The Heart Of The Matter

1
The Heart Of The Matter

• The Java Virtual Machine
• Mike Brunt

2
The Heart Of The Matter - JVM

• What is the JVM?
• Main JVM Suppliers
• ColdFusion and the JVM
• Java J2EE Java EE Servlet Containers
• Where everything sits-fits
• Tuning the JVM
• Metrics Logging
• Using utilities to aid in tuning the JVM
• References
• Summary

3
What is the JVM?

• Sun Microsystems created Java as a high-level
  programming language which should run on as many
  operating systems and hardware variations as
  possible. The goal of write once run anywhere
  meant that a predictable encapsulated operating
  system, no matter what the underlying hardware
  and software, was required.
• The Java Virtual Machine (JVM or JRE) is a
  multi-threaded environment abstracting the actual
  computer operating system from the application
  code.

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Main JVM Suppliers

• These are the main suppliers of Java Virtual
  Machines, there are others.
• Sun Hotspot JVM
• IBM JVM
• BEA JRockit
• MAC OSRuntime for OSX
• Oracle JVM aka JServer OJVM
• Microsoft JVM

5
ColdFusion and the JVM

• Since ColdFusion MX 6.0-6.1, CF has been a Java
  Application which needs what is known as a
  Servlet Container to run on. The most popular
  Servlet Container for ColdFusion is JRun.
• In the Enterprise edition of ColdFusion, the
  actual Servlet Container to be used can be
  selected during the install. In non-Enterprise
  installs JRun is automatically used. The main
  point being that there is always a Servlet
  Container.

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Java J2EE Java EE Servlet Containers

• This is a list 0f Java Servlet Containers which
  are certified as fully J2EE Java EE compliant
  by Sun Microsystems.
• Geronimo from Apache
• JBoss from Red Hat
• JRun from Adobe
• Oracle OC4J
• Sun Java System Application Server (Sun One).
• WebLogic Server from BEA
• WebSphere Server from IBM

7
Where everything sits-fits

• This is a simple diagram showing where the
  Operating System, JVM, Servlet Container and Java
  Application Server sit in relativity.

8
ColdFusion and the JVM

• Standard-Server

• Enterprise

• Windows Install

• Windows Install

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ColdFusion and the JVM

• This is a simple diagram showing where the
  Operating System, JVM, Servlet Container and Java
  Application Server sit in relativity.

10
Tuning the JVM

• Garbage Collectors
• Garbage Collectors (different arguments to
  jvm.config)
• -XXUseParallelGC Use parallel garbage
  collection, this is typically the default
  collector for ColdFusion installations. This
  collector is also referred to as the throughput
  collector. It uses a parallel version of the
  young generation collector. The old (tenured)
  generation is still cleaned with the default
  collector. Note This option can not be used in
  conjunction with -XXUseConcMarkSweepGC.
• -XXUseConcMarkSweepGC Use concurrent garbage
  collection. This collector is also referred to as
  the concurrent low pause collector. It collects
  garbage in the old (tenured) generation
  concurrently to executing the application. Note
  that this option can not be used in conjunction
  with -XXUseParallelGC. Instead you may combine
  it with -XXUseParNewGC
• -XXUseParNewGC Instructs the VM to use a
  parallel collector for the young generation. This
  option can be used in conjunction with
  -XXUseConcMarkSweepGC.
• As a note I have found that using the
  ConcMarkSweepGC along with ParNewGC can cause
  longer Full GCs, I tend to use ParNewGC on its
  own.

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Tuning the JVM

• Full Garbage Collections Minimize
• Sun JVMs use a generational garbage collector
  with two young generations and an old generation.
  New objects are always allocated in the young
  generation part of the heap. Every time the young
  generation is full a minor garbage collection
  takes place. Minor garbage collections don't take
  very long.
• Objects which survived some minor collections,
  because they are still referenced from the
  application, are promoted to the older
  generation. Usually the older generation is full
  at some point too, and needs to be cleaned. This
  leads to a major garbage collection or Full
  Garbage (Full GC) collection that removes garbage
  from both the old and the younger generations.
  Full GCs are stop-the-world events and need to
  occur only when absolutely necessary.

