APC，磁盘命中以及要求/包含 [英] APC, disk hits, and requires/includes

问题描述

一个非常简单的问题，但我实际上不能确定. PHP如何处理APC已缓存的文件的需求/包含?我的理解是，该缓存主要是节省了PHP来编译已经缓存的文件，但是对我来说还不清楚是否还保存了查找/获取文件所需的磁盘命中.是吗?还是即使操作码已经被缓存，PHP还是会击中磁盘，唯一的区别是它不会再次执行编译过程?

Pretty simple question, but I can't actually tell for sure. How does PHP behave with requires/includes of files that have been already cached by APC? My understanding is that this cache primarily saves PHP of compiling a file that has been already cached, but it's not clear to me whether it also saves the disk hit necessary to find/fetch the file aswell; so, does it? Or will PHP hit the disk, even if the opcode has been already cached, the only difference being that it doesn't do the compilation process again?

我想认为需求/包含神奇地知道了文件已缓存，因此多亏了APC，因此可以直接从内存中获取文件，但是我只是意识到我没有理由假设情况如此，所以我问为什么.

I would like to think requires/includes magically know a file is cached and thus fetch it directly from memory thanks to APC, but I just realized I have no reason to assume this is case, hence why I ask.

推荐答案

APC覆盖了Zend Engine中的zend_compile_file函数，该函数除其他功能外还负责查找和打开实际文件；因此，如果文件已经被缓存，它能够在磁盘命中之前劫持"磁盘命中.

APC overrides the function zend_compile_file in the Zend Engine, which among other things is responsible locating and opening the actual files; thanks to this it is able to "hijack" disk hits before they happen if the file is already cached.

因此，是的，如果文件被缓存，则会从内存中提供文件.

Therefore, yes, files are served from memory if cached.

来源: APC技术说明和Zend Engine源代码，特别是 zend_language_scanner.c

Sources: APC Technotes and the Zend Engine source code, specifically zend_language_scanner.c

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