<p>An identifier for the message in this batch.</p> <note> <p>The <code>Ids</code> of a batch request must be unique within a request. </p> <p>This identifier can have up to 80 characters. The following characters are accepted: alphanumeric characters, hyphens(-), and underscores (_). </p> </note>

<p>Set <code>MessageStructure</code> to <code>json</code> if you want to send a different message for each protocol. For example, using one publish action, you can send a short message to your SMS subscribers and a longer message to your email subscribers. If you set <code>MessageStructure</code> to <code>json</code>, the value of the <code>Message</code> parameter must: </p> <ul> <li> <p>be a syntactically valid JSON object; and</p> </li> <li> <p>contain at least a top-level JSON key of "default" with a value that is a string.</p> </li> </ul> <p>You can define other top-level keys that define the message you want to send to a specific transport protocol (e.g. http). </p>

<p>This parameter applies only to FIFO (first-in-first-out) topics.</p> <p>The token used for deduplication of messages within a 5-minute minimum deduplication interval. If a message with a particular <code>MessageDeduplicationId</code> is sent successfully, subsequent messages with the same <code>MessageDeduplicationId</code> are accepted successfully but aren't delivered.</p> <ul> <li> <p>Every message must have a unique <code>MessageDeduplicationId</code>.</p> <ul> <li> <p>You may provide a <code>MessageDeduplicationId</code> explicitly.</p> </li> <li> <p>If you aren't able to provide a <code>MessageDeduplicationId</code> and you enable <code>ContentBasedDeduplication</code> for your topic, Amazon SNS uses a SHA-256 hash to generate the <code>MessageDeduplicationId</code> using the body of the message (but not the attributes of the message).</p> </li> <li> <p>If you don't provide a <code>MessageDeduplicationId</code> and the topic doesn't have <code>ContentBasedDeduplication</code> set, the action fails with an error.</p> </li> <li> <p>If the topic has a <code>ContentBasedDeduplication</code> set, your <code>MessageDeduplicationId</code> overrides the generated one. </p> </li> </ul> </li> <li> <p>When <code>ContentBasedDeduplication</code> is in effect, messages with identical content sent within the deduplication interval are treated as duplicates and only one copy of the message is delivered.</p> </li> <li> <p>If you send one message with <code>ContentBasedDeduplication</code> enabled, and then another message with a <code>MessageDeduplicationId</code> that is the same as the one generated for the first <code>MessageDeduplicationId</code>, the two messages are treated as duplicates and only one copy of the message is delivered. </p> </li> </ul> <note> <p>The <code>MessageDeduplicationId</code> is available to the consumer of the message (this can be useful for troubleshooting delivery issues).</p> <p>If a message is sent successfully but the acknowledgement is lost and the message is resent with the same <code>MessageDeduplicationId</code> after the deduplication interval, Amazon SNS can't detect duplicate messages. </p> <p>Amazon SNS continues to keep track of the message deduplication ID even after the message is received and deleted. </p> </note> <p>The length of <code>MessageDeduplicationId</code> is 128 characters.</p> <p> <code>MessageDeduplicationId</code> can contain alphanumeric characters <code>(a-z, A-Z, 0-9)</code> and punctuation <code>(!"#$%&amp;'()*+,-./:;&lt;=&gt;?@[\]^_`{|}~)</code>.</p>

<p>This parameter applies only to FIFO (first-in-first-out) topics.</p> <p>The tag that specifies that a message belongs to a specific message group. Messages that belong to the same message group are processed in a FIFO manner (however, messages in different message groups might be processed out of order). To interleave multiple ordered streams within a single topic, use <code>MessageGroupId</code> values (for example, session data for multiple users). In this scenario, multiple consumers can process the topic, but the session data of each user is processed in a FIFO fashion. </p> <p>You must associate a non-empty <code>MessageGroupId</code> with a message. If you don't provide a <code>MessageGroupId</code>, the action fails. </p> <p>The length of <code>MessageGroupId</code> is 128 characters.</p> <p> <code>MessageGroupId</code> can contain alphanumeric characters <code>(a-z, A-Z, 0-9)</code> and punctuation <code>(!"#$%&amp;'()*+,-./:;&lt;=&gt;?@[\]^_`{|}~)</code>.</p> <important> <p> <code>MessageGroupId</code> is required for FIFO topics. You can't use it for standard topics. </p> </important>