MySQL can use hashes as an index. It's an option on index creation. I suspect MySQLs indexing and caching system is multilayered and column type-specific. I'

MySQL can use hashes as an index. It's an option on index creation. I suspect MySQLs indexing and caching system is multilayered and column type-specific. I've written a couple of small DBs designed for domain-specific speedups, and I can say that one of the most difficult problems is cache integrity and data-state integrity, and I suspect why most databases are on the slow side is that they're designed first for data integrity and second for speed. memcached and similar aren't and I suspect that's one of the major reasons that it is much faster.