Extjs 3 to Extjs 4 [closed]

Question

I want to migrate from extjs 3 to extjs 4. I have tested sample Extjs 4 example in rails 3. I have observed that page rendering time is very slow in extjs 4. I don't know what is the reason.
Can anybody tell me, what is the reason behind that? or
is there any problem in my app? and
What should I do to improve the perfomance of extjs 4?

Answer 1

ExtJS 4.0 has performance issues,

ExtJS 4.0.2 is the release you need that fixes most performance issues, it is still slow though...

Google for ExtJS 4 performance