Covering indexes can result in orders of magnitude performance improvements for queries. Bradley’s presentation on covering indexes describes what a covering index is, how it can effect performance, and why it works. However, the definition of a covering index can get cumbersome since MySQL limits the number of columns in a key to 16 (32 on MariaDB).
Tokutek introduced multiple clustering indexes into MySQL to address these problems. Zardosht describes the multiple clustering indexes feature and how clustering indexes differ from covering indexes. Zardosht[Read more...]