MySQL Cluster supports storing non-indexed columns on disk-only with an LRU cache of recently accessed data. However indexed columns are always held in-memory.

MySQL Cluster preallocates all memory, according to the DataMemory and IndexMemory parameters. It will not ask the underlying OS for more memory dynamically.

This means that you need to have configured enough memory across your cluster to hold all indexed columns in memory. If your dataset is large enough that the indexed columns are larger than the available cluster memory, then you cannot load that dataset into the cluster. At some point you will run out of space, and your inserting transactions will be aborted.

When configuring DataMemory and IndexMemory, it is best to limit yourself to somewhat less than the physical memory in each system. Some physical memory should be reserved for the OS and other processes.

Theoretically MySQL Cluster can be configured so that it uses virtual memory via a swap device (e.g. more than physical memory), but as the other answers state, this is not a designed-for use case. Having in-memory structures swapped to disk is usually sub-optimal as in-memory random access patterns result in random access to the disk, resulting in swap thrashing and slowdown across the system. With MySQL Cluster, the most likely outcome is heartbeat failure and cluster failure due to a swapping data node not responding to signals quickly enough.

To efficiently support larger-than-aggregate-memory indexes, MySQL Cluster would need to support on-disk index formats (perhaps a B tree etc) with caching and access patterns aligned with disk access properties.

DISCLAIMER : Not SCMCDBA Certified

If you plan to hold data in memory, you need to

• increase RAM on all data nodes to 16GB
• increase the DataMemory to 6GB
• increase the number of SQL nodes to 3 (Makes SQLNodes to DataNodes 1:1)

If you cannot make these changes, then you should offload data to local storage

• MySQL Cluster -- Storing table data on data nodes

Here is one of the best answers from Frazer Clement : MySQL Cluster RAM requirement

He states in his answer

When configuring DataMemory and IndexMemory, it is best to limit yourself to somewhat less than the physical memory in each system. Some physical memory should be reserved for the OS and other processes.

There are three MySQL Cluster Gurus in this forum

• Frazer Clement
• Mat Keep
• Andrew Morgan

Checks out their answers !!!