In a previous post, I had demonstrated how
subquery materialization, introduced in
MySQL 5.6.5, improves the performance of certain queries, like
query Q16 of DBT3. Such improvement was easily explained:
- Subquery materialization has a high start up cost (it needs to create and fill the temporary table).
- But afterwards it has fast lookups (temporary table has a hash index, no duplicates, and is in …