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Re: [tor-talk] memory cached pages should reload instantly-but DON'T

On 5/7/2013 10:56 PM, David Vorick wrote:
Are we sure this is a bug? Even when a page is in the cache doesn't it have
to communicate with the server to verify that the cache hasn't expired?
Perhaps this is what you are experiencing.

On Tue, May 7, 2013 at 9:41 PM, Tom Ritter <tom@xxxxxxxxx> wrote:

Hm, that's an tough question.  TBB doesn't modify the FF code very
much at all, and the patches are pretty lightweight - they're all
listed here:
although some of them do deal with caching.

The about:config settings are all listed here (AFAIK):

so I wonder if there's anything in there you might recognize as
causing a problem?

I'm afraid I'm not quite sure that the issue could be, these types of
bugs are pretty tricky to track down.  I did want to point you in the
right direction for maybe finding the culprit though.

I looked at torbrowser.git from link above. One interesting thing. They show on line 16 pref("browser.cache.disk.enable", false); - but in my brand new extraction of TBB 2.3.25-6, in about:config, it has that as user set ENABLED. But, I didn't enable it. The last thing I'd want to do if looking for speed, is use disk cache. Didn't touch the setting in Options nor reset it in about:config; used a clean profile. Others might check their setting in about:config. This is kind of a big deal for not retaining TBB sessions on the machine.

In my TBB about:config, browser.cache.memory.enable is also = true (by default). Only it has a much smaller max entry size than disk cache (which should be disabled): browser.cache.memory.max_entry_size;5120. So default memory max entry size is apparently 5.1 MB (kinda small if you have 8 or more GB RAM).

I don't know what TBB is REALLY doing when I go back one page in history, but unless that page has expired, been purged from cache, etc., it shouldn't be reloading it.

Maybe it has to do w/ how long I use TBB in a session - I only just opened it today. But today, going back a page or 2 in history is almost instant - as it should be. Yet I've seen the slow issue I've described over many versions. I hope it continues to make a liar out of me.

I'm not an expert on pipelining. TBB sets network.http.pipelining.maxrequests = 12, though most documentation says #s higher than 8 will be treated as 8.

Later TBB versions have network.http.pipelining.aggressive =true, while it's disabled by default in Fx 20. Some don't agree that it helps at all; in fact, just the opposite on some sites.
The biggest impact, however, was the variance. Using aggressive pipelining made certain sites MUCH slower. For example, about.com was 2.5 times slower <http://www.webpagetest.org/video/compare.php?tests=120725_BX_NF5-l:Pipelining+Off,120725_1J_NF4-l:Pipelining+On,120725_64_NF6-l:Aggressive+Pipelining> with aggressive pipelining. Other sites balanced this effect by being faster, with good results being 10-15% faster...

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