添加go对map的使用注意

README.md

@@ -1,74 +1,73 @@
-# groupcache
-
-## Summary
-
-groupcache is a distributed caching and cache-filling library, intended as a
-replacement for a pool of memcached nodes in many cases.
-
-For API docs and examples, see http:https://godoc.org/github.com/golang/groupcache
-
-## Comparison to memcached
-
-### **Like memcached**, groupcache:
-
- * shards by key to select which peer is responsible for that key
-
-### **Unlike memcached**, groupcache:
-
- * does not require running a separate set of servers, thus massively
- reducing deployment/configuration pain. groupcache is a client
- library as well as a server. It connects to its own peers, forming
- a distributed cache.
-
- * comes with a cache filling mechanism. Whereas memcached just says
- "Sorry, cache miss", often resulting in a thundering herd of
- database (or whatever) loads from an unbounded number of clients
- (which has resulted in several fun outages), groupcache coordinates
- cache fills such that only one load in one process of an entire
- replicated set of processes populates the cache, then multiplexes
- the loaded value to all callers.
-
- * does not support versioned values. If key "foo" is value "bar",
- key "foo" must always be "bar". There are neither cache expiration
- times, nor explicit cache evictions. Thus there is also no CAS,
- nor Increment/Decrement. This also means that groupcache....
-
- * ... supports automatic mirroring of super-hot items to multiple
- processes. This prevents memcached hot spotting where a machine's
- CPU and/or NIC are overloaded by very popular keys/values.
-
- * is currently only available for Go. It's very unlikely that I
- (bradfitz@) will port the code to any other language.
-
-## Loading process
-
-In a nutshell, a groupcache lookup of **Get("foo")** looks like:
-
-(On machine #5 of a set of N machines running the same code)
-
- 1. Is the value of "foo" in local memory because it's super hot? If so, use it.
-
- 2. Is the value of "foo" in local memory because peer #5 (the current
- peer) is the owner of it? If so, use it.
-
- 3. Amongst all the peers in my set of N, am I the owner of the key
- "foo"? (e.g. does it consistent hash to 5?) If so, load it. If
- other callers come in, via the same process or via RPC requests
- from peers, they block waiting for the load to finish and get the
- same answer. If not, RPC to the peer that's the owner and get
- the answer. If the RPC fails, just load it locally (still with
- local dup suppression).
-
-## Users
-
-groupcache is in production use by dl.google.com (its original user),
-parts of Blogger, parts of Google Code, parts of Google Fiber, parts
-of Google production monitoring systems, etc.
-
-## Presentations
-
-See http:https://talks.golang.org/2013/oscon-dl.slide
-
-## Help
-
-Use the golang-nuts mailing list for any discussion or questions.
+## groupcache快速入门
+
+### 功能介绍
+groupcache是go语言开发的缓存库。用于替换memcache的。
+#### 客户端行为
+```text
+当客户端连上groupcache时，能做的只有get获取数据，如果本地有所需要的数据，则直接返回，
+如果没有，则通过一致性哈希函数判断这个key所对应的peer，然后通过http从这个peer上获取数据；
+如果这个peer上有需要的数据，则通过http回复给之前的那个groupcache；groupcache收到之后，保存在本地hotCache中，并返回给客户端；
+如果peer上也没有所需要的数据，则groupcache从数据源(数据库或者文件)获取数据，并将数据保存在本地mainCache，并返回给客户端
+```
+
+#### 系统框架
+![](./2.png)
+
+
+#### 代码框架
+![](./1.png)
+
+
+#### 制约
++ 只能get、remove，不支持update，只能remove后再get
++ 过期机制为限制cache队列长度，不能设置过期时间，只能通过内置lru淘汰过期数据；
++ 经常变更的数据不适合groupcache作为缓存；
+注意一点，groupcache的consistenhash实现只能增加节点，无法减少节点，若要实现该功能，要注意当减少节点时，
+如果有相同的虚拟节点映射到同一个位置，则要判断删除的数量。增加不存在问题，因为增加的时候后来的虚拟节点可以替换先设置的虚拟节点，不影响使用。
+
+### 使用入门
+```shell
+cd example
+go build
+./example -addr=:8080 -pool=http:https://127.0.0.1:8080 
+
+# 查询
+curl localhost:8080/color?name=green
+#00FF00
+curl localhost:8080/color?name=red
+#FF0000
+
+```
+
+### 源码目录
+ ```shell script
+.
+├── byteview.go // 封装了字节切片的多种操作方法
+├── consistenthash // 提供了分布式一致性hash的抽象，其本身并没有实现分布式一致性的hash，而是可以以指定的hash完成分布式一致性的key的定位和节点的增加，注意这里没有实现节点删除。
+├── groupcache.go // grpc生成的代码，用于远程调用
+├── groupcachepb // 提供了上述节点之间其消息序列化和反序列化协议，基于protobuf，在groupcache.proto中定义。
+├── http.go // 实现了peers之间的http查询缓存的请求方法和响应服务
+├── lru // 实现缓存的置换算法（最近最少使用）
+├── peers.go // 抽象了缓存节点，提供了注册、获取节点的机制
+├── singleflight // 实现多个同请求的合并，保证“同时”多个同参数的get请求只执行一次操作功能
+├── sinks.go // 抽象了数据容器, 可以以不同的方法初始化设置，最终以统一的字节切片读出
+└── testpb
+
+```
+
+### 分析目的
++ consistenthash(提供一致性哈希算法的支持)，
++ lru(提供了LRU方式清楚缓存的算法)，
++ singleflight(保证了多次相同请求只去获取值一次，减少了资源消耗)，
+
+### 问题
++ 节点销毁怎么处理？
++ 数据更新或者删除？
+ https://github.com/mailgun/groupcache
+
+
+### 参考资料
++ [《groupcache 设计原理剖析 》](https://www.dazhuanlan.com/2019/12/11/5df07fcb62cae/?__cf_chl_jschl_tk__=e5a47b230d1b9d89eb3887cab036b09f2e3ea621-1590370196-0-AYcPFk14NmbUvag0bCwvLEwPGpXssbJuZhDvEpan7iZiKQi123FXqUvH-LsRSQaov7ybpQtzh-615A-1ZEDC54TuWv_6ZTwsr3zoEwubtJbUbw2J8PTOnzfviGoQB4UWA9Y1ZVzP5QLQ2BCSNlSYxDlegJsosJAV1xJQf06FNkbXPBEAh0SCE29OAzUhpZx1qOKfiUjkI1NNltnexAUoGKVMymm9ocKiWwcq4y_CnUX3xNGz6wyOTmUjQ0RrS1qcQDN8Z-0Jrzn9z1VbzCbEc8R-bdwdkzo7hqaHZ3goA0AQMpxVWxzRjbsy4YIf7vHWEg)
++ [《GROUPCACHE EXAMPLE》](https://sconedocs.github.io/groupcacheUseCase/)
++ [Playing with groupcache](https://capotej.com/blog/2013/07/28/playing-with-groupcache/)
++ [《从入门到掉坑：Go 内存池/对象池技术介绍》](https://cloud.tencent.com/developer/article/1638446)