1. Latency Kills
Optimize your apps for latency
Shishir Birmiwal
Software Engineer
Google Confidential and Proprietary 1

2. Is latency that bad?
Why all the fuss?
Lets take a pop quiz!
Google Confidential and Proprietary 2

3. Question# 1
Have you closed a page
because it didn't load up in time?
Google Confidential and Proprietary

4. Question# 2
Have you re-clicked links?
Google Confidential and Proprietary

5. Question# 3
How would you feel if you have to wait 15
seconds between views?
Google Confidential and Proprietary

6. Latency Kills
• Amazon reported that 100ms of latency costs sales by 1%
• An additional 500ms latency saw Google search usage drop by 20%
• Users perceive Quality and Ease of Use with lower latency
Google Confidential and Proprietary

7. Sources of latency
Why do we have latency?
Google Confidential and Proprietary 7

8. Sources of latency
fetch page
gadget xml
fetch gadget iframe
fetch social data
Client fetch backend data Container Application
Browser (orkut) backend data Backend
content render
Google Confidential and Proprietary

9. Kill latency
Optimize your app
Google Confidential and Proprietary 9

10. Optimize your app
• Batch requests
• Caches are your friends
• Minify static content
• Be lean and mean
• Think ahead
• Best practices
Google Confidential and Proprietary

11. Optimize your app
Batch Requests
Put multiple independent requests together
var idspec = opensocial.newIdSpec({ quot;userIdquot; : quot;OWNERquot;, quot;groupIdquot; : quot;FRIENDSquot; });
var fields = [ quot;AppField1quot;, quot;AppField2quot;, quot;AppField3quot; ];
var req = opensocial.newDataRequest();
req.add(req.newFetchPersonRequest(opensocial.IdSpec.PersonId.OWNER), quot;get_ownerquot;);
req.add(req.newFetchPeopleRequest(idspec), quot;get_friendsquot;);
req.add(req.newFetchPersonAppDataRequest(idSpec, fields), quot;owner_dataquot;);
req.send(response);
Google Confidential and Proprietary

12. Caches are your friends
Proxy Content
Use gadgets.io.getProxyUrl(url) to get a proxy URL
var imgUrl = gadgets.io.getProxyUrl('http://example.org/image.png');
var html = '<img src=”' + imgUrl + '”>';
Content-rewrite
Automatically rewrite URLs to fetch from cache
<Optional feature=”content-rewrite”>
<Param name=”include-urls”>.*</Param>
<Param name=”exclude-urls”></Param>
<Param name=”include-tags”>img,script,embed,link,style</Param>
</Optional>
http://www.example.org/image.png becomes something like:
http://www1.orkut.gmodules.com/gadgets/proxy?url=http://example.org/image.png
Google Confidential and Proprietary

13. Caches are your friends
Use cache effectively
• makeRequests are cached; specify refresh interval
• set HTTP cache-headers effectively
BYO cache
• store user specific data in app data – faster to access
• cache global info in app data
 e.g. high scores
 update content in app data from backend as required
Google Confidential and Proprietary

14. Optimize your apps
Minify static content
• re-compress images to smaller sizes
• serve smaller and gzipped JS/CSS files
• concat. JS/CSS files to reduce number of fetches
• include JS/CSS in gadget XML if possible
Google Confidential and Proprietary

15. Optimize your apps
Be lean and mean
lighter faster profile pages
• use images, not swfs
• use app data as cache
• use owner/viewer only signed makeRequest
• may choose to show owner-only data on profile pages
• don't load unnecessary files
Google Confidential and Proprietary

16. Think ahead
• Expect user requests and prefetch content
• Preload content from your servers
<ModulePrefs ...>
...
<Preload href=”http://example.com/topScores”>
</ModulePrefs>
or
<Preload href=”http://example.com/myScores” authz=signed views=”profile,canvas”
signViewer=false>
Google Confidential and Proprietary

17. Best practices
• Show a “loading gif” image when expecting the user to wait
• Put Stylesheets at top
• Put Scripts at bottom
• Post-load components
• Use Google's cached version of JS libraries
Google Confidential and Proprietary

18. Demo time
Firefox extensions are your friends!
• Firebug
• Live HTTP Headers
• YSlow
Google Confidential and Proprietary

19. Thank You!
Optimize your app and save the day!
Google Confidential and Proprietary 19