\subsubsection{Nested Loops Join (NLJ)}
\begin{algorithm}
    \caption{Nested Loops Join Algorithm}
    \begin{algorithmic}[1]
        \Procedure{NestedLoopsJoin}{$R$, $S$}
            \For{each page $p_R \in R$}
                \For{each page $p_S \in S$}
                    \State Join the tuples on page $p_R$ with the tuples on page $p_S$ (evaluate the predicate for all pairs)
                    \State Add matching tuples to the join output
                \EndFor
            \EndFor
        \EndProcedure
    \end{algorithmic}
\end{algorithm}

The cost here is $P_R + P_R \cdot P_S$ I/Os, where $P_X$ is the number of pages in the relation $X$.
Furthermore, the DBMS should put the smaller relation on the outer loop to improve performance.