Client body buffering with FastCGI

[Maxim Khitrov]

On Thu, Feb 17, 2011 at 12:05 PM, Maxim Dounin <mdounin at mdounin.ru> wrote:
> Hello!
>
> On Thu, Feb 17, 2011 at 09:48:24AM -0500, Maxim Khitrov wrote:
>
>> I'm trying to configure AjaXplorer, a PHP/Ajax file manager, to work
>> behind nginx 0.8.54 on FreeBSD 7.3. The problem I'm running into is
>> the inability to upload files more than ~64 MB in size. Ideally, I'd
>> like to bump that limit up to 1 GB. I realize that HTTP is not ideal
>> for this, but other transfer methods are not an option.
>>
>> PHP and nginx are both configured to accept 1 GB POST requests. As far
>> as I can tell, nginx buffers the contents of the entire upload to disk
>> before forwarding the request to the FastCGI process. This data is
>> then read from disk and written back to disk by PHP. The whole
>> write/read/write cycle is causing a timeout, first in nginx, and then
>> in the PHP process (though there may also be some other problem that I
>> haven't figured out yet).
>
> Setting bigger timeouts should help.  All timeouts in nginx are
> configurable (proxy_connect_timeout, proxy_send_timeout,
> proxy_read_timeout - and similar ones for other backend modules).
>
> Though it sounds strange that nginx times out while writing
> request to php as it should reset timer on any write operation.
> Timeout may happen after writing request (read timeout) - i.e. if
> php takes too long to process request, but you have to enlarge it
> anyway then.

I think the timeouts are a side effect; the problem seems to be
between nginx and the FastCGI unix socket. I just ran two quick tests.
All possible timeouts for PHP and nginx have been set to 60 seconds,
memory and POST size limits are at 1 GB.

First, I uploaded a 90 MB file. All went well - the upload finished in
~3 seconds, PHP took ~8 seconds to copy it to the final destination.
So 11 seconds total from the time that I hit 'upload' until I got a
success notification.

Next, I tried to upload a 100 MB file. The upload took ~4 seconds, but
then nothing... The server sat for 1 minute with CPU 100% idle. After
that, nginx timed out. I had these 2 messages in the error log:

2011/02/17 13:14:21 [warn] 68428#0: *8 a client request body is
buffered to a temporary file /srv/upload/tmp/0000000002
2011/02/17 13:15:25 [error] 68428#0: *8 upstream timed out (60:
Operation timed out) while sending request to upstream

As soon as the second message appeared, the PHP process began
executing, copying 20 MB of the uploaded data to the final
destination. The remaining 80 MB never made it. In my other tests, the
amount of data saved varied between 20 and 60 MB.

In other words, it looks like nginx receives the entire request and
begins writing it out to the FastCGI socket. After copying a portion
of the data, the transfer breaks. Nginx then times out and closes the
socket, which causes PHP to begin executing this partially received
request. I did verify that AjaXplorer code is not executed until the
nginx timeout, so this software is not the problem. The fault is
either with PHP, nginx, or the operating system.

Any ideas on what could be preventing the entire request from being
written out to the FastCGI socket? I have error_log set to 'debug',
but the two messages above is all I'm getting.

- Max