• scanning original relation R:   b_R
• writing partitions:   b_P   (b_R vs b_P ?)
• re-reading partitions:   b_P
• writing the result relation:   b_Out

To ensure that n is larger than the largest partition ...

• use hash functions (h1,h2) with uniform spread
• allocate at least sqrt(b_R)+1 buffers
• if insufficient buffers, significant re-reading overhead