title: DynamoDb Batch write update
body: <p>When we do <code>table.batch_writer()</code> , the boto3 API , does it insert or it updates as well?</p>
  
  <p>By Update i mean the <code>partition key</code>, <code>sort key are same</code> , but other <code>attributes</code> are not same.I cannot find this in any documentation.</p>