LABjs messing up waterfall charts?

[aaronpeters]

Who would actually search for that in Google? My guess: # searches per month < 10

;-)

[sajal]

one thing... in most of the examples for the sequential loads... the dns is fired out sequentially... but the all those requests start downloading at around the same time... i.e. the green in the waterfall starts together.

[sajal]

Im seeing this sequential lookups more and more now.

See results for msn.com
IE7 : http://www.webpagetest.org/result/110308...02b4b320f/
IE8 : http://www.webpagetest.org/result/110308...c44bb2311/

Specifically this region


What are the odds of different servers finishing the initial connection portion at the exact same time?

These requests seems to be dynamically inserted scripts.

[aaronpeters]

Perhaps this is the case:
- IE initiates the requests for a bunch of files (here: 9)
- The first step is DNS lookup (here: 2 at a time)
- The second step is setting up the connection.
- The third step starts with the actual (GET) request going out, and IE wants to send out these requests all at the same time. In other words, the 'green' for object 1 needs to wait for the 'orange' of all other objects to finish.

This can't be true. Makes no sense.

[sajal]

Whatever the issue is... It seems IE9 fixed it. http://www.webpagetest.org/result/110308...6256e5942/

[pmeenan]

I don't know if I'd go as far as to say "fixed": http://www.webpagetest.org/result/110308...1/details/

   

Improved certainly, but not fixed. I'm pretty sure the problem is that something in IE is synchronizing to the main thread so you get a lot of these artificially extended network events. Catchpoint noticed it with other main-thread activities recently: http://blog.catchpoint.com/2011/03/02/newblindspot/ and it's something I've seen with javascript before as well. It MIGHT be possible for me to record the actual DNS and connect times and show gaps after them in the waterfall before the requests in these cases - need to look into it a bit more.

Certainly looks like some low-hanging fruit for the IE team to improve the browser performance though. I should have some experimental chrome support within the next week or so and it will be interesting to see how it compares.