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Effect of Buffer Management

Consider a query to find customers who are also employees: 

select c.name
from   Customer c, Employee e
where  c.ssn = e.ssn;

This might be implemented inside the DBMS via nested loops: 

for each tuple t1 in Customer {
    for each tuple t2 in Employee {
        if (t1.ssn == t2.ssn)
            append (t1.name) to result set
    }
}