How MySQL Cluster Uses RAM

You may sometimes see that you have a RAM Alarm (CRITICAL or WARNING). 

If it is on the data node, it is generally nothing to worry about, but a SWAP alarm on the other hand is very severe.

The reason is that the data node statically allocates the RAM it will use, and never allocate more than that amount of RAM. Thus, if it uses 99% of the RAM, it will never use more. Currently we don't have a good way of really detecting if the data node is the alone  consumer of the e.g 99% RAM or if there may be another process consuming memory. Hence, we raise the ALARM to notify you about this.

You can check if you have other processes running on the data nodes that uses a lot of RAM, and in that case shut them down.

If you don't have any other major processes running on the server except the data node, then you can ignore the alarm you have got.

 More is coming here.