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runbroker.sh
#===========================================================================================
# JVM Configuration
#===========================================================================================
JAVA_OPT="${JAVA_OPT} -server -Xms4g -Xmx4g -Xmn2g -XX:PermSize=128m -XX:MaxPermSize=320m"
JAVA_OPT="${JAVA_OPT} -XX:+UseConcMarkSweepGC -XX:+UseCMSCompactAtFullCollection -XX:CMSInitiatingOccupancyFraction=70 -XX:+CMSParallelRemarkEnabled -XX:SoftRefLRUPolicyMSPerMB=0 -XX:+CMSClassUnloadingEnabled -XX:SurvivorRatio=8 -XX:+DisableExplicitGC"
JAVA_OPT="${JAVA_OPT} -verbose:gc -Xloggc:${HOME}/rmq_bk_gc.log -XX:+PrintGCDetails -XX:+PrintGCDateStamps"
JAVA_OPT="${JAVA_OPT} -XX:-OmitStackTraceInFastThrow"
JAVA_OPT="${JAVA_OPT} -Djava.ext.dirs=${BASE_DIR}/lib"
#JAVA_OPT="${JAVA_OPT} -Xdebug -Xrunjdwp:transport=dt_socket,address=9555,server=y,suspend=n"
JAVA_OPT="${JAVA_OPT} -cp ${CLASSPATH}"
-server By default, all client applications run in -client mode, while the directory server and certain server utilities run in -server mode. Generally, -server mode provides higher throughput than -client mode, at the expense of slightly longer startup times.
-Xms4g Sets the initial size (in bytes) of the heap. This value must be a multiple of 1024 and greater than 1 MB. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes.
-Xmx4g Specifies the maximum size (in bytes) of the memory allocation pool in bytes.This value must be a multiple of 1024 and greater than 2 MB. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The default value is chosen at runtime based on system configuration. For server deployments, -Xms and -Xmx are often set to the same value. See the section "Ergonomics" in Java SE HotSpot Virtual Machine Garbage Collection Tuning Guide.
click to see configuring-the-default-jvm-and-java-arguments
-Xmn2g Sets the initial and maximum size (in bytes) of the heap for the young generation (nursery). Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes.
The young generation region of the heap is used for new objects. GC is performed in this region more often than in other regions. If the size for the young generation is too small, then a lot of minor garbage collections will be performed. If the size is too large, then only full garbage collections will be performed, which can take a long time to complete. Oracle recommends that you keep the size for the young generation between a half and a quarter of the overall heap size. 7 8
-XX:PermSize=128m Sets the space (in bytes) allocated to the permanent generation that triggers a garbage collection if it is exceeded. This option was deprecated un JDK 8, and superseded by the -XX:MetaspaceSize option.
-XX:MaxPermSize=320m Sets the maximum permanent generation space size (in bytes). This option was deprecated in JDK 8, and superseded by the -XX:MaxMetaspaceSize option.
-XX:+UseConcMarkSweepGC Enables the use of the CMS garbage collector for the old generation. Oracle recommends that you use the CMS garbage collector when application latency requirements cannot be met by the throughput (-XX:+UseParallelGC) garbage collector. The G1 garbage collector (-XX:+UseG1GC) is another alternative. By default, this option is disabled and the collector is chosen automatically based on the configuration of the machine and type of the JVM. When this option is enabled, the -XX:+UseParNewGC option is automatically set and you should not disable it, because the following combination of options has been deprecated in JDK 8: -XX:+UseConcMarkSweepGC -XX:-UseParNewGC.
-XX:+UseParNewGC Enables the use of parallel threads for collection in the young generation. By default, this option is disabled. It is automatically enabled when you set the -XX:+UseConcMarkSweepGC option. Using the -XX:+UseParNewGC option without the -XX:+UseConcMarkSweepGC option was deprecated in JDK 8.
-XX:+UseCMSCompactAtFullCollection 表示在FGC之后进行压缩，因为CMS默认不压缩空间的。
-XX:CMSInitiatingOccupancyFraction=70 使用cms作为垃圾回收，使用70％后开始CMS收集。
-XX:+CMSParallelRemarkEnabled 开启并行标记。
-XX:SoftRefLRUPolicyMSPerMB=0 每兆堆空闲空间中SoftReference的存活时间。This flag enables aggressive processing of software references. Use this flag if the software reference count has an impact on the Java HotSpot VM garbage collector.
-XX:+CMSClassUnloadingEnabled Enables class unloading when using the concurrent mark-sweep (CMS) garbage collector. This option is enabled by default. To disable class unloading for the CMS garbage collector, specify -XX:-CMSClassUnloadingEnabled.
-XX:SurvivorRatio=8 Sets the ratio between eden space size and survivor space size. By default, this option is set to 8. The following example shows how to set the eden/survivor space ratio to 4:-XX:SurvivorRatio=4
-XX:+DisableExplicitGC 关闭System.gc()
-verbose:gc Displays information about each garbage collection (GC) event.
-Xloggc:${HOME}/rmq_bk_gc.log Sets the file to which verbose GC events information should be redirected for logging. The information written to this file is similar to the output of -verbose:gc with the time elapsed since the first GC event preceding each logged event. The -Xloggc option overrides -verbose:gc if both are given with the same java command.
-XX:+PrintGCDetails Enables printing of detailed messages at every GC. By default, this option is disabled.
-XX:+PrintGCDateStamps Enables printing of a date stamp at every GC. By default, this option is disabled.
RocketMQ runbroker.sh 分析JVM启动参数
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原文地址：http://www.cnblogs.com/zno2/p/4599345.html
