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    JP 7 2 Practice Solution

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    Nur Aini Ardian
    This document discusses Java memory structure and garbage collection. It introduces the Java heap memory and defines key terms like heap, minor GC, metaspace, and full GC. It provides exercises to analyze Java Virtual Machine (JVM) garbage collection (GC) activities like checking GC logs and using jstat to monitor heap usage with different application memory sizes. The exercises demonstrate how memory is allocated in the young and old generations and tenured space of the JVM heap.

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    JP 7 2 Practice Solution

    Uploaded by

    Nur Aini Ardian
    22 views4 pages
    This document discusses Java memory structure and garbage collection. It introduces the Java heap memory and defines key terms like heap, minor GC, metaspace, and full GC. It provides exercises to analyze Java Virtual Machine (JVM) garbage collection (GC) activities like checking GC logs and using jstat to monitor heap usage with different application memory sizes. The exercises demonstrate how memory is allocated in the young and old generations and tenured space of the JVM heap.

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    This document discusses Java memory structure and garbage collection. It introduces the Java heap memory and defines key terms like heap, minor GC, metaspace, and full GC. It provides exercises to analyze Java Virtual Machine (JVM) garbage collection (GC) activities like checking GC logs and using jstat to monitor heap usage with different application memory sizes. The exercises demonstrate how memory is allocated in the young and old generations and tenured space of the JVM heap.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    22 views4 pages

    JP 7 2 Practice Solution

    Uploaded by

    Nur Aini Ardian
    This document discusses Java memory structure and garbage collection. It introduces the Java heap memory and defines key terms like heap, minor GC, metaspace, and full GC. It provides exercises to analyze Java Virtual Machine (JVM) garbage collection (GC) activities like checking GC logs and using jstat to monitor heap usage with different application memory sizes. The exercises demonstrate how memory is allocated in the young and old generations and tenured space of the JVM heap.

    Copyright:

    © All Rights Reserved
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    Download as pdf or txt
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    Java Programming

    7-2: Java Memory Structure


    Practice Solutions

    Lesson Objectives:
    • Introduce Java Heap Memory
    • Garbage collection
    • Analyze the Memory allocation in JVM

    Vocabulary:

    Identify the vocabulary word for each definition below.

    Heap A data area from which memory for all class instances and arrays is allocated

    Minor GC The GC which collects garbage from the Young space (Eden and Survivor spaces)

    Metaspace The memory area that contains the class metadata.

    Full GC The GC that collects garbage from the Tenured space.

    Copyright © 2020, Oracle and/or its affiliates. All rights reserved. Oracle and Java are registered trademarks of Oracle and/or its affiliates. Other names may be trademarks of their respective owners.
    Try It/Solve It:
    Run the Testing Program
    java -verbose:gc -Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8 -
    XX:+PrintCommandLineFlags -XX:+PrintTenuringDistribution -jar TestMemory.jar

    Give different size of Memory to check the activities of JVM GC.

    1. Check the output from the console of the Java command. How Many GC happened during the startup of
    the program?

    2. Use jps to list the active Java process.

    C:\tmp>jps -l
    2088 sun.tools.jps.Jps
    21000 TestMemory.jar

    3. Use the jstat command to check the output and find the change of heap.

    Copyright © 2020, Oracle and/or its affiliates. All rights reserved. Oracle and Java are registered trademarks of Oracle and/or its affiliates. Other names may be trademarks of their respective owners.

    2
    4. Give the value of 1M input to the application.

    - Analyze the following output: from the java console

    [GC (Allocation Failure)


    Desired survivor size 1048576 bytes, new threshold 7 (max 15)
    [PSYoungGen: 8849K->1016K(9216K)] 11741K->9410K(19456K), 0.0281064 secs] [Times:user=0.03
    sys=0.00, re-al=0.03 secs]
    [Full GC (Ergonomics) [PSYoungGen: 1016K->0K(9216K)] [ParOldGen: 8394K->7305K(10240K)] 9410K-
    >7305K(19456K), [Metaspace: 14327K->14327K(1062912K)], 0.0395641 secs]
    Times: user=0.03 sys=0.00, real=0.04 secs]

    - Analyze the data from the output of jstat

    5. Print out the time of the GC happened.

    Use -XX:+PrintGCTimeStamps

    Copyright © 2020, Oracle and/or its affiliates. All rights reserved. Oracle and Java are registered trademarks of Oracle and/or its affiliates. Other names may be trademarks of their respective owners.

    3
    6. Run the application sizetest.jar:
    java -verbose:gc -Xms20M -Xmx20M -Xmn10M -XX:+PrintGCDetails -XX:SurvivorRatio=8 -
    XX:+PrintTenuringDistribution -XX:PretenureSizeThreshold=20000 -jar sizetest.jar

    In this lab, the program will generate 4 MB heap memory, but the data will reside in the Tenured area, not in
    the Young Eden space.

    7. Check the output from the jstat utility. Where is the 4 MB heap memory located?

    Notice the size of OU from 2901.9 – 7717.9

    Copyright © 2020, Oracle and/or its affiliates. All rights reserved. Oracle and Java are registered trademarks of Oracle and/or its affiliates. Other names may be trademarks of their respective owners.

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