I've got a bunch of mysql tables with the same structure and a hex md5hash unhexed stored as binary(16) in my mysql tables.<br/>However, when I add data randomly into my different mysql tables (to split write performance on different servers and tables), I can't enforce uniqueness without a centralized table with a UNIQUE/PRIMARY index or an external key-value optimized storage system.<br/>Mysql is TOO SLOW to enforce uniqueness because the time to insert decreases exponentially as you add more and more records to the unique table.<br/>I need a sample and working model with an external system like mongodb, couchdb, tokyocabinet, tokyotyrant, voldemort, or cassandra where before the md5hash is inserted into a mysql table, it is checked in batch against any of these systems.<br/>My requirements is that you can check and insert 1 Million unique hashes into the key-value store in under 5 seconds, when the key count in less than 100M unique keys, and the value are nulls.<br/>