Question: I'm using JasperReporting engine, and i need to optimize reporting performance. Currently my application compiles reports from \*.jrxml files every time, as I'm not changing the reports now and app is not able to generate user-defined reports I should compile them once and use .jasper files in future..... AM I RIGHT?? And do I need to re-compile them?
Thanks in advance!

Answer: 
AutoPostBack set to true will initiate a page postback (like clicking a button) whenever a server event for the control is fired. Server-side code tied to initiated control events will happen immediately (along with a full/partial page load).

AutoPostBack set to false will NOT initiate this and event code will not fire until another "posting-back" event fires.
A simple google would have told you the answer to this:

Robbed from here as I thought someone else would be able to explain this better than me.

<http://www.asp101.com/samples/autopostback_aspx.asp>

> 
> AutoPostBack is built into the
>  form-based server controls, and when
>  enabled, automatically posts the page
>  back to the server whenever the value
>  of the control in question is changed.
>  Because of the additional server
>  requests it causes, it's not something
>  you'll want to enable for all your
>  controls, but for things that affect
>  page display or change choices further
>  down the form, it can be really handy.
>  Not to mention the fact that it will
>  save you a lot of time and headaches
>  over trying to implement something
>  similar on your own. Not that it's
>  really all that complex to do on your
>  own if you're good with javascript,
>  but it's hard to get any simpler then
>  just setting AutoPostBack="True"
> 
> 
> 

One thing to point out, this will only work when javascript is enabled, in the absense of javascript you will need to provide another mechanism to envoke the postback.