求教cache-control头的控制（影响了自己写的缓存功能了）
自己做了一个php控制的缓存，依靠etag和文件缓存来处理
如果浏览器发送了etag，则进行对比，etag一致，直接发送304，etag不一致，如果有文件缓存，则直接读取文件缓存，并发送当前服务器缓存的etag
（文件缓存和etag的更新在其他地方处理）
现在突然发现有响应没有返回304，一查，发现这个地址的服务器http响应头返回了cache-control:no-cache
我清空服务器的缓存后看，第一次响应的时候服务器就自动发送了一个no-cache头，（我的etag也发送了出去的），结果就是无论服务器端有没有缓存，浏览器都不会把etag添加到自己的请求头里面去，服务器端处理的时候没有收到etag，就当做是第一次请求，然后又重新读取文件缓存，又重新发送etag……（响应200）
大致是这么回事，但是这样就失去了我想用304来直接缓存的效果了。
看了一下区别，正常的数据，大概10KB，运行一直正常（没有缓存初次请求130ms，有缓存初次请求90ms，之后16ms或以下）
而没有发送304的这个（一直发送no-cache）的这个，数据只有304B，（但是就算不加缓存模块，因为服务器计算的原因，也要花90ms左右），
怀疑是不是因为数据返回不一致的原因而导致的，将这个304B的数据扩增到12KB，还是发送no-cache头，增加到20kb，也是一样的。
然后懵了……不知道怎么回事了。
（天地良心，代码全部是我写的，除了一个header(etag)外绝对没有发送其他的etag了）
回复讨论(解决方案)
找到原因了……
原因是什么？
为什么会一直发送no-cache呢？估计是服务器设置了吧。
原因是什么？
为什么会一直发送no-cache呢？估计是服务器设置了吧。
php的session-limit的原因
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