Data too long for column for longtext datatype - MySqlException
http://dev.mysql.com/doc/refman/5.7/en/string-type-overview.html


  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.




http://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_max_allowed_packet
http://dev.mysql.com/doc/refman/5.7/en/memory-use.html