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Overview

This lecture will cover join algorithms, focusing in particular on Hash join and Sort-Merge join and the relative tradeoffs of the two approaches.

Read the following paper:

• Shapiro, L. D. "Join Processing in Database Systems with Large Main Memories." In Readings in Database Systems. San Fransisco, CA: Morgan Kaufmann, 1998. ISBN: 1558605231.

As you read, think about and come to class prepared to answer the following questions:

• Under what circumstances is Sort-Merge join preferable to hash?
• Both Hash join and Sort Merge join on unsorted inputs perform approximately the same number of I/Os. So why does one sometimes outperform the other?
• Under what circumstances would index-nested loops join be preferable to hash or sort-merge join?