Create an index on a huge MySQL production table without table locking

Question

I need to create an index on a ~5M rows MySQL table. It is a production table, and I fear a complete block of everything if I run a CREATE INDEX statement...

Is the

Answer 1

MySQL 5.6 update (feb 2013): You can now perform read and write operations while an index is being created even with InnoDB tables - http://dev.mysql.com/doc/refman/5.6/en/innodb-create-index-overview.html

In MySQL 5.6 and higher, the table remains available for read and write operations while the index is being created or dropped. The CREATE INDEX or DROP INDEX statement only finishes after all transactions that are accessing the table are completed, so that the initial state of the index reflects the most recent contents of the table. Previously, modifying the table while an index is being created or dropped typically resulted in a deadlock that cancelled the INSERT, UPDATE, or DELETE statement on the table.

and:

In MySQL 5.6, this feature becomes more general: you can read and write to tables while an index is being created, and many more kinds of ALTER TABLE operations can be performed without copying the table, without blocking DML operations, or both. Thus in MySQL 5.6 and higher, we typically refer to this set of features as online DDL rather than Fast Index Creation.

from http://dev.mysql.com/doc/refman/5.6/en/glossary.html#glos_fast_index_creation