orderingKey property

If non-empty, identifies related messages for which publish order should be respected.

If a Subscription has enable_message_ordering set to true, messages published with the same non-empty ordering_key value will be delivered to subscribers in the order in which they are received by the Pub/Sub system. All PubsubMessages published in a given PublishRequest must specify the same ordering_key value. For more information, see ordering messages.

Optional.