partitionKey

Determines which shard in the stream the data record is assigned to. Partition keys are Unicode strings with a maximum length limit of 256 characters for each key. Amazon Kinesis Data Streams uses the partition key as input to a hash function that maps the partition key and associated data to a specific shard. Specifically, an MD5 hash function is used to map partition keys to 128-bit integer values and to map associated data records to shards. As a result of this hashing mechanism, all data records with the same partition key map to the same shard within the stream.

If the stream uses the USER_PARTITION_KEY record distribution strategy (the default), a partition key is required. If the stream uses the AUTO record distribution strategy, the partition key is optional and any value you provide is ignored, along with any ExplicitHashKey you provide. In that case, Amazon Kinesis Data Streams distributes the record across shards using service-managed algorithms. For more information, see UpdateStreamRecordDistributionStrategy.