Digging into the code, throughputPerTask is being set by

Math.floor(configuredThroughput * throughputPercent)

where configuredThroughput is 40,000 by default if table is set to on-demand .

configuredThroughput can be set by String WRITE_THROUGHPUT = "dynamodb.throughput.write"

Seems the lower bound for write capacity is 4,000 units, so if you want to be very safe, set ddbConfWrite.set("dynamodb.throughput.write", "8000");

Refs: https://github.com/awslabs/emr-dynamodb-connector/blob/master/emr-dynamodb-hadoop/src/main/java/org/apache/hadoop/dynamodb/DynamoDBConstants.java

https://github.com/awslabs/emr-dynamodb-connector/blob/master/emr-dynamodb-hadoop/src/main/java/org/apache/hadoop/dynamodb/write/WriteIopsCalculator.java

https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/on-demand-capacity-mode.html