.

-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=/mnt/dumps
-XX:ErrorFile=/mnt/dumps/hs_err_pid_%p.log
  If your JVM runs out of memory, rather than just throwing an OOME it instead does a complete heap dump that can be later analyzed
  with jhat to see exactly what was using the heap. Make sure you have at least the max memory size available on disk.

-verbosegc
-XX:+PrintGCDetails
-XX:+PrintGCTimeStamps
-XX:+PrintGCDateStamps
-XX:+PrintTenuringDistribution
-XX:+PrintHeapAtGC
-XX:+PrintStringDeduplicationStatistics
-XX:+UseGCLogFileRotation
-XX:NumberOfGCLogFiles=3 
-XX:GCLogFileSize=10M
-Xloggc:\/mnt\/logs\/${appName}-gc.log
  I heard you were interested in what was going on in GC.

-XX:+OptimizeStringConcat
  Avoids even creating a StringBuilder in many cases. https://groups.google.com/forum/#!topic/jvm-languages/KtVBYfeT83g

-XX:+UseCompressedOops
  With heaps that are less than 32GB, you can save 4 bytes per pointer by enabling this.

-XX:+UnlockDiagnosticVMOptions
-XX:ParGCCardsPerStrideChunk=32768
  Ideal for large heaps.

-XX:+AlwaysPreTouch
  Intializes memory upfront rather than at runtime.

-XX:-OmitStackTraceInFastThrow
  Can be quite painful when debugging. We turn it off.

-XX:+ScavengeBeforeFullGC
  Can improve the performance of a full GC in the sad case that you run one.