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https://issues.apache.org/jira/browse/ROCKETMQ-307?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16236925#comment-16236925
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ASF GitHub Bot commented on ROCKETMQ-307:
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johnsonyang commented on issue #186: [ROCKETMQ-307] Polish the JVM parameters
in start scriptes
URL: https://github.com/apache/rocketmq/pull/186#issuecomment-341602398
Hi, zhou
thanks you feedback quickly!
1. From the jvm arguments view, the `MetaspaceSize` and `MaxMetaspaceSize`
in JDK8 used to replace the `-XX:PermSize` and `-XX:MaxPermSize`, in JDK8,
Metaspace（JEP 122）used to replace the PermGen space to improve GC performance.
The Metaspace used the direct memory, as I know, the default value is no limit
if NOT set a value, it will use all memory.
2. The `MetaspaceSize` and `MaxMetaspaceSize` be introduced from JDK8, I
also check the rocketMQ [releases
note](https://rocketmq.apache.org/dowloading/releases/), the rocket recommend
used the JDK8 on the Broker and NameServer, below info for your check quickly!
|Version| Client| Broker| NameServer|
|4.0.0-incubating| >=1.7| >=1.8| >=1.8|
|4.1.0-incubating| >=1.6| >=1.8| >=1.8|
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> some jvm arguments need changed for java 8 and direct memory GC
> ---------------------------------------------------------------
>
> Key: ROCKETMQ-307
> URL: https://issues.apache.org/jira/browse/ROCKETMQ-307
> Project: Apache RocketMQ
> Issue Type: Improvement
> Components: rocketmq-externals
> Affects Versions: 4.2.0
> Environment: all
> Reporter: johnsonyjl
> Assignee: dongeforever
> Priority: Major
> Fix For: 4.2.0
>
>
> * new jvm arguments -XX:MetaspaceSize=128m -XX:MaxMetaspaceSize=320m for jdk 8
> * remove the -XX:+DisableExplicitGC, if use the DisableExplicitGC, the direct
> memory GC will be not run correctly. please refer to
> java.nio.Bits#reserveMemory method
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