Recently we have migrated some of less intensive sites to weaker servers, and noticed quite strange behavior: mysql starts consuming more and more memory till it crashes. The loads go up as all the memory and swap space is consumed. We could not track down the problem easily. We tried to find out what’s the problem for a couple of days till we found out.
We used third party software – a skinned phpbb to enhance the site. This is a well known forum solution, and we decided using it although we already had some problems. And it looks like it does work well with mysql5 (or at least all versions till 2.0.18 does not). The problem occurs in search module of the phpbb and you can either try to upgrade the software or disable searching.
Generally, I do not suggest using phpbb for the sites. Two of the sites had been hacked in because we failed to update phpbb in time, and vulnerabilities are discovered often. It’s better to look for other board solutions.