Dataypes: performance differences?

I'm new to pgsql. I just finished the basic design for my db and I am 
ready to start creating tables. In trying to decide which dataypes to 
use I would like to take into consideration performance and efficiency.

However I could not find any mention of the differences in performance 
amongst the various dataypes available. I am especially interested in 
the differences between the char/varchar/text datatypes and int2/int4.

Since I am new to this I am looking for documentation that would give me 
pointers as to when to use one datatype vs another and what the 
performance differences are.

If there is any online documentation can someone give me links to them?

Thanks!

Jc


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