granularity of locking

what determines what level of locking(table level, page level or row level)
an object is locked in?
how do we determine from postgresql code what level a object is locked in?
Iam working on a project where i have to display the locks information of
all the transactions that have acquired locks in postgresql and i also have
to display that granularity(table level, page level, row level)on the locks
acquired by these transactions on objects.Which part of postgresql code
gives this information.?
thanks
Jenny

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