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From Lynn Schaper <scha...@Colorado.EDU>
Subject Re: [users@httpd] MaxRequestsPerChild, memory, and ps allocation
Date Mon, 02 Jun 2003 18:30:38 GMT
The code does use move_uploaded_file; beyond that we need to research
with the IMP developers.

In the meantime, we will probably still add a workaround in apache,
since we want to be sure that we don't run out of memory with large
processes.  Does anyone have answers/suggestions to these questions:

1) When we have "MaxRequestsPerChild 10000", we've seen the children
serve up to 700 more than 10,000 requests.  Here are 2 lines (Request
eliminated) from fullstatus on one pid, the last one is where it died
at 10622 requests:
   16-2 10077 0/10622/18191 _ 674.74 1 411 0.0 21.94 38.59 12.203.214.9
   16-2 10077 0/10622/18191 W 674.74 4 0 0.0 21.94 38.59 127.0.0.1

QUESTION: How often does the apache parent check to see if a child has
reached its limit?  How far over the MaxRequestsPerChild can we normally
expect to see the children run


2) Apache seems to favor certain children when the server is not busy.
At some times of day, we have many children that are idle, and apache
does not seem to distribute requests to all children, rather it uses its
"favorites."  When we look at children that were started at the same
time, some have taken 4000 requests, others only 2000 requests, and
corresponding amount of data transferred and CPU time also vary.  It
makes sense that the "favorites" are the ones that suck up memory, since
they serve more requests and thus are more likely to do attachments.

Here are some lines from fullstatus (Request eliminated), sorted by
number of accesses this child:

7-0 21928 0/4003/4003 _ 272.62 28 0 0.0 24.90 24.90
17-0 21938 0/3969/3969 _ 268.34 5 0 0.0 22.02 22.02
snip
26-0 23713 0/2111/2111 _ 152.87 5 0 0.0 12.20 12.20
27-0 23739 0/2036/2036 _ 145.91 4 2386 0.0 12.74 12.74

QUESTION: Is there a method to this?  What is the reasoning?  We can
tune the server to not have as many idle servers around, but why doesn't
apache use the ones that are there and idle?  It seems to use the same
5-10 (when we're not busy) over and over again.

Thanks,
Lynn
--
    Lynn Schaper                        Schaper@colorado.edu
    Information Technology Services     Central and Unix Services     
    University of Colorado at Boulder   303-492-3872

> On Fri, 30 May 2003, Lynn Schaper wrote:
> > Our testing shows that these processes grow when users upload and send
> > attachments, and for some reason the memory is not released after that
> > connection is finished.  We can accept that as a PHP feature/bug
> 
> It used to be the case that PHP we buffer an entire upload in ram before
> writing it out to disk.  But that was fixed a while ago, and the fix is
> most definitely in the version you are using.  I would have a look at the
> user-space code that manipulates the uploaded file.  Perhaps it is reading
> the entire thing into memory in order to copy the uploaded file out of the
> tmp dir and into its final location.  The code should be using the
> move_uploaded_file() function to do this.  That will simply do a rename()
> (if possible) and if that fails it will try to copy it in 8k chunks.
>
> If your code is already using move_uploaded_file(), then have a look at
> what is being done with the file once it has been moved into the right
> location.  It sounds a lot like you have a basic application-level problem
> where something is loading the entire file into memory at some point.
>
> I realize your question was regarding workarounds and not the problem
> itself, but I much prefer to try to solve the real problem.
>
> -Rasmus

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