I've turned on the experimental SDCH compression protocol by default for the
".google.com" domain only.  Currently Google is helping to test support by
serving some web pages using this protocol (to browsers that support it), so
this default change will only impact search at google.com If things go well,
I'll enable it for the entire net in a week or two.

Please report bugs or problems with search if you see any.

The (new/current) default is equivalent to starting chrome via:

./chrome.exe -enable-sdch=.google.com

If this horks your build, and blocks you, you should run with an explicit
enable supplying a non-existent domain, such as:

./chrome.exe -enable-sdch=.nonexistantdomainthatyournotworriedabout.com

If you're testing out serving the SDCH protocol from your server (other than
*.google.com), you can fully enable SDCH support in Chromium via:

./chrome.exe -enable-sdch

FAQ

What is SDCH?  It is a delta-compression protocol.  The server provides a
dictionary, and then can send results "relative" to that dictionary.

Where can I read more about it?  Take a look at
http://groups.google.com/group/open-vcdiff/browse_thread/thread/8c4bf...

How does chromium support it (roughly)?  Chromium advertises its support of
"sdch" in its Accept-Content header (i.e., where it also says it supports
gzip, deflate, etc.).  A supporting server then sends back (in a response
header) an URL to get a dictionary "for future use."  Chromium gets the
dictionary about 15 seconds later (to avoid interfering with the current
download).  Chromium then advertises both support for "sdch" as well as its
possession of the dictionary to the appropriate domains.  A domain's server
that recognizes the dictionary then compresses future payload responses
using the delta-compression (commonly in concert with gzip compression).

My "rough" explanation below used the header name "Accept-Content" when (as
a coworker pointed out) the correct header name is indeed "Accept-Encoding."

If you're curious to see some evidence of this feature working (after doing
a google search), you can take a look at "about:histograms/Sdch" and you'll
see various stats about its activity (e.g., dictionary sizes and counts; pre
and post compression sizes (excluding gzip); etc.).
The rest of the email is hopefully more factual.

Jim