LONGTEXT [CHARACTER SET charset_name] [COLLATE collation_name]

A TEXT column with a maximum length of 4,294,967,295 or 4GB (232 − 1)
characters. The effective maximum length is less if the value contains
multibyte characters. The effective maximum length of LONGTEXT columns
also depends on the configured maximum packet size in the client/server
protocol and available memory. Each LONGTEXT value is stored using a
4-byte length prefix that indicates the number of bytes in the value.

URL: http://dev.mysql.com/doc/refman/5.6/en/string-type-overview.html

