In-Memory Data Store multi-sharding - controller dies when a large data set pushed into the data store

In the IMDS multi-sharding setup, the controller dies when a large data set is pushed into the data store. For example, pushing 1 million entries (a list of strings) into a single shard kills the controller. Pushing 500k entries per-shard into two shards kills the controller. But, pushing 250k entries per-shard into 4 shards works. By "kills the controller" i mean the CPU util goes to 100% and the controller stops responding.

To reproduce:
1. build coretutorials/clustering/shardingsimple in master
2. Start the controller build in Step 1 (./karaf/target/assembly/bin/karaf)
3. Point the browser to the controller (e.g. http://localhost:8181/index.html)
4. Go to Yangman on the selection menu on the left
5. Select the shardingsimple -> operations model
6. Enter the following JSON for "sent data:
{
"shard-test": {
"input":

{ "test-type": "ROUND-ROBIN", "data-store": "CONFIG", "shards": "2", "dataItems": "500000", "putsPerTx": "1", "listeners": "1", "precreate-data": "true", "validate-data": "false" }

}
}