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I'm trying to set up a coldfusion server to accept uploads of large files, and I'm bumping into some limits. Here's what I've observed so far:

There are two settings in ColdFusion Administrator that limit the size of uploads: "Maximum size of post data" and "Request Throttle Memory". If the size of your upload (including HTTP overhead) is bigger than either one of those settings, the upload is rejected. I can't figure out why we need 2 of these; whichever one is set higher doesn't have any effect as far as I can tell. The lower one wins.

When someone tries to upload a file that's too big, they don't get a nice error message. The upload just hangs forever after sending about 1 TCP window worth of data. And it hangs in a really bad way. Even after the client gives up and disconnects, the associated apache thread is still tied up (I can see this using mod_status). The stuck threads just keep building up until there are none left to take new requests and the server has to be restarted.

The "Request Throttle" is a thing I really don't understand. All documentation about it speaks of it as the size of a memory region. If that's what it is, then I can't see how it's related to file sizes. It hints at something I just don't want to believe: that ColdFusion slurps the entire uploaded file into memory before writing any of it to disk. No sane person would do that, when an upload loop (read a medium-sized block, write it to disk, repeat until finished) is so easy. (I know the structure of an HTTP multipart/form-data post makes it a little bit harder but... surely a big company like Adobe with a web development product can get this right... can't they?)

If whole-file slurping is actually what's going on, how do they expect us to choose a workable size limit? Allow a gigabyte and a few simultaneous users can run your server out of memory without even trying. And what are we going to do, not allow gigabyte uploads? People have videos to post and no time for editing them!

ADDTIONAL INFO

Here are some version numbers.

Web server:

Server: Apache/2.2.24 (Win64) mod_jk/1.2.32

ColdFusion:

Server Product           ColdFusion
Version                  ColdFusion 10,285437
Tomcat Version           7.0.23.0
Edition                  Enterprise
Operating System         Windows Server 2008 R2
OS Version               6.1
Update Level             /E:/ColdFusion10/cfusion/lib/updates/chf10000011.jar
Adobe Driver Version     4.1 (Build 0001)

ADDTIONAL INFO #2

I don't know why you'd want to know what values I've put in the limit fields, but they were both set to 200 MB for a while. I increased "Maximum size of post data" to 2000 MB and it didn't have an effect. I already figured out that if I increase "Request Throttle Memory" to 2000 MB it will allow a larger upload. What I'm looking for here is not a quick "stuff a bigger number in there!" answer, but an detailed explanation of what these settings actually mean and what implications they have for server memory usage.

Why the server thread stalls forever instead of returning an error message when the limit is exceeded could be separate question. I assumed this would be a well-known problem. Maybe I should ask first if anyone else can reproduce it. I've never seen a "file too large" error message returned to a client from ColdFusion. Is it supposed to have one?

ADDITIONAL INFO #3 Some experimentation has led me to a partial answer. The first thing I was missing was that "Request Throttle Memory" (RTM) does something useful if it is set higher than "Maximum size of post data" (MSOPD). In my first round of tests, with no clue about the relationship between them, I had them the other way around. With my new understanding, I can see that the ratio RTM/MSOPD is the number of simultaneous uploads that will be allowed if they are all near the maximum size.

Assuming that the "Request Throttle Memory" is actually a memory buffer, and not a temporary file, this means that my worst fears were correct. Every file is kept entirely in memory for the full duration of its upload. Nobody has said anything to make me believe otherwise (although I also don't see anyone jumping up to say "yes, they did this stupid thing")

Also with this new understanding, the stalled uploads make some sense. The server doesn't have memory available to accept the upload, so it just doesn't read from the socket. The TCP buffers fill up, window size becomes 0, and the client waits it to open up again, which should happen as soon as the server starts reading the request. But in my case, for some reason, that never happens. The server forgets about the request entirely so it just lingers.

The case of "Maximum size of post data" being hit is still a bit of a mystery. Requests that hit a hard limit shouldn't be queued, just rejected. And I do get a rejection message ("Post Size exceeds the maximum limit 200 MB.") in server.log. But again in this case the server seems to forget about the request without ever sending an error to the client.

share|improve this question
    
Two questions: 1. Are you sure it's Cold Fusion, and not the web server itself? and 2. Have you looked at the request timeout? –  Katherine Villyard Mar 14 at 21:04
1  
I'm sure. There's no timeout (the upload fills one TCP window and then stalls. Proven with wireshark. Chop a few bytes off the end of the file and it sends in 13 seconds.) And I can post an upload to a static HTML page and it sends fine (it doesn't get saved anywhere because there's nothing processing the form data, but the point is it doesn't stall.) –  Wumpus Q. Wumbley Mar 14 at 21:09

2 Answers 2

up vote 2 down vote accepted

I will also try to explains the settings for tuning:-

  • Maximum number of POST request parameters - This refers to the maximum number of attributes/parameters sent over a particular request. Used particularly, while posting data on a form.
  • Maximum size of post data - This is the maximum data which can be posted on a server. This is the sum of all the data in a particular form during a POST request.
  • Request Throttle Threshold - ColdFusion can throttle (forcefully slow down) incoming requests if needed. However, really small requests (those with a small payload) can be allowed through regardless of the throttle state. To allow small requests to be processed, specify the maximum allowed size (the default is a maximum of 4 MB).
  • Request Throttle Memory - To throttle requests, specify the maximum amount of memory allocated for the throttle. If not enough total memory is available, ColdFusion queues requests until enough memory is free (the default is 200 MB). It wou;ld not reserve the memory for Req1, as its lower than Threshold.

Consider that there are three simultaneous requests Req1 (3 MB), Req2 (6 MB) and Req3 (9 MB). With the default settings, Request Throttle Threshold set to 4MB, ColdFusion will reserve (6+9=15MB) in the Throttle Memory. Likewise, it would keep on adding the Request Throttle Memory for all simultaneous requests and the limit is what we have set for Request Throttle Memory (default is 200 MB)

Hope this helps.

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This is similar to all the other descriptions I found through google. All of them omit the one thing I needed to know: that Request Throttle Memory is supposed to be bigger than Maximum size of post data. And I'm also only guessing that Request Throttle Memory must be smaller than JVM Heap Size, making it impossible to upload truly large files (near to or bigger than your server's RAM) in parallel. Nevertheless this is the best answer so far, so I'm upvoting it and I'll accept it if nothing else happens before bounty is up –  Wumpus Q. Wumbley Mar 19 at 14:15

You can use cftry-catch to capture the error and show a custom message to your users. Having said that, what are the values set for Maximum number of POST request parameters, Maximum size of post data, Request Throttle Threshold and Request Throttle Memory. Are you using CF Std or Ent and what is the version of ColdFusion?

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It is not possible to catch the error with cftry. The connection hangs without ever executing the first line of the cfm. (I put a cflog there to find out if it got that far and it didn't.) I will add some version information to the question. –  Wumpus Q. Wumbley Mar 15 at 2:27
    
"File too large" error message is usually thrown by the webserver, not ColdFusion. If you didn't find any thing in the CF logs, then please check the Event Viewer logs. There would be surely some reference to the error. Did you try "LimitRequestBody" from Apache. You can specify the filesize at webserver end as well. –  Anit Kumar Mar 17 at 21:43

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