Anonymous Flag with boost module enabled I have a node type which allow anonymous to use flag (Non global flag). 

The problem is with Boost enabled, all anonymous users have the same flag status at the cached page.

For eg, anonymous A Bookmarked a node and the page get cached, when anonymous B visited the page she has the Bookmarked status as well which is undesirable.

How should i update the flag status by user? 

Any suggestions are welcome!!
I'm not too sure, but you'd need to look into how Flag is handling the anonymous user session cookies. You may have to hack the code to add your own user-id and add it to the cookie...