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pull merged 2 commits into from
Sep 15, 2021
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[pull] master from Snailclimb:master #204

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Update ConcurrentHashMap源码+底层数据结构分析.md
Snailclimb Sep 15, 2021
e4a4e1c
Update 最重要的JVM参数指南.md
Snailclimb Sep 15, 2021
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4 changes: 3 additions & 1 deletion docs/java/collection/ConcurrentHashMap源码+底层数据结构分析.md
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### 1. 存储结构

> 下图存在一个笔误 Segmeng -> Segment

![Java 7 ConcurrentHashMap 存储结构](./images/image-20200405151029416.png)

Java 7 中 ConcurrentHashMap 的存储结构如上图，ConcurrnetHashMap 由很多个 Segment 组合，而每一个 Segment 是一个类似于 HashMap 的结构，所以每一个 HashMap 的内部可以进行扩容。但是 Segment 的个数一旦**初始化就不能改变**，默认 Segment 的个数是 16 个，你也可以认为 ConcurrentHashMap 默认支持最多 16 个线程并发。
Java 7 中 `ConcurrentHashMap` 的存储结构如上图，`ConcurrnetHashMap` 由很多个 `Segment` 组合，而每一个 `Segment` 是一个类似于 HashMap 的结构，所以每一个 `HashMap` 的内部可以进行扩容。但是 `Segment` 的个数一旦**初始化就不能改变**，默认 `Segment` 的个数是 16 个，你也可以认为 `ConcurrentHashMap` 默认支持最多 16 个线程并发。

### 2. 初始化

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2 changes: 1 addition & 1 deletion docs/java/jvm/最重要的JVM参数指南.md
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-Xms2G -Xmx5G
```

### 2.2.显式新生代内存(Young Ceneration)
### 2.2.显式新生代内存(Young Generation)

根据[Oracle官方文档](https://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/sizing.html)，在堆总可用内存配置完成之后，第二大影响因素是为 `Young Generation` 在堆内存所占的比例。默认情况下，YG 的最小大小为 1310 *MB*，最大大小为*无限制*。

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