/etc/init/mysql.override:

# Raise open files limit # Ref: http://serverfault.com/questions/440878/changing-open-files-limit-in-mysql-5-5 limit nofile 32000 32000 limit nproc 32000 32000

Stop server. Make a full binary backup of datadir.
Follow http://dev.mysql.com/doc/refman/5.6/en/innodb-troubleshooting.htmlRead more... )

Let's assume we have a table of the following structure:
CREATE TABLE `xxx` ( `xxx` varchar(250) CHARACTER SET latin1 COLLATE latin1_swedish_ci DEFAULT NULL, `yyy` varchar(250) CHARACTER SET cp1251 COLLATE cp1251_general_ci DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=latin1" populated with some data
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