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Java Performance -War Stories

Paul McLachlanApptio

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Performance Strategy

Performance tuning is a discipline

– Measure, Don’t (ever) guess– Always attack #1 bottleneck first– Is success possible?

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Performance Strategies

– Call it less– Make it more efficient– Do it in parallel

– Do it beforehand

or…

Performance Strategy

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“Perceived Performance”

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Example

Performance Tuning By Example

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A random bottleneck

This is an example – please ignore the SQL stupidity

(Actually – all of these snippets are for explanation purposes, YAMMV)

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Add a cache

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Don’t synchronize on the DB

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Use ConcurrentHashMap

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Don’t thrash with simultaneous hits

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Don’t run out of RAM

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Soft References

Weak/Soft/Phantom/Final References

http://jeremymanson.blogspot.com/2009/07/how-hotspot-decides-to-clear_07.html

-XX:SoftRefLRUPolicyMSPerMB=1

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Preload everything beforehand

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Use less RAM with .intern()

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How to make HashMap.get() faster?

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HotCache pattern

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Example

Memory Optimizations

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How Much Memory?

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How Much Memory?

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How Much Memory?org.apache.commons.collections.map.Flat3Map

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*How* Much Memory?

-XX:+UseCompressedOops

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Off Heap

Off Heap &Native Integration Tricks

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“Unsafe”

http://javasourcecode.org/html/open-source/jdk/jdk-6u23/sun/misc/Unsafe.java.html

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Off Heap / Mapped Wrapping Classes

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Example

Build In Instrumentation

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Visibility

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Memory Report

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Visibility

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Visibility

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/OutputThreads Servlet

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Example

Or … Tools

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Tools / YourKit

yourkit.com:

Sampling Instrumenting Heap & GC

$500 / unlimited

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How Profilers Work

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Or … Embed the Profiler

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Tools / NMon http://nmon.sourceforge.net

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Example

Reference Material

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Numbers Everyone Should Knowhttp://www.cs.cornell.edu/projects/ladis2009/talks/dean-keynote-ladis2009.pdf

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Statistics Relative Standard Deviation =

STDEV(…)/AVERAGE(…) Confidence = 1-TTEST(orig,control,1,2)

Throughput Average latency Max latency 90th Percentile latency

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Tools

jHiccuphttp://www.azulsystems.com/jHiccup

YourKithttp://yourkit.com/

Nmon for Linuxhttp://nmon.sourceforge.net

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Libraries

CLHM http://code.google.com/p/concurrentlinkedhashmap/

Guavahttp://code.google.com/p/guava-libraries/

Colthttp://acs.lbl.gov/software/colt/

Trove4Jhttp://trove.starlight-systems.com/

JDK 8 Concurrency Codehttp://gee.cs.oswego.edu/dl/concurrency-interest/index.html

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Good Books / References

Java Memory Modelhttp://www.cs.umd.edu/~pugh/java/memoryModel/

Java Platform Performancehttp://java.sun.com/docs/books/performance/

Debugging by Thinkinghttp://www.debuggingbythinking.com/

Concurrent Programming in Javahttp://www.amazon.com/Concurrent-Programming-Java-Principles-Pattern/dp/0201310090/

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JVM Intrinsicshttp://hg.openjdk.java.net/jdk6/jdk6/hotspot/file/6d13fcb3663f/ src/share/vm/classfile/vmSymbols.hpp