As per the documentation: If the content is updated on a regular basis, each forest should ideally have two CPUs (or cores) per forest. For example, a dual processor/dual core machine should be able to host two 256GB forests, and a quad processor/dual core system should be able to host four 256GB forests.
Does this mean that a forest can work with 1 core, but should ideally have two cores ? The statement and example tend to contradict each other.
To my knowledge this is more about competition for resources, than a strict requirement. You could probably host 10 forests even with just one core, but that would not help performance. More cores simply means more work can be done in parallel. 1 or 2 cores per forest is a good rule of thumb. If you have 2, one could work on querying, while the second is busy with updating. Then again, if you are only querying, 1 might be enough.
It is always good to monitor CPU load on peak load. You'd not want the system to idle a lot (over-capacity) unless you anticipate increase, but you don't want to overload either (maxing out at 100% a lot). CPU load of 50 to 75% sounds about right.
HTH!
The first line is a bit ambiguous. The first sentence appears to really make reference to threads, since that is how the examples are being measured. Since MarkLogic assumes intel chips, each core has 2 threads. So the recommendation really is 2 threads per forest.
So in the first example you have 2 cores at 2 threads each for 4 threads, to support 2 forests. The second has 4 cores at 2 threads each for 8 threads, to support 4 forests.
But as mentioned by Geert, you will want to take a look at performance. These recommendations don't take into account things like Anti-virus on the host system, heavyweight application or other things that could also consume cycles.
