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

J2SE 1.5 : Memory Heap and Garbage Collector


Objectives

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

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


Generations1

Generations


Generations2

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

Garbage Collection Schemes


Throughput collector

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 collector1

Throughput Collector


Performance consideration

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

Measurement: Command Line

  • -verbose:gc

  • -XX:PrintGCDetails

  • -XX:PrintGCTimeStamp

  • -XX:+PrintTenuringDistribution

  • -XX:PrintHeapAtGC

  • -Xloggc:<filename>


Measurement verbose gc

Measurement : -verbose:gc


Measurement xx printgcdetails

Measurement: -XX:PrintGCDetails


Measurement printheapatgc

Measurement: PrintHeapAtGC


Measurement visualgc

Measurement: visualgc


Measurement jconsole

Measurement: JConsole


Sizing generations

Sizing Generations


Sizing the generations

Sizing the Generations

  • -Xms<size>

  • -Xmx<size>

  • -XX:NewSize=<size>

  • -XX:MaxNewSize=<size>

  • -XX:MaxPermSize=<size>

  • -XX:+UseTLAB

  • -XX:MaxTenuredThreshhold=32


Sizing the generations1

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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