Consider joining R with S above.

In each table, the first column is rids and the second column is the join

column. Assume that a disk page holds $2$ records and the memory B has $4$

pages.

$(1)$ What is the IO cost of sort$-$merge join of R and S$.$ You need to

consider all options of outer and inner during merging. Explain the

cost

You can ignore the IO cost of writing the join result. Do not use $3(|$R$|+|$S$|).$