When Concurrency Increases?• Throughput increases, but where will it stop?• When there are contention for the server• Contention for what? o CPU o Memory o Disk - I/O o Network -I/O• If your server running on full capacity, there should be at least one resource under contention.
How to measure Contention?• CPU - CPU or load average• Memory - GC logs, monitor memory, sometime swapping• Disk I/O - IOPS per seconds, load average• Network I/O - network utilization, load average• What is load average? length of processor queue of the OS• How much load average is too much? o Load average = number of cores (machine is fully used) o Load average = 2* number of cores (machine is loaded)
If you cannot find contention• Either load is too small• You have too much locks. Look for lock profile• Server might be processing with too less threads (IO and CPU thread switches)
Performance Tuning• Increase throughput/ latency or both• Know that latency vs. throughput is often a tradeoff• Run the system and see how it does, make sure you are putting in enough load• Verify where is the bottleneck? is it CPU, memory, network, or disk• Start tuning
Tuning• When you tune, bottlenecks will shift, you will have to shift your focus• Can you tune settings (Application, JVM, OS) to improve and shift the bottleneck? play with parameters .. we call this parameter sweep• Then focus on the code, look for right profile o CPU profile o Memory/ Allocation profile o Network profile o IO profile o Database profile
Introducing: Profiling...• Best thing would be to write bug free, high performant code• Normally development happens in iterative manner - get something to work and improve on that.• Basic profiling can help you to eliminate most of the memory and performance issues.
Right Tools...• There are many commercial and open source tools• We are going to use, o Jprofiler by ejTechnologies CPU, Memory, Allocation, Network, DB o Eclipse Memory Analyzer tool Find memory leaks o Standard JDK tooling - Jconsole Basic stats [image] http://writingsongs.com/pictures/toolbox.jpg
Setting up JProfiler• Profiling modes local/remote• Applying common filters for WSO2 products• Different views..
JProfiler Contd.CPU view - Call trees, Hot spotsMemory view - Allocation Hot spots, Recorded objects, Heap walkerVM telemetry view - Memory, Threads status graphsProbes - JDBC , Sockets
JConsole• Connect to the running instance local/remote• Different memory banks• Getting most out of Mbeans.• Getting a memory dump and analyzing with Eclipse MAT.• Remote JMX URL gets printed in the console during server startup: JMX Service URL : service:jmx:rmi://localhost:11111/jndi/rmi://localhost:9999/jmxrmi username : admin password : admin
Permgen Errors• Permgen space relates to the Programme code part, a.k.a - Loaded classes.• ClassLoader leaks• Typically happens in Container environments• Can uncover by doing deploy/redeploy cycles.• If one of the application objects get referenced by an object, outside the application, permgen error waiting to happen.
Memory Leaks - OOM• Languages like C, gave the control of memory to the programmer.• Java is a managed memory, language.• Still the JVM cant free up the memory, if the application is holding on to the objects.• Unnecessary accumulation of objects, o Object creation for each and every connection o Slow output rate in the input/output system o Collecting clusterwide messages without an upper bound.
DeadLocks Resource A Resource B• Re-designing the lock acquiring sequence• Using LockManagers that keeps track of lock acquisition
Liveness issues...• Starvation - A thread can starve for CPU cycles, if it is blocked by a lock-wait.• Poor Responsiveness• LiveLock scenarios
Programming Best Practices• Think about memory aspects/ data retrieval process while writing code.• Optimize the critical Path (look at CPU profile).• Make use of Standard libs as much as possible.• Profile your apps before releasing them to production.
Identity Server - Losing weight• Carbon server optimized to run in constrained memory environment.• No front end components - createWorker ant task.• Selective Admin service loading. -Doptimized=true• Removed unwanted functionality based on the use-case, (p2 - provisioning, etc)
Raspberry-Pi Clusters • Application server cluster running on R- Pis. • Powering the WSO2Con 2013 mobile app • 512MB of RAM and ARM processor.