# 缓存

缓存用于减轻后端服务压力。缓存可以分为 服务端缓存(redis，ehcache)、客户端缓存(localstorage)、代理缓存(nginx)。nginx的缓存服务就是代理缓存。

![1556159422900](/files/pvrNKZiIRLSg2wv2tPy5)

## proxy\_cache

proxy\_cache的配置同样位于proxy代理模块，相关配置比较多，一下是较为常用的几个配置：

```nginx
# 配置缓存文件 path路径
Syntax:	proxy_cache_path path [levels=levels] [use_temp_path=on|off] keys_zone=name:size [inactive=time] [max_size=size] [manager_files=number] [manager_sleep=time] [manager_threshold=time] [loader_files=number] [loader_sleep=time] [loader_threshold=time] [purger=on|off] [purger_files=number] [purger_sleep=time] [purger_threshold=time];
Default:	—
Context:	http

# 开启代理缓存，zone代表哪个path
Syntax:	proxy_cache zone | off;
Default:	proxy_cache off;
Context:	http, server, location

# 缓存有效期配置
Syntax:	proxy_cache_valid [code ...] time;
Default:	—
Context:	http, server, location

# 缓存维度配置，即配置key
Syntax:	proxy_cache_key string;
Default:	proxy_cache_key $scheme$proxy_host$request_uri;
Context:	http, server, location
```

## 示例配置

```nginx
upstream blog {    
    server 192.168.0.159:8080;
    server 192.168.0.159:8081; 
    server 192.168.0.159:8082; 
}

# /opt/app/cache 缓存存储路径
# levels 按照目录进行归并和分级，1:2 代表两层目录进行分级
# keys_zone 定义开辟zone空间的名称，以供下面引用，10m代表大小，1m大约可以存放8000个key
# max_size 缓存目录最大多大，用满之后就会触发淘汰规则 
# inactive=60m 超过60分钟的未被访问的缓存空间，此缓存就会被移除
# use_temp_path 临时路径，建议关闭，会有不必要的性能损耗
proxy_cache_path /opt/app/cache levels=1:2 keys_zone=blog_cache:10m max_size=10g inactive=60m use_temp_path=off;

server {
    listen 80;
    server_name localhost;
    location / {
        # 开启缓存，使用blog_cache zone
        proxy_cache blog_cache;
        proxy_pass http://blog;
        # 针对200和304请求进行缓存，缓存有效期为12h
        proxy_cache_valid 200 304 12h;
        # 其他状态的缓存有效期配置为10分钟
        proxy_cache_valid any 10m;
        # 维度配置
        proxy_cache_key $host$uri$is_args$args;
        # 增加头信息，告诉客户端缓存是否被命中
        add_header Nginx-Cache "$upstream_cache_status";
        
        # 当某台服务器出现error、timout、500状态等情况时，就跳过此台服务器
        proxy_next_upstream error timout invalid_header http_500 http_502 http_503 http_504;
        include proxy_params;
    }
}
```

## 如何清除缓存

* 清空对应缓存目录：`rm -rf 缓存目录内容`，无法清空指定的url缓存
* 使用第三方模块`ngx_cache_purge`

## 如何让部分页面不缓存

```nginx
# 定义不将响应保存到缓存的条件。如果字符串参数的至少一个值不为空且不等于“0”，则不会保存响应
Syntax:	proxy_no_cache string ...;
Default:	—
Context:	http, server, location
```

**示例：**

```nginx
# 以下配置在server块中
# 如果是登录、注册、密码重置等页面，就设置cookie nocachekey为1
if ($request_uri ~ ^/(url3|login|register|password\/reset)) {
    set $cookie_nocache 1;
}

location / {
    proxy_cache off;
        proxy_pass http://imooc;
        proxy_cache_valid 200 304 12h;
        proxy_cache_valid any 10m;
        proxy_cache_key $host$uri$is_args$args;
        add_header  Nginx-Cache "$upstream_cache_status";  
    	# 生效nocache
    	proxy_no_cache $cookie_nocache $arg_nocache $arg_comment;
    	proxy_no_cache $http_pragma $http_authorization;
    
        proxy_next_upstream error timeout invalid_header http_500 http_502 http_503 http_504;
        include proxy_params;
}
proxy_no_cache $cookie_nocache $arg_nocache $arg_comment;
proxy_no_cache $http_pragma $http_authorization;
```

## 分片请求

1.9版本增加了`slice size`提供了大文件分片请求的支持：

```nginx
Syntax: slice size;
Default: slice 0;
Context: http, server, location
```

1. 前端请求大文件，nginx去服务端获取文件大小
2. 根据定义的slice片的大小，nginx进行切片，分为多个请求，请求服务端

**优势**：每个子请求收到的数据都是一个独立的文件，其他请求不会受影响

**缺点**：如果slice大小设置的不合理（slice太小），会导致文件描述符耗尽等情况


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://yangsx95.gitbook.io/notes/distributed/web-fu-wu-qi/nginx/huan-cun.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.