J2se 1 5 memory heap and garbage collector
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J2SE 1.5 : Memory Heap and Garbage Collector. Objectives. You will be able to understand the JVM Memory Heap You will be able to know what the Garbage Collector do You will be able to understand the impact of GC on J2EE application performance. JVM Object Garbage Collection.

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J2SE 1.5 : Memory Heap and Garbage Collector

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J2SE 1.5 : Memory Heap and Garbage Collector


Objectives

  • You will be able to understand the JVM Memory Heap

  • You will be able to know what the Garbage Collector do

  • You will be able to understand the impact of GC on J2EE application performance


JVM Object Garbage Collection

  • GC shields the developer from the complexity of memory allocation and garbage collection

  • GC is one of the principal bottleneck of J2EE applications

  • OutOfMemoryExceptions

  • Memory Leak


Generations


Generations


Generations

If the garbage collector has become a bottleneck, you may wish to customize the generation sizes. Check the verbose garbage collector output, and then explore the sensitivity of your individual performance metric to the garbage collector parameters.


Garbage Collection Schemes


Throughput Collector

  • The Throughput Collector is selected by the default if the JVM is runinng in server mode

  • Can be enabled using the command line flag -XX:+UseParallelGC


Throughput Collector


Performance Consideration

  • Throughput: percentage of total time not spent in garbage collection

  • Pauses: the times when an application appears unresponsive because garbage collection is occurring


Measurement: Command Line

  • -verbose:gc

  • -XX:PrintGCDetails

  • -XX:PrintGCTimeStamp

  • -XX:+PrintTenuringDistribution

  • -XX:PrintHeapAtGC

  • -Xloggc:<filename>


Measurement : -verbose:gc


Measurement: -XX:PrintGCDetails


Measurement: PrintHeapAtGC


Measurement: visualgc


Measurement: JConsole


Sizing Generations


Sizing the Generations

  • -Xms<size>

  • -Xmx<size>

  • -XX:NewSize=<size>

  • -XX:MaxNewSize=<size>

  • -XX:MaxPermSize=<size>

  • -XX:+UseTLAB

  • -XX:MaxTenuredThreshhold=32


Sizing the Generations

JAVA_OPTS=$JAVA_OPTS

-Xms1200m –Xmx1200m

–XX:NewSize=400M

–XX:MaxNewSize=400M

–XX:SurvivorRatio=32

–XX:+UseTLAB –XX:TLABSize=64K


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