First, let’s discuss acknowledgement and deletion of messages in general. Quoting Concepts and Architecture / Messaging:

The consumer sends an acknowledgment request to the broker after it consumes a message successfully. Then