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From Noah <s...@onastick.net>
Subject Re: [users@httpd] Delivering huge documents
Date Thu, 10 Mar 2005 00:56:00 GMT
On Wed, Mar 09, 2005 at 11:02:28AM -0800, Richard Crawford wrote:

> We have a document which is a 1.5MB PDF document.  For some of our 
> visitors, the download seems to stop before the full document is 
> delivered.  I haven't been able to identify any common issues among the 
> visitors who are having the problems (though I suspect they're on a 
> dialup connection).  The PDF itself seems to be have no problems, since 
> it's delivered just fine over broadband connections.  This issue appears 
> to be browser-independent as well.  I've also confirmed that the 
> affected users are using the most recent version of Acrobat Reader as well.

My first suggestion is to look at your network and rule out the obvious;
problems with large file transfers are often caused by duplex
mismatches. Check your upstream switch stats for collisions on the port
your host is on. Linux's 'ifconfig' will also show you collisions (if
you're on linux). I'd expect the issue to affect all downloads of the
large file, but it's still good to rule out the easy stuff. =)

Does this affect other protocols as well? For instance, transferring large 
files over FTP? Trying running an FTP server on the same box and serve the 
same file to a client machine that exhibits this behavior. If the same thing 
happens, it's not an application issue, so you get to start poking at things 
from a network perspective. Does the transfer just stop dead, or does it slow 
down over time and /then/ stop?  In either case, you may should consider finding 
a client that exhibits this behavior, sniffing the packets with tcpdump. Something 
like: 

    tcpdump -s 1500 -w sniff.pcap port 80 and host $remote_ip
    
...where $remote_ip is the IP of the client.

Poke at the resulting file in ethereal (with TCP sequence analysis
on; Edit->Preferences->Protocols->TCP) and see if you're
restransmitting packets. You may also want to check out TCPTrace
(http://www.tcptrace.org/).

--n

-- 
<huey> dd of=/dev/fd0 if=/dev/flippy bs=1024
<huey> ^^^ Making Flippy Floppy


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