We recently had the case with one of our customers where we got externally generated random hash values (up to 70 bytes) and they were used as Primary Keys in InnoDB.
As we know, this is not a very good idea because the size of all secondary indexes becomes large and because a random hash value as a Primary Key gives us a bad locality of our rows in the table 1.
If we do not specify a Primary Key and have no Unique Key InnoDB generates a hidden Clustered Index based on the Row ID which is a 6 byte field. …
