[RESOLVED] Unable to request more than one resource from Apache simultaneously

cbj4074

Hello,

This must be a common problem, but I'm shocked at the sparsity of comments regarding it.

Suppose that I have a PHP script that performs some rather file-intensive operations, which may take several minutes to complete. Or, suppose that I am downloading a sizable file (that was passed to Apache via PHP-sent headers) that may take an hour to download.

In either of those scenarios, I am unable to open another browser window (or tab) and continue browsing another area of the same website.

This problem occurs both on localhost (Windows 7 with Apache 2.2 and PHP 5.2) and on a remote, hosted copy of the same site (CentOS 5.0 Final with the same versions of Apache and PHP).

These other threads may be relevant and related to my issue:

http://phpbuilder.com/board/showthread.php?t=10224788

http://phpbuilder.com/board/showthread.php?t=10335002

http://phpbuilder.com/board/showthread.php?t=10344880

I attempted to receive assistance from my hosting provider, mediaTemple, but they responded with "???", in effect. Here is the ticket:

Hello,

Whenever I attempt to download a large file from my (dv) server, I am unable to do anything else on the site. I can't even navigate away from the page, let alone start a second download.

I understand that this behavior is desirable in certain circumstances (such as to prevent DoS attacks), but it's killing my application here. I need Apache to be able to service at least two simultaneous requests from the same IP address, for files of any size.

Based on what I've read at the following locations

http://forums.digitalpoint.com/showthread.php?t=1284915

http://serverfault.com/questions/125168/apache2-limit-simultaneous-requests-throttle-bandwidth-per-ip-client

http://www.webhostgear.com/279.html

it seems that Apache's DEFAULT behavior is to service as many simultaneous requests from a given IP as is possible. As such, I am wondering if (mt) has implemented some type of module to change that behavior, and if so, if that module can be configured to behave differently (or disabled altogether in favor of something like mod_limitipconn.c, as described in the webhostgear.com article above).

Thank you for your help.

I would greatly appreciate any guidance on the matter, and thank you in advance for your time.

dagon

if it happens local host and remote host, you cant expect your hosting company has done anything to cause it. Can't say i have ever encountered this before. if you remove all of your site overhead and just set up a single page to stream a file, can you hit that page twice? Is there anything in the error logs or apache access logs of any help?

bradgrafelman

cbj4074 wrote:
I am unable to open another browser window (or tab) and continue browsing another area of the same website.

Sounds like a browser or OS issue rather than PHP, Apache, or the host. Are you using IE?

Also, I have a couple of sites hosted by MediaTemple and have never experienced this issue. :p

dagon

you could post links to your site and we could 'play' with it.

cbj4074

Much thanks for the prompt replies.

bradgrafelman, the problem occurs in Firefox, Chrome, and IE (I've only tested it on Windows thus far).

dagon, I know. I wasn't necessarily implying that they did anything to cause it; my thinking was more along the lines of, "Maybe my local Apache server is configured similarly to my host's; they're the experts, so maybe they know what's causing it in both places." Opening a support ticket was somewhat of a last resort, as I've looked high and low for an explanation. Given that two of the most seasoned people on this board (you and bradgrafelman) don't have an off-the-cuff solution, it seems not to be a widely-discussed issue. I can't be the only one; my setup is pretty "stock" in all respects.

Sure, I can give you access to some test material... buy an album on http://indietorrent.org (may I recommend http://indietorrent.org/alpharev ?) =). You could buy a song, but the file would probably be too small with which to test (unless you throttle your connection in some way). I could also throw another "test file" of sorts up on the site, such as a GNU/Linux ISO or similar. I can get to work on that if it sounds like a worthwhile option.

I should also mention that this happens no matter how the file is presented to the browser. In other words, this problem occurs whether I "pass the file from PHP to the browser via header()" or whether I provide a "direct HTTP link" to a static file that exists within the webserver's document root. Further, the problem happens on both of my hosted mediaTemple boxes; one is a (gs) (low-end POS, essentially) and one is a mid-range (dv) (CentOS 5.0 Final with Plesk 8.3).

Thanks again for your responses, guys. Looking forward to any additional thoughts you might have.

dagon

i can stream\play all the previews simultaneously for any album (or several at a time in different tabs) (sounds like chaos) but that indicates its working as expected to me.

cbj4074

Hi, dagon, thanks for testing it out.

Those clips are encoded at 80kbps, and therefore 500-600KB each. As such, when you play each clip, it's likely downloaded to your machine almost immediately. With such small files, I'm not sure that we're reproducing the issue.

I've placed a Ubuntu CD image at the root of the domain; do you mind trying to download that in two separate tabs simultaneously? Here is the URL:

http://indietorrent.org/ubuntu-10.04-desktop-i386.iso

The interesting part is that I am able to download two copies of the file simultaneously if I use two different browsers (on the same computer). So, it seems reasonable to conclude that the "blocking" is not based on IP address.

Thanks again for all of your help; it truly is appreciated.

dagon

i got two copies downloading in one browser, using half my bandwidth each, i launched 4 tabs, the other two never started. Not sure what that says 🙁

cbj4074

Oh, boy. That just muddies the waters even further! :eek: Thank you for adding more test-case data to the stack.

bradgrafelman (or any other curious party), do you mind giving it a whirl at your convenience, and confirming whether or not the results are consistent with dagon's?

dagon

6 copies simultaneously downloaded to one of the work servers

cbj4074

Okay, so based on that information, what the heck's going on?

Are our personal workstations limiting the number of simultaneous outgoing connections? Our routers (or other networking devices)?

cbj4074

So, all this time later, I finally determined what was happening here.

There were two issues at play:

1.) The fact that some browsers limit the number of simultaneous connections to a remote host, and;

2.) The fact that I had neglected to close the PHP session with session_write_close() before performing the intensive operation, thereby causing a session file lock that was queuing subsequent PHP page requests that required access to the same session.

I had always thought that this issue was a browser or Apache issue, and not a PHP issue. So, I'd been looking for answers in all the wrong places.

My other thread, "[RESOLVED] Session data failing to be saved", describes the solution:

http://phpbuilder.com/board/showthread.php?t=10377230