Excessive RAM consumption in MySQL Cluster
The 429496 transaction records consume around 400 MBytes
(around 900 bytes per record).

The operation records consume also around 400 MBytes,
around 300 bytes in transaction coordinator and
500 bytes in ldm thread.

In addition it uses memory for a lot of other buffers such
as REDO buffers, SEND buffers, job buffers. These normally
consume a few hundred MBytes.

In addition you can decrease memory usage by setting
BatchSizePerLocalScan to a smaller value (e.g. 16).
This should save a few hundred MBytes of memory space.