Handling large traffic

[eluser]faceh[/eluser]
One of my sites is lucky enough to be receiving thousands and thousands of hits and orders a day, which is great! and generally Codeigniter is handling it all really well.

However looking at the server logs of slow mysql queries, adding to and cleaning the sessions table seems to be struggling a little. I changed this table to InnoDB hoping the single row locking would help, however this caused multiple issues with: "Deadlock found when trying to get lock; try restarting transaction" - which was a fatal error causing issues, so I've reverted back to MyISAM for now.

Does anyone have some tips on handling sessions with very high traffic levels?

Thanks.