This page features every post I write, and is dedicated to Andrew Ho.
Link: https://dannyman.toldme.com/2011/09/11/911-ceremony-mountain-view-ca/
Tenth anniversary of the attacks. A bit difficult to recite the Pledge of Allegiance with that knot that still forms in the back of the throat.
Link: https://dannyman.toldme.com/2011/09/10/911-ceremony-in-mountain-view/
Civis Center Plaza, 11am
While diagnosing why an internal web site is slow for some users, I got data that our overseas colleagues see ping latency to the web site of around 200 ms. This is not unreasonable. Some web sites that attach a lot of additional objects cause remote clients to have to open several connections and make several round-trips to load and render a web page. What might work fine at 20 ms latency can really drag at 200 ms.
How to test this out? As a Linux user, I can use netem to induce added latency on my network interface:
# ping -qc 2 google.com PING google.com (74.125.224.145) 56(84) bytes of data. --- google.com ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 5009ms rtt min/avg/max/mdev = 4.136/4.197/4.258/0.061 ms # tc qdisc add dev wlan0 root netem delay 200ms # ping -qc 2 google.com PING google.com (74.125.224.144) 56(84) bytes of data. --- google.com ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 5474ms rtt min/avg/max/mdev = 205.006/205.034/205.062/0.028 ms # tc qdisc change dev wlan0 root netem delay 0ms # ping -qc 2 google.com PING google.com (74.125.224.50) 56(84) bytes of data. --- google.com ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 5011ms rtt min/avg/max/mdev = 4.117/4.182/4.248/0.092 ms
Note, I’m on wireless, so I’m tuning wlan0. you’ll want to hit eth0 or whatever is appropriate to your configuration.
The YSlow plugin or the Google Chrome Developer tool Network tab can be helpful to see what is going on:
Google Chrome's Developer Tool Network view without extra latency.
Google Chrome's Developer Tool Network view with extra 200ms latency.
So, with my web site, an added 200 ms latency doubles total page load time from 0.8 seconds to 1.6 seconds.
Here’s what I see when I visit the problem web site:
A problem web site at normal latency.
A problem web site at additional 200ms latency.
Total page load time at 7.5 seconds is nearly three times slower than without latency.
A very crude way to measure things is with wget on the command-line.
The wget man page mentions the -p (page requisites) option, then the author suggests wget -E -H -k -K -p <URL>. (You’ll need to RTFM yourself…) So I do:
$ cd /tmp $ sudo tc qdisc change dev wlan0 root netem delay 0ms $ time wget -q -E -H -k -K -p http://google.com real 0m0.160s user 0m0.010s sys 0m0.000s $ sudo tc qdisc change dev wlan0 root netem delay 200ms $ time wget -q -E -H -k -K -p http://google.com real 0m3.832s user 0m0.010s sys 0m0.000s
Of course, even with all those options, wget behaves very differently from a modern GUI web browser: there’s no caching, it doesn’t parse the DOM and it will blindly download requisites it doesn’t actually need. (Even a large font file found in a CSS comment.) And it does all its requests serially, whereas a modern GUI web browser will fetch several objects in parallel. And whatever web browser you use over a connection with induced latency is not going to replicate the experience of remote users pulling page requisites from zippy local CDNs.
At the end of the day, I proposed the following advice to my remote colleagues:
I also tweaked the web application to make it possible to show a more lightweight “dashboard” screen with fewer objects hanging off of it. This seems to improve load time on that page about 50%.
I am flying Virgin but this scene of silver-cylindered beauties struck my fancy.
There were a lot of these ladies at the park, and they were very busy.
Lake Point Tower rising majestically from the trees. Mei-Lin sais she thinks Oprah lives there, has four floors to herself. She doesn’t like to feel crowded, I guess.
My camera is dead so it is all about the Android phone now. This is Maggie, played with in PicSay Pro.
Weekends when the wife is not around I enjoy a visit to my favorite coffee shop. On this occasion while one patron was transcribing musical notation another regular started to work on the math of an idea about solar power generation.
Monday afternoon I biked down the Guadalupe trail past the airport to San Jose Diridon Caltrain and rode a comfy baby bullet home to Mountain View.
I have been writing most days at 750words.com. This is a little like Sy Safransky’s Notebook, as published in The Sun Magazine.
Maggie, content to sun on the porch, spares a moment to humor me by looking at the camera.
See also: Jessica Eats Breakfast
Link: https://dannyman.toldme.com/2011/08/27/we-dont-serve-pigeons-here/
It is probably just as well
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