为什么file_get_contents比memcache_get更快？ [英] Why is file_get_contents faster than memcache_get?

问题描述

我使用file_get_contents从磁盘加载XML文件，作为一个测试，我发现我可以在3.99秒内使用 file_get_contents（） 1,000次加载156K文件。我已经子类化了加载的部分，并用一个memcache层替换了它，在我的开发机器上发现我可以在4.54秒内完成1000个相同文档的加载。

<我明白，file_get_contents（）会做一些缓存，但它看起来实际上比知名的缓存技术更快。在单个服务器上， file_get_contents（）的性能是否可以达到？

我是在PHP 5.2.17通过Macports，OS X 10.6.8。

编辑：我发现这个尺寸的XML文档，有一个小的好处，在使用 MEMCACHE_COMPRESSED 标志。通过内存缓存的1500次加载是在6.44秒（压缩）而不是6.74（没有）的情况下完成的。然而，两者都比 file_get_contents 慢，它在5.71秒内完成相同数量的加载。

解决方案

因为file_get_contents mmap 这个文件，所以你只会有几个文件系统调用，这将最终在文件系统缓存中。 memcache涉及对memcached的进程外调用（并且在集群实现中离开服务器）。
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file_get_contents（）关键取决于文件系统的类型，例如NFS挂载的文件系统上的文件没有被映射，并且这个访问可能会很慢。同样在多用户服务器上，文件系统缓存可以被其他进程快速刷新，而memcached缓存几乎肯定会在内存中。

I'm loading XML files from disk using file_get_contents, and as a test I find I can load a 156K file using file_get_contents() 1,000 times in 3.99 seconds. I've subclassed the part that does the loading and replaced it with a memcache layer, and on my dev machine find I can do 1000 loads of the same document in 4.54 seconds.

I appreciate that file_get_contents() will do some caching, but it looks like it is actually faster than a well-known caching technique. On a single server, is the performance of file_get_contents() as good as one can get?

I'm on PHP 5.2.17 via Macports, OS X 10.6.8.

Edit: I've found on XML documents of this size, there is a small benefit to be had in using the MEMCACHE_COMPRESSED flag. 1,500 loads via memcache are done in 6.44 sec (with compression) rather than 6.74 (without). However both are slower than file_get_contents, which does the same number of loads in 5.71 sec.

解决方案

Because file_get_contents mmaps the file and so you'll only have a few file system calls and this will end up in the file system cache. memcache involves out-of-process calls to the memcached (and out of server on a clustered implementation).

The performance of file_get_contents() crucially depends on the type of file system, for example a file on an NFS mounted file system is not mmapped and this access can be a LOT slower. Also on a multi-user server, the file system cache can get rapidly flushed by other processes whereas the memcached cache will almost certainly be in memory.

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