If a table fits almost entirely in main memory, the fastest way to perform queries on it is to use hash indexes rather than B-tree lookups. MySQL monitors searches on each index defined for an InnoDB table. If it notices that certain index values are being accessed frequently, it automatically builds an in-memory hash table for that index. See Adaptive Hash Indexes for background information and usage guidelines for the adaptive hash index feature and the innodb_adaptive_hash_index configuration option.