SDCH turned off by default???

[Yoav]

Hi,

I was running some SDCH tests with both Chrome 9 and IE's Google
toolbar on windows, and saw that both stopped advertising "Accept-
Encoding: sdch" in their requests.
I also tried sending "Get-Dictionary" Header field in the response to
chrome, but that did not trigger a request to fetch the dictionary.
When running chrome with the "-enable-sdch" flag, "Accept-Encoding:
sdch" request fields are sent as before.
Was SDCH turned off by default? If so, are there plans to return it to
the defaults? And why was it turned off?

Thanks,
Yoav Weiss
------------------
http://yoav.ws

[Wei-Hsin Lee]

Hi,

SDCH feature is disabled on IE toolbar. But it should be on in Google Chrome. I was under the impression that it is not on for the first search request.

Thanks,

Wei-Hsin

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[Yoav Weiss]

I believe that this is in fact what happened. I ran some weird experiments that probably caused the browser to stop trying. I just didn't verify beforehand it sends sdch Accept headers, so when they were gone after the experiments, I falsely assumed they were never there.

I restarted the chrome instance and now it seems like it is working.

Thanks a lot!

Yoav 

On Thu, Feb 24, 2011 at 9:13 PM, Jim Roskind <j...@google.com> wrote:

SDCH has not been turned off.

SDCH does monitor the channel, and detect corruption.  If there is a problem, then it will disable itself in your instance.  The "disable" is really an exponential backoff, so it will try again... but at progressively longer intervals.

Here at Google, if you visit the internal pages which show rooms in buildings, the URL will have the form "http://....google.com/search/..."  Sadly, this looks exactly like a GWS URL (or at least exactly as defined in the dictionary you get from GWS!  As a result, when Chrome advertises SDCH (with a dictionary as well!!!), and then does not get an SDCH compressed payload back, it automatically turns of SDCH (or starts the back-off process).

To better see what is going on in your instance of chrome, visit:

about:histograms/Sdch3.

That will show a variety of histograms, including sizes of Dictionaries that YOU downloaded, times for some SDCH transactions YOU made, etc.  One interesting one is:

about:histograms/Sdch3.FilterUseBeforeDisabling

It will tell how many SDCH transactions took place before it was disabled (for some period of time).

Hopefully the slightly cryptic names can be deciphered to get a slightly better perspective of what is going on.

Also note that if you restart Chrome, you'll have a "clean slate," so you can then do a google search (advertising SDCH), allow Chrome to download the dictionary (about a second later... and often from disk cache), do another Google search (which will advertise SDCH and the dictionary), and you'll get an SDCH compressed result.

Jim