Message ordering
Whether a queue delivers messages in the order they were sent; usually guaranteed only per key or partition, if at all.
Parallel consumers and retries reorder messages, so “updated” can arrive before “created”. Brokers such as Kafka keep order within one partition, so events for one order or one customer share a key and land in the same partition. Many queues give no order at all. A consumer can also carry a version number and ignore events older than what it has already stored.
Related terms
- At-least-once delivery: A queue or broker guarantee that every message arrives, possibly more than once, so consumers must handle duplicates.
- Aggregate (DDD): A cluster of objects changed as one unit, with a single root that enforces the business rules and marks the boundary of one transaction.
- Idempotency (idempotency key): An operation is idempotent if doing it twice has the same effect as doing it once. Retries become safe.
