Subject: RE: [lemonade] COMPRESS Thoughts

From: "Burger, Eric" <[email-masked]>
Date: Tue, 13 Jun 2006 05:00:56 -0400

<chair-hat off>
Question: what is the round-trip latency to wait for the untagged OK?
If it is two round-trips at 750ms each, that would be "less than ideal."
If we have to wait a long time before we say "turn off compression,"
then I would offer that implementers suck it up.  Then again, that could
be the reason to say, "just compress everything."  :) 

-----Original Message-----
From: Arnt Gulbrandsen [mailto:[email-masked]] 
Sent: Thursday, June 01, 2006 6:31 AM
To: [email-masked]
Subject: Re: [lemonade] COMPRESS Thoughts

Eric Burger writes:
> (4) Protocol allows for client to turn it on or off at will (not per 
> body part, but point in time in session)

There's a performance gotcha to this, I realized while changing my 
daughter's nappies at 6am this morning.

The compression library likes to read in big chunks. Everyone likes to 
do I/O in big chunks. Reading network input one byte at a time is such 
a performance drag. If the client tells the server that starting with 
the next command, its commands are uncompressed, the server's 
compression library has to stop reading at the right byte. It can't 
simply read all it can eat. Ditto for responses.

This should fix it:

1. The client cannot send any other commands until the server has sent a

tagged OK for the 'disable upstream compression' command.

2. The server disables compression after sending the tagged OK for that 
command (including the CRLF).

3. The server cannot send any unsolicited responses after sending that 
tagged OK and before receiving the next command.

The last introduces a new server mode and gets in the way of extending 
IDLE... right now, I think that server mode is more trouble than it's 
worth.

What is the problem if compression stays on once it's turned on? I can't

recall any relevant problems with STARTTLS, which behaves that way.

Arnt

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