[plt-scheme] Servlet Timeouts

From: Matthias Felleisen (matthias at ccs.neu.edu)
Date: Fri Jul 2 16:56:37 EDT 2004

It depends on what you mean by "production". Some of us use
the web server for hosting web sites that service a fair number
of people and are critical to their work. Even though it does
break on occasion -- like all software, it has served us well.
[fair number is a dozen or a few dozens or so]

Having said this, if you are about to create Amazon 2, I'd
suggest that you don't use the plt server just yet.

-- Matthias

On Jul 2, 2004, at 11:38 AM, Arend P. van der Veen wrote:

>  For list-related administrative tasks:
>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> Hi,
> If I understand correctly, you are saying that some of the memory PLT 
> Scheme requests from the operating system is not freed.    So am I 
> correct in concluding that if I run a production web server for a long 
> period of time it will eventually run out of memory ?  If this is the 
> case are there any work arounds ?
> Thanks in advance,
> Arend van der Veen
> Greg Pettyjohn wrote:
>>  For list-related administrative tasks:
>>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>> There is a servlet timeout test as part of the servlet test suite.
>> I will be improving these tests in the next week or so.
>> Pete Hopkins, a student at Brown, has also done a series of stress 
>> tests which characterize the server's
>> resource usage with respect to continuations.
>> We have identified a few problems with managing the lifetimes of 
>> continuations and
>> will be providing a solution in  some future version of the server.
>> Although this is a research project that we are currently 
>> aggressively pursuing, we
>> are still only a few weeks into it and I don't yet have a prediction 
>> as to when a solution will
>> be available.
>> On Jul 1, 2004, at 8:16 AM, Arend P. van der Veen wrote:
>>>  For list-related administrative tasks:
>>>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>>> Hi,
>>> I have been attempting to test the servlet timeout feature to 
>>> confirm that the system reclaims continuations used by a servlet.  
>>> To perform this test I wrote a function (in Python) on another 
>>> machine that accessed the add.ss example servlet.  The function 
>>> submits the first number but never submits the second number.  I 
>>> call this function 40,000 times.  According to my web server 
>>> configuration file I would expect that the servlet should time out 
>>> in two minutes (default servlet timeout = 120 seconds).   After I 
>>> completed my test the web server process has consumed about 152 MB 
>>> of RAM.     I think that the memory consumption has stabilized even 
>>> if I rerun the test (and not restart the web server).  Also, it 
>>> takes much more then 2 minutes for my python client to access the 
>>> server 40,000 times.
>>> 1.   I was originally having problems with the add servlet leaking 
>>> memory.  I included a send/finish at the end of the unit.  My new 
>>> add.ss is at the end of this post.  Am I correct in assuming that 
>>> this servlet should not leak memory now ?
>>> 2.   Do the log files contain any information indicating that a 
>>> servlet has timeout ?  I was not able to find any indications.
>>> 3.   When the servlet times out should all the RAM associated with 
>>> the servlet be automatically released ?
>>> Thanks in advance for your help.
>>> Arend van der Veen
>>> add.ss:
>>> (require (lib "unitsig.ss")
>>>         (lib "servlet-sig.ss" "web-server")
>>>         (lib "servlet-helpers.ss" "web-server")
>>>         (lib "date.ss"))
>>> (unit/sig () (import servlet^)
>>>  ; request-number : str -> num
>>>  (define (request-number which-number)
>>>    (string->number
>>>     (extract-binding/single
>>>      'number
>>>      (request-bindings (send/suspend (build-request-page 
>>> which-number))))))
>>>  ; build-request-page : str -> str -> response
>>>  (define (build-request-page which-number)
>>>    (lambda (k-url)
>>>      `(html (head (title "Enter a Number to Add"))
>>>             (body ([bgcolor "white"])
>>>                   (form ([action ,k-url] [method "post"])
>>>                         "Enter the " ,which-number " number to add: "
>>>                         (input ([type "text"] [name "number"] [value 
>>> ""]))
>>>                         (input ([type "submit"] [name "enter"] 
>>> [value "Enter"])))))))
>>>  (define (answer-page)
>>>    `(html (head (title "Sum"))
>>>         (body ([bgcolor "white"])
>>>               (p "The sum is "
>>>              ,(number->string (+ (request-number "first") 
>>> (request-number "second")))))))
>>>  (send/finish (answer-page)))

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