The OOM message shows that Apache get it.....
"apache2 invoked oom-killer"
This happened before I doubled the RAM - and I also use caches for the wordpress and flush RAM once in a while. In other words, I never see the system eating up available memory - the error seems to come out of nowhere....
Looking around the web, I saw some folks mention that it could be a fault of Linux stock settings - that they are not overcommitting:
Anyone else have experience with this syndrome? It seems that if it were default behavior in Linux, it would be happening to lots of people!