Question

The MySQL documentation refers to the possibility of using a Hash Index in certain situations, see for example:

• http://dev.mysql.com/doc/refman/5.1/en/mysql-indexes.html
• http://dev.mysql.com/doc/refman/5.1/en/index-btree-hash.html
• http://dev.mysql.com/doc/refman/5.1/en/innodb-adaptive-hash.html

That is, the Hash Index is supported on a MEMORY table (and NDB; see also MySQL Static Hash-index), and that InnoDB can adaptively use a Hash Index if beneficial.

However, the above documentation is a bit sparse. Is there any other good documentation/reference for the particular uses/details of Hash Index in MySQL? The basic hashing behavior is implied, but some more particulars would be nice.

Answer 1

You can read this :

• http://jameshalsall.co.uk/emulating-mysql-hash-indexes-on-myisam-tables/