What is the proper way of Adding a Field in a MySQL table with 1.6 million row
ALTER on such a huge table can be slow irrespective of Engine_type

Follow this method to avoid downtime and quicker operation:


Setup slave
Stop replication.
Make ALTER on slave
Let slave catch up the master
swap master and slave, so slave becomes production server with changed structure and minimum downtime


You can also refer this post from MySQL Performance blog:

http://www.mysqlperformanceblog.com/2008/03/27/using-mmm-to-alter-huge-tables/