# ct-study-jvm-benchmark-test

**Repository Path**: cachetian/ct-study-jvm-benchmark-test

## Basic Information

- **Project Name**: ct-study-jvm-benchmark-test
- **Description**: JVM heap memory benchmark test
- **Primary Language**: Unknown
- **License**: MIT
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2020-12-30
- **Last Updated**: 2021-01-09

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# java-jvm-benchmark-test

## test case 01 - hello-world

-XX:PermSize=size changed to -XX:MetaspaceSize=size
```shell script
java -Xmx4096m -XX:MaxPermSize=1024m HelloWorldMain
java -Xmx4096m -XX:MetaspaceSize=1024m HelloWorldMain
java -Xms4096m -Xmx4096m -XX:MetaspaceSize=1024m -XX:MetaspaceSize=1024m HelloWorldMain
```
#### referenced links:
https://stackoverflow.com/questions/5891123/specifying-jvm-arguments-when-calling-a-jar-file
https://stackoverflow.com/questions/12114174/what-does-xxmaxpermsize-do
https://www.oracle.com/java/technologies/javase/gc-tuning-6.html
https://stackoverflow.com/questions/22634644/java-hotspottm-64-bit-server-vm-warning-ignoring-option-maxpermsize
https://help.sap.com/doc/saphelp_nw75/7.5.5/en-US/f0/cec51dabd1461b87e4db9e3958710e/loio44a438452ba94658a8e21f998d248fa4_HiRes.png
![JVM](https://help.sap.com/doc/saphelp_nw75/7.5.5/en-US/f0/cec51dabd1461b87e4db9e3958710e/loio44a438452ba94658a8e21f998d248fa4_HiRes.png)
https://www.cnblogs.com/SIHAIloveYAN/p/12023615.html
> -Xms
初始堆的大小，也是堆大小的最小值，默认值是总共的物理内存/64（且小于1G）。默认情况下，当堆中可用内存小于40%，堆内存会开始增加，一直增加到-Xmx的大小。

https://stackoverflow.com/questions/31455644/should-i-set-a-maxmetaspacesize/31463972#31463972
> As I commented on the previous answer the reasons for setting a limit on those memory pools is different.
If your users previously increased the MaxPermSize above the default that probably was either to avoid Full GCs / concurrent mode failures with CMS or because their applications genuinely needed a lot of perm gen space.
Decreasing the the metaspace limit from its effectively infinite default would serve an entirely different purpose: Avoiding unbounded metaspace growth.
The thing is that that's just an upper limit. The actually committed, i.e. current metaspace size will be smaller. In fact, there is a setting called MaxMetaspaceFreeRatio (default 70%) which means that the actual metaspace size will never exceed 230% of its occupancy.
And for it to grow it first would have to fill up, forcing a garbage collection (metaspace full) in an attempt to free objects and only when it cannot meet its MinMetaspaceFreeRatio (default 40%) goal it would expand the current metaspace to no more than 230% of the occupancy after the GC cycle.
So in practice the actual metaspace size should stabilize within a band close relative to its actual need unless the application is continuously leaking classloaders/classes or generating an enormous amount of dynamic code.
TL;DR: There may be reasons to restrict metaspace size, but they likely are different to the original reasons for setting the perm gen sizes. Therefore the need should be re-evaluated.
```
#### 介绍
JVM heap memory benchmark test

#### 软件架构
软件架构说明


#### 安装教程

1.  xxxx
2.  xxxx
3.  xxxx

#### 使用说明

1.  xxxx
2.  xxxx
3.  xxxx

#### 参与贡献

1.  Fork 本仓库
2.  新建 Feat_xxx 分支
3.  提交代码
4.  新建 Pull Request


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