Nodes are dying with OOM errors

Nodes are dying with OutOfMemory exceptions. Check for these typical causes:

Row cache is too large, or is caching large rows

Row cache is generally a high-end optimization. Try disabling it and see if the OOM problems continue.

The memtable sizes are too large for the amount of heap allocated to the JVM

You can expect N + 2 memtables resident in memory, where N is the number of tables. Adding another 1GB on top of that for Cassandra itself is a good estimate of total heap usage.

If none of these seem to apply to your situation, try loading the heap dump in MAT and see which class is consuming the bulk of the heap for clues.