I posted about this a while back, but never found the reason for it.
http://groups.google.com/group/firebug/browse_thread/thread/33d1739064de61d5?tvc=2&pli=1
http://code.google.com/p/fbug/issues/detail?id=3809
To me, it seems like it's a bug in Firefox or Firebug as the time is
blocking time not DNS time.
A funny thing is that when we switched from Apache to using Varnish to
serve those files, the "problem" went away.
Adrian
On 04/28/11 14:36, RichardLynch wrote:
The message I sent to Marketing:
It took me a few reads to get it, but here's a loose translation:
1) Compose an HTTP request to get the asset. (Chump change time)
2) Resolve the DNS name to an IP address (or not, if it IS an IP)
3) Wait for an open "slot" in the 4 (by default) that Firefox
allocates for any given domain name (depends on previous resource load
times)
4) Send the request and start waiting to connect (which is GREEN BAR
time)
If you look carefully at the blue bars, you will see that each BLUE
BAR right-hand ending corresponds to an earlier request full bar
ending.
In other words, if you have FIVE requests in a row to the same server,
you might see this:
1) brownnnnnpurplllle
2) brownpurple
3) brownnnnnnnnnnnnpurplllllllle
4) brownnnnnnnnnpurplllllllle
5) BLUEBLUEBLUbrownpurple
The BLUEBLUE part is *WAITING* for one of the first four to finish,
because Firefox only opens four channels at once to any given server.
So when 2) finished, 5) gets to "start" and the BLUE changes to brown.
Any BLUE bits you see could contain some element of "DNS Lookup", but
more likely is waiting for an open channel.
More images, more BLUE, more waiting.
This is why some sites have images.example.com or even
images1.example.com and images2.example.com
Each sub-domain gives more "channels" to Firefox, in theory.
In practice more than a couple extra extra sub-domains kills the
browser cache, and ends up hurting more than it helps.
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