Any documentation about how Apache handles file up

问题:

I've spent hours googling, as well as searching the Apache site, and I can't find any documentation about how Apache handles file uploads — particularly large ones. I've read anecdotal reports that PHP isn't involved until the upload is complete, which is what I'd expect. But as far as what Apache does during the upload, I can't find anything.

The reason I'm hot for documentation is that Apache is storing uploads entirely in memory, instead of streaming them to disk. httpd will use every byte of available memory on the server I'm using until it crashes. Typically the amount of physical memory consumed is 3x the size of the file being uploaded, and increases in the vicinity of 5 MB/s (nowhere near my upload speed).

I've tested this same request on another LAMP stack I'm using, and Apache memory usage doesn't change at all throughout the course of the upload.

Can anyone explain to me how Apache could handle the same upload so differently on two different servers? Any thought greatly appreciated.

回答1:

Technically, PHP is handling the upload on behalf of Apache, and buffering the file in ram until it completes. However, your script will not gain control until after the upload completes (or aborts). Apache by itself won't buffer out to disk unless it has to. Think of it as an invisible "handle_upload()" function call that's transparently inserted as the very first thing in your script.

Back in the "everything is a cgi script" days when language interpreters like PHP weren't embedded in the webserver process, POST data was sent to the CGI script via standard input The file would pass through Apache directly to the CGI process and could be read byte-by-byte as it came in.

回答2:

The answer is unsatisfying. I never found any documentation.

I continued poking around in the dark, finally stumbling on a mod_fcgid upgrade (from 2.2 to 2.3.6) that did the trick. Perhaps there was a bug in 2.2.

The memory usage still goes up in 2.3.6, but far less dramatically. Only a few megabytes for a ~100 MB file. (However, when the upload finishes and the file is moved, memory usage instantly shoots up ~100-200 MB, but then seems to be immediately released.)

回答3:

This might help you, because the WAMP server has Apache in it.

http://www.wampserver.com/phorum/read.php?2,39439