Help in Postgresql

[mooh Rash]

Hi ,
I am a PhD student searching in query optimization. I want to access the 
information about queries and statistics. Especially, I am interested in   
finding out how I can collect the history information (user, when, query, 
query_plan) from postgreqsl. Also, I wonder if there is a plan-table in 
postgresql than I can access, and I can access it?. I appreciate if you guide 
me in getting the mentioned information that are necessary for my research.
Best,Moohanad