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Tuning the JVM

• Full Garbage Collections Minimize
• One of the first methods I always want to employ
  when troubleshooting is to ascertain how many
  Full GCs are taking place. To do so I add these
  arguments to the jvm.config file, which is
  located in one of these directories depending on
  the installation
• Enterprise drive-volume\jrun4\bin
• Standard/Server - drive-volume\CFusionMX7\runtim
  e\bin
• -XXPrintGCDetails -XXPrintGCTimeStamps
• -XXPrintHeapAtGC -verbosegc -Xloggcyourname.lo
  g
• This will send Garbage collection output to the
  std-out.log and will create a log of all GC
  activity with whatever name you gave yourname in
  either..
• Enterprise drive-volume\jrun4\bin
• Standard/Server - drive-volume\CFusionMX7\runtim
  e\bin

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Tuning the JVM

• Full Garbage Collections Minimize
• Here is an example of the Verbose Garbage
  Collection log output
• par new generation total 97088K, used 0K
  0x10010000, 0x171d0000, 0x171d0000)
• eden space 77696K, 0 used 0x10010000,
  0x10010000, 0x14bf0000)
• from space 19392K, 0 used 0x14bf0000,
  0x14bf0000, 0x15ee0000)
• to space 19392K, 0 used 0x15ee0000,
  0x15ee0000, 0x171d0000)
• tenured generation total 932096K, used 11109K
  0x171d0000, 0x50010000, 0x50010000)
• the space 932096K, 1 used 0x171d0000,
  0x17ca95b8, 0x17ca9600, 0x50010000)
• compacting perm gen total 26624K, used 26606K
  0x50010000, 0x51a10000, 0x58010000)
• the space 26624K, 99 used 0x50010000,
  0x51a0b8a0, 0x51a0ba00, 0x51a10000)
• , 0.1523967 secs
• 3691.704 Full GC Heap before GC
  invocations8
• Heap
• This Full GC was almost certainly unnecessary
  because at the time it ran only 1109k out of
  932096k of the tenured (old) generation had been
  used. I also note the timestamp (3691.704) of
  every Full GC in the log. If I see a regular
  pattern it almost always means something is
  calling a Full GC perhaps using system.gc()

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Tuning the JVM

• Full Garbage Collections Minimize How?
• One pattern I have seen over and over with
  ColdFusion is that Full GCs are very often
  occurring at regular 60 second intervals.
  Although I have never been able to pin this down
  fully, I suspect it is due to a Java process
  called RMI(Remote Method Invocation). So then
  what do we do to control these unnecessary
  stop-the-world Full GCs? There are two
  alternatives
• 1/ Disable Full GCs using the -XXDisableExplici
  tGC jvm.config argument. I am not totally happy
  doing this and in many cases it will not work
• 2/ Run Full GCs at longer regular intervals.
  Applying these arguments instead of
  -XXDisableExplicitGC will cause Full GCs every
  10 minutes (600,000 ms).
• -Dsun.rmi.dgc.client.gcInterval600000-Dsun.rmi.
  dgc.server.gcInterval600000

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Metrics Logging

• I have found that enabling metrics looking is
  invaluable in troubleshooting ColdFusion and JRun
  application issues. Metrics logging will show the
  status of the CF-JRun instance at pre-selected
  time intervals in terms of number of threads in
  use and available memory. In order to enable
  metrics logging we need to edit the jrun.xml
  file, here
• Enterprise install
• drive-volume\JRun4\servers\servername\SERVER-
  INF
• Server-Standard install
• drive-volume
• \CFusionMX7\runtime\servers\servername\SERVER-I
  NF
• Setting detail is on the next slide

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Metrics Logging

• Here is how to enable metrics logging in the
  jrun.xml file
• Firstly uncomment the service class
• Then set metricsEnabled to true, we will leave
  other settings to default.
• Lastly I like to spilt the logs out to make
  reading them easier by this change

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References

• Sun JVM Versions up to 1.5 (5.0)
• http//java.sun.com/j2se/codenames.html
• GC Viewer Tool (Sun JVM up to 1.4x)
• http//www.javaperformancetuning.com/tools/gcview
  er/index.shtml

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Summary

• I have found that the only way to really
  determine the correct garbage collector to use
  for your applications and what the correct
  arguments are to pass to the JVM, via the
  jvm.config file, to effectively manage garbage
  collections is to first determine how many Full
  GCs are occurring and control that if there are
  too many. Then load-test the application whilst
  tuning the arguments passed to the JVM, via the
  jvm.config file.

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The Heart Of The Matter -Presenter

• Mike Brunt
• mbrunt_at_go2ria.net