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From Drew Kidder <Andrew.Kid...@Tivoli.com>
Subject Document cacheing - the story thus far.
Date Wed, 27 Sep 2000 14:06:16 GMT
Thank you all for your many suggestions.  However, none of them have worked 
as of yet.  Let me explain the symptoms one more time, in case we're 
barking up the wrong tree.  Here we go...

I have a servlet, which "manually" sends the file to the browser when a 
particular link is clicked.  I am writing a 4MB buffer, and writing to an 
OutputStream. If the user wants to throttle his download connection, I 
first cut the buffer size to 500K, and then use the Thread.sleep(2000) 
method after ever write to slow the process down a bit and allow other 
things to go on.

Now, when I click on a link with download throttling disabled, a .pdf file, 
it takes like 0.5 seconds for the "open it/save it" dialog box to 
appear.  If d/l throttling is enabled, and I click on the same link, it 
takes maybe 2-3 seconds for the "open it/save it" box to appear, but the 
actual sending of the file is done at the same rate as the non-throttled 
download.  What this says to me is that Tomcat or Apache is caching the 
file in the background (at my slower rate), and then independently 
returning the file on it's own.  This is obviously not the desired 
behavior, as this method makes it look as if the server is slow, rather 
than a controlled download slow-down.

The things I have already tried in an effort to fix this problem:

1.  If "throttle" is on, use HttpServletResponse.setBufferSize(0) to turn 
off the buffering.  [DOESN'T WORK]
2.  If "throttle" is on, use HttpServletResponse.setHeader(...) to set all 
the headers related to chacheing to "off" or "no-cache" or whatever.  [BUPKIS]
3.  flush() the output buffer after every write.  [ZIPPO]

So, if I want to have complete control over how fast that file gets sent to 
the client, is this buffer resizing thing going to do the job?  Or are 
there things that Tomcat/Apache thinks that it can do better, and the 
actual file transfer is out of my hands?

Thanks again for all your ideas and help.  This has now become sort of a 
personal mission to figure out what the heck is going on in Tomcat's brain 
and how it interacts with the browser. I'm going to figure this out, if it 
kills me.  :)

------
Andrew Kidder
L3 SW/Support Engineer, IBU
Tivoli Systems

512-436-4544
akidder@tivoli.com
http://www.tivoli.com



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