Configuration Experiences
What must generally be considered when increasing the allocated RAM for the censhare application Server?
On a basic productive censhare architecture, the java applications censhare Server, WebClient and possibly a local shell Service-Client are running on the same hardware. The (Oracle) database service runs on a separate hardware. The available RAM (swap to disk not included) represents the physical memory limit.
The maximum memory allocated to the JVM size should not exceed the combined memory calculated from all current (Java) processes[1], plus 15-20% buffer for the operating system level. Other non-censhare processes also need to be factored in. In a failover scenario, the takeover of (Oracle) database services should also be taken into account. Failure of doing so may result in an undesirable performance problem when the failover happens.
[1] jps -v | grep -v Jps | awk -F "-Xmx" '{print $ 2}' | awk '{print $ 1}'Note: this article describes the way of increasing the JVM heap size until the available RAM is exhausted. It doesn't cover the initial sizing.
What details must be considered?
Changing the JVM heap memory size requires a restart of the Java application
Minimal (-Xms10g) and maximum (-Xmx10g) value of the JVM heap memory should always be the same. Different values costs JVM performance
Java parameters -Xms and -Xmx needs a unit (e.g. m or g) at the end. If they're not available, the Java application does not start!
The larger the JVM heap memory the longer it takes to perform Full Garbage Collections (time in which the Java application is stopped to clean up memory). Depending on how long a Full Garbage Collection takes this can have a big impact on all connected users
The larger the JVM heap memory the greater will be the size of the heap dump files in ~/css folder (keyword: disk space usage)
The censhare Embedded Database (CDB) Cache is also located within the JVM. The configured JVM heap memory should not be less than the CDB cache size (data cache size + node cache size) + the buffer for other operations within the JVM.
Admin | Status | Overview
When must the heap size be increased?
If you have frequently appearing Full Garbage Collection intervals like the following bad example within ~/work/logs/gc.logNote: Good would be a 'Full GC' every hour with a duration of max. 10 seconds, but it's depending on the system. We have in this example a 'Full GC' every 4 to 5 seconds, having a duration of 3 to 4 seconds, means the system is temporarily freezing. If a user is working at this time on the system he will recognize the freeze. As long as this is not happening all the time until an OutOfMemory error is thrown (possibly a Memory Leak) this is default JVM behaviour.
2012-12-24T11:34:25.213+0000: 2744116.330: [Full GC (System) [PSYoungGen: 29092K->0K(495168K)] [ParOldGen: 5180234K->3606796K(14155776K)] 5209326K->3606796K(14650944K) [PSPermGen: 84517K->84489K(262144K)], 3.2266277 secs] [Times: user=12.55 sys=2.57, real=3.23 secs] 2012-12-24T11:34:29.530+0000: 2744120.646: [Full GC (System) [PSYoungGen: 624K->0K(495168K)] [ParOldGen: 3606796K->3576702K(14155776K)] 3607421K->3576702K(14650944K) [PSPermGen: 84495K->84494K(262144K)], 3.6604210 secs] [Times: user=18.74 sys=0.12, real=3.66 secs] 2012-12-24T11:34:34.224+0000: 2744125.339: [Full GC (System) [PSYoungGen: 320K->0K(495168K)] [ParOldGen: 3576702K->3576667K(14155776K)] 3577022K->3576667K(14650944K) [PSPermGen: 84501K->84498K(262144K)], 4.0962326 secs] [Times: user=18.10 sys=0.11, real=4.10 secs]
Where to configure the heap size and what to consider?
You can configure it within censhare-Admin Client at Configuration | Server | Launcher or directly within the file ~/cscs/app/config/launcher.<server>.xml. This requires an application server (JVM) restart.
Check which java applications are currently running and what heap size they have configured (-Xmx)
jps -v | grep -i CenShareServer
Create a local working copy of the configuration file
cp ~/cscs/app/config/launcher.<server>.xml ~/cscs/app/config/launcher.<server>.xml.saved
Customize and store configuration parameters
vi ~/cscs/app/config/launcher.<server>.xml
Existing values for example such as: <Jvmarg value = "- Xms1536m" enabled = "true" /> <Jvmarg value = "- Xmx1536m" enabled = "true" /> and change it to <Jvmarg value = "- Xms10g" enabled = "true" /> <Jvmarg value = "- Xmx10g" enabled = "true" />
censhare server restart
censhare.rc restart
Check if the reconfiguration of the JVM heap size was successfully
jps -v | grep -i CenShareServer
Troubleshooting
What if I have already increased the heap size but there are still a lot frequent Full GCs and/or OutOfMemory errors?
Ensure that you are using the latest java version (Maybe there's a bug in an older Java(TM) SE Runtime Environment version)
Rethink the relation of the RAM allocation for the running (java) processes
Create a heap dump from the existing situation and check for an OutOfMemory error