Columns used in an index must be before any BLOB/TEXT columns. Currently the data column is 2nd; I propose to make the data column last so that the memory table could be used for the cache_* tables.
http://www.mysqlperformanceblog.com/2011/09/06/dynamic-row-format-for-me...
http://www.percona.com/doc/percona-server/5.5/flexibility/improved_memor...