I really thought we were having a huge ammount of new visitors, but this is no longer a friendly wave of visitors and resembles a <a href="http://en.wikipedia.org/wiki/Denial-of-service_attack">DDoS</a> attack targeted to hog and overload the server.
Checking back the logs from the hosting company I've noticed that SQL usage has multiplied 5 times the regular usage since the 21st of June.
This excess of usage makes this site consume an exorbitant amount of bandwidth - luckily enough that we can endure this proportion of data transfer (and even bigger if necessary).
Unfortunately there isn't much to be done with the mySQL database which is taking most of the stress and was often giving the "error 500" messages when acessing the forums. I was hoping to place our database on other external servers where these requests could be balanced, but this is a bit dificult because I have no experience with this sort of handling - and it would be better not to risk the safety of our posts.
At the moment, I've removed all the extra "fluff" from the IPB forum software and disabled statistics displayed on the main page, search function, members viewing a forum, members who viewed a topic, similar topics, aniversary box were also disabled.
Reduced the counting of number of visitors to the last 5 minutes, also decreased the number of displayed topics on each category, removed gzip encoding while exchanging pages (more bandwith, but also less CPU overhead) and ensured that pages are cached on user's disk instead of always retrieving them from the server on multiple requests.
On the portal software, I've disabled the display of the last 1000 posts (will reduce google rank) and the left bar which was displayed while browsing the forum.
Some other internal improvements were also added to ensure the minimum SQL usage.
This removes much of the user friendly functions that keep everyone in touch with what is being discussed during the day but I hope to bring these addons back when we step over these server overload issues.
At least in the meanwhile we still have a working site instead of semi-offline one.
Peter has started a good post <a href="http://www.boot-land.net/forums/Error-500-t2482.html">here</a> to further comment this matter where everyone is welcome to write their comments or ideas.
Have a good weekend!
-- Nuno Brito