Old thread but...
overhead is not really a problem it can be fixed by optimising it but your forum works now http://forums.firefusion.org/
It is a problem if you're running an unattended backup script as I am. The backup was stopping at 'online' because the table (presumably) had problems and the script includes a 'halt on an error' which also includes an email report function.
When I went in to repair the table via PhpAdmin, the only tool available was 'Flush'. No 'Repair' or 'Optimize'. That had me stumped for a while until I realised that the table type was 'HEAP'. Resetting it to 'MyISAM' gave me back the missing 'Repair' and 'Optimize' tools which I duly ran and the backup is now working fine again.
What confuses me is why this table was set to type 'HEAP'. The backup script I use does an online 'Check & repair' and it can't handle HEAP tables yet it's been running fine for about 2 months - so I only assume that the table type was reset somewhere between 2am on 24/05 and 2am on 25/05!
Any ideas as to how this could have happened? It's a tiny forum that's hardly used.