Hello,
I have been visiting some sites hosted on GAE and I found them to be very slow. Pretty much all of them take longer than usual to load.
Time: (in seconds) [ YSlow ]
9.9 giftag.com
3.1 hotskills.net
1.9 jeeyo.net
1.5 appspot.com
Is it that App Engine Cloud is too slow, Bigtable is too slow ... or what?
You're using the YSlow plugin to measure this, and YSlow tells you why the site is slow (the cunning name is the clue). For example, in the case of gifttag.com, YSlow reports that:
This page has 9 external Javascript scripts. Try combining them into one. This page has 3 external stylesheets. Try combining them into one. This page has 13 external background images. Try combining them with CSS sprites.
So it's get an 'E' grade for that. That's going to kill the perceived load performance of the site.
None of this has anything to do with appengine.
GAE's data access is in the order of seconds compared to a database which is measured in milliseconds. The difference is that BigTable scales to the millions of concurrent access due to the inherent isolation level of Read Uncommitted and the relaxed consistency.
No RDBMS can compute with that and still give consistency guarantees. To be honest, you don't really want to because for some applications you want strong guarantees over scalability.
YSlow has nothing to do with the speed of the web app on the server side since it's a completely client side speed measurement (css, javascript, browser rendering, image loading, etc). But on the other side, I have heard that your application may be slow on App Engine if doesn't have much hits and traffic. This makes the App Engine not to cache the python runtime environment (have cold start), so this can make significant difference in performance of applications with low traffic.