Question 1
Consider a join (relation algebra) between relations r(R) and s(S) using the nested loop method. There are 3 buffers each of size equal to disk block size, out of which one buffer is reserved for intermediate results. Assuming size(r(R)) < size(s(S)), the join will have fewer number of disk block accesses if
relation r(R) is in the outer loop.
relation s(S) is in the outer loop.
join selection factor between r(R) and s(S) is more than 0.5.
join selection factor between r(R) and s(S) is less than 0.5.
       Database-Management-System       Joins       Gate 2014 Set -02
Question 1 Explanation: 
The join between r(R) and s(S) which is using nested loop will be as follows,
For each tuple r in R do
For each tuple s in S do
If r and s satisfy the join condition then
output the tuple
The above algorithm involves (nr*bs+br )
block transfer and (nr+br ) seeks.
br → no. of blocks in R
bs → no. of blocks in S
hr → no. of tuples in R
To have less block accesses in nr should be less and in question it is given that size(r(R)) < size(s(S)).
To have fewer no. of disk block accesses the relation r(R) should be in outer loop.
There is 1 question to complete.