privilages system table in postgres Is it possible to know all the tables a user has access to using a single query?

I tried with pg_role and pg_user with no luck. Can anyone tell me about a system table which has the data of all the objects that a user has access to?
I don't think there is a canned view for that purpose, but such a query is possible to write.

You'd have to query each object type independently, forming a big UNION. A number of system information functions are available for checking permissions on objects, see the Access Privilege Inquiry Functions table.

Combine them with queries over information_schema, or over the internal PostgreSQL tables like pg_class, pg_proc, etc, and you'll be able to collect the desired information.

You might find the queries psql uses to implement \dp and the various + commands like \df+ informative. Run psql with -E to see them.