I am not sure about the revision, but here are my create tables for session and messages, compare them with your table before applying any change of course. Also time your performances, for instance with firebug, before and after any change.

Cheers

CREATE TABLE `messages` (
`message_id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`user_id` int(10) unsigned NOT NULL DEFAULT ’0′,
`del` tinyint(1) NOT NULL DEFAULT ’0′,
`cache_key` char(32) CHARACTER SET ascii NOT NULL,
`created` datetime NOT NULL DEFAULT ’1000-01-01 00:00:00′,
`idx` int(11) unsigned NOT NULL DEFAULT ’0′,
`uid` int(11) unsigned NOT NULL DEFAULT ’0′,
`subject` varchar(255) NOT NULL,
`from` varchar(255) NOT NULL,
`to` varchar(255) NOT NULL,
`cc` varchar(255) NOT NULL,
`date` datetime NOT NULL DEFAULT ’1000-01-01 00:00:00′,
`size` int(11) unsigned NOT NULL DEFAULT ’0′,
`headers` text NOT NULL,
`structure` text,
PRIMARY KEY (`message_id`),
UNIQUE KEY `uniqueness` (`user_id`,`cache_key`,`uid`),
KEY `created_index` (`created`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=1093947 ;

CREATE TABLE `session` (
`sess_id` char(36) NOT NULL,
`created` datetime NOT NULL DEFAULT ’1000-01-01 00:00:00′,
`changed` datetime NOT NULL DEFAULT ’1000-01-01 00:00:00′,
`ip` char(16) NOT NULL,
`vars` text NOT NULL,
PRIMARY KEY (`sess_id`),
KEY `changed_index` (`changed`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

I know this post is a little bit old but I would like to know if it can improve the performance of Roundcube for me on version 0.7.2.

May I ask how can I know the maximum length of cache_key and data in my DB?
and also may I know the column you have changed in the session and messages table?

Thank you.

Andres

so thank you so much to share these very interesting discoveries.

best regards

tias