rpk cluster txn

The transactional ID is the string you define in clients when actually using transactions.

The producer ID is generated within clients when you transactionally produce.

The producer ID is a number that maps to your transactional ID, allowing requests to be smaller when producing, and allowing some optimizations within brokers when managing transactions.

Some clients expose the producer ID, allowing you to track the transactional ID that a producer ID maps to. If possible, it is recommended to monitor the producer ID used in your applications.

The producer epoch is a number that somewhat "counts" the number of times your transaction has been initialized or expired. If you have one client that uses a transactional ID, it may receive producer ID 3 epoch 0. Another client that uses that same transactional ID will receive producer ID 3 epoch 1. If the client starts a transaction but does not finish it in time, the cluster will internally bump the epoch to 2. The epoch allows the cluster to "fence" clients: if a client attempts to use a producer ID with an old epoch, the cluster will reject the client’s produce request as stale.

The state of a transaction indicates what is currently happening with a transaction. A high level overview of transactional states:

The last stable offset is the offset at which a transaction has begun and clients cannot consume past, if the client is configured to read only committed offsets. The last stable offset can be seen when describing active transactional producers by looking for the earliest transaction start offset per partition.