MAXIMUM PATH LENGTH

Problem:
  Currently mysqld limits the max path char's to FN_REFLEN(512).
  When mysqld tries to create frm file or database directory
  it does not report error in case path is greater FN_REFLEN, but
  it does truncate the path to FN_REFLEN char and continue
  creating frm file or database directory with truncated name!!

Analysis:
  Mysql limits database_name/table_name identifier to max of
  64 characters. The frm file or directory are created
  using characters from identifiers itself, so it cannot exceed
  128+1(for /) characters. However, with UTF8 char in identifier
  we end-up creating frm file or directory name with 5 char per
  UTF8 char in identifier. This will be give us max of
  (64*5)+1(/)+(64*5) = 641 char, which is much higher
  than FN_REFLEN.

  We can consider increasing this limit FN_REFLEN, but the
  effort required to do that is more, and is not prefered now.

Fix:
  'CREATE TABLE', 'ALTER...RENAME', 'RENAME...TO' and
  'CREATE DATABASE' are only DDL's which can hit the limit.
  The current approach is the make sure these path give proper
  error to users. We check if path length to create 
  frm file or database directory hits the limit FN_REFLEN,
  if yes we throw a new error ER_PATH_TOO_LONG.