How can I speed up "show columns" on MySQL?
MySQL recalculates table statistics for certain operations that access INFORMATION_SCHEMA tables (SHOW COLUMNS is just a convenient alias for querying INFORMATION_SCHEMA.COLUMNS).  Set innodb_stats_on_metadata to be false, which will prevent this recalculation from occurring when you ask for metadata from the table. 

SET GLOBAL innodb_stats_on_metadata=0;


and add the following to my.cnf

[mysqld]
innodb_stats_on_metadata = 0