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POWhy cannot the JVM auto expand heap memory to the configured Xmx3072m in linux & jdk1.6.0_32, and FullGC occurs very frequently
 

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  1. POWhy cannot the JVM auto expand heap memory to the configured Xmx3072m in linux & jdk1.6.0_32, and FullGC occurs very frequently
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    <p>Why the JVM memory cannot auto expand to Xmx3072m in linux &amp; jdk1.6.0_32?</p> <p>The Tenured generation is used 99% and lend the FullGC very frequence. The java process is using only 1G memory, as can be seen in the output of <code>top</code>.</p> <p>If we change the JVM parameters to <code>-Xms3072m -Xmx3072m</code>, then it works fine. But if we use <code>-Xms256m -Xmx3072m</code>, then the problem appears, and FullGC occurs very frequently. </p> <p>These 2 params are also default:</p> <pre><code>MinHeapFreeRatio 40 MaxHeapFreeRatio 70 </code></pre> <p>The environment is:</p> <pre><code>OS: Linux linux-wgvb 2.6.16.60-0.54.5-smp #1 SMP Fri Sep 4 01:28:03 UTC 2009 x86_64 x86_64 x86_64 GNU/Linux JDK version: java version "1.6.0_32" Java(TM) SE Runtime Environment (build 1.6.0_32-b05) Java HotSpot(TM) 64-Bit Server VM (build 20.7-b02, mixed mode) JVM params: -Xms256m -Xmx3072m -XX:+UseParallelOldGC -XX:MaxGCPauseMillis=1000 -XX:ParallelGCThreads=5 -Xrs -XX:PermSize=64m -XX:MaxPermSize=512m -XX:+HeapDumpOnOutOfMemoryError </code></pre> <p>FullGC is executed frequently:</p> <pre><code>@linux&gt; ./jstat -gcutil 18261 1000 500 S0 S1 E O P YGC YGCT FGC FGCT GCT 0.00 64.67 7.04 99.53 71.89 18293 510.574 1167 1616.594 2127.168 91.78 7.91 100.00 99.53 72.00 18299 510.821 1167 1616.594 2127.415 77.49 0.00 0.00 99.99 72.00 18300 510.947 1168 1616.594 2127.541 0.00 99.83 25.71 99.49 71.72 18305 511.178 1168 1617.915 2129.093 24.27 0.00 21.74 99.67 71.73 18310 511.342 1168 1617.915 2129.256 28.57 0.00 0.00 99.83 71.73 18314 511.427 1169 1617.915 2129.342 0.00 29.29 0.00 99.56 71.82 18317 511.465 1169 1618.919 2130.384 0.00 78.85 54.96 99.56 72.05 18326 511.777 1169 1618.919 2130.696 64.52 0.00 0.00 99.99 72.05 18328 511.920 1170 1618.919 2130.839 0.00 99.26 0.00 99.88 71.71 18333 512.079 1171 1620.014 2132.093 4.86 0.00 0.00 99.95 71.76 18338 512.255 1172 1620.957 2133.211 80.98 0.00 0.00 99.69 71.83 18350 512.453 1172 1621.906 2134.359 0.00 64.48 0.00 99.85 71.83 18355 512.677 1173 1621.906 2134.583 0.00 99.80 0.00 99.93 71.71 18359 512.876 1174 1623.264 2136.139 0.06 0.04 100.00 99.55 71.71 18360 512.876 1174 1624.193 2137.069 60.35 0.00 0.00 99.90 71.77 18376 513.429 1175 1624.193 2137.622 60.35 0.00 0.00 99.90 71.77 18376 513.429 1175 1624.193 2137.622 89.86 0.00 0.00 99.83 71.78 18384 513.839 1176 1625.476 2139.315 89.86 0.00 0.00 99.83 71.78 18384 513.839 1176 1625.476 2139.315 0.00 39.17 64.41 99.60 71.78 18394 514.202 1176 1626.880 2141.082 99.93 0.00 0.00 99.82 71.78 18396 514.326 1177 1626.880 2141.206 0.00 64.68 0.00 99.61 71.72 18401 514.409 1177 1627.945 2142.354 </code></pre> <p>The java process only used 1G memory:</p> <pre><code> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 18261 ouser 15 0 4353m 1.0g 52m S 325 3.2 271:25.52 java </code></pre> <pre> ./jstat -gccapacity 18261 1000 500 NGCMN NGCMX NGC S0C S1C EC OGCMN OGCMX OGC OC PGCMN PGCMX PGC PC YGC FGC 87360.0 1048576.0 136256.0 65984.0 68096.0 64.0 174784.0 2097152.0 785664.0 785664.0 65536.0 524288.0 65792.0 65792.0 141612 8100 87360.0 1048576.0 122816.0 61376.0 12992.0 64.0 174784.0 2097152.0 791360.0 791360.0 65536.0 524288.0 65792.0 65792.0 141616 8100 87360.0 1048576.0 115264.0 57600.0 7872.0 64.0 174784.0 2097152.0 791936.0 791936.0 65536.0 524288.0 65792.0 65792.0 141617 8101 87360.0 1048576.0 112576.0 54912.0 56256.0 64.0 174784.0 2097152.0 797952.0 797952.0 65536.0 524288.0 65792.0 65792.0 141618 8102 87360.0 1048576.0 112576.0 54912.0 56256.0 64.0 174784.0 2097152.0 797952.0 797952.0 65536.0 524288.0 65792.0 65792.0 141618 8102 87360.0 1048576.0 105408.0 52672.0 192.0 64.0 174784.0 2097152.0 804096.0 804096.0 65536.0 524288.0 65792.0 65792.0 141621 8103 87360.0 1048576.0 87360.0 35584.0 38464.0 8064.0 174784.0 2097152.0 805568.0 805568.0 65536.0 524288.0 65792.0 65792.0 141629 8103 87360.0 1048576.0 111168.0 39488.0 46080.0 12416.0 174784.0 2097152.0 805568.0 805568.0 65536.0 524288.0 65792.0 65792.0 141635 8103 87360.0 1048576.0 142848.0 69440.0 70592.0 1664.0 174784.0 2097152.0 805568.0 805568.0 65536.0 524288.0 65792.0 65792.0 141644 8104 87360.0 1048576.0 142848.0 69440.0 70592.0 1664.0 174784.0 2097152.0 805568.0 805568.0 65536.0 524288.0 65792.0 65792.0 141644 8104 87360.0 1048576.0 87360.0 35136.0 37376.0 10304.0 174784.0 2097152.0 769280.0 769280.0 65536.0 524288.0 65792.0 65792.0 141661 8105 </pre>
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    1. COI do not understand why people downvote this, its a perfectly valid GC-issue question providing enough evidence about the problem.
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