title: What the "16 MB of data limit" actually is of the `BatchWriteItem` API in DynamoDB?
body: <p>According to the doc:</p>
  <blockquote>
  <p>The BatchWriteItem operation puts or deletes multiple items in one or more tables. A single call to BatchWriteItem can write up to 16 MB of data, which can comprise as many as 25 put or delete requests. Individual items to be written can be as large as 400 KB.</p>
  </blockquote>
  <p>The definition is unclear, <code>16 MB of data</code> of what..?</p>
  <ol>
  <li>The whole HTTP request(header+body)?</li>
  <li>The total size of <a href="https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_BatchWriteItem.html#DDB-BatchWriteItem-request-RequestItems" rel="nofollow noreferrer">RequestItems.*</a> ?</li>
  <li>If 2 is true, is the size of <strong>marshall</strong> or <strong>unmarshall</strong> data? (Same question applies to <code>Individual items to be written can be as large as 400 KB</code> too)</li>
  </ol>
  <p>Does anyone know the details for this? I wasn't able to find any information on the docs.</p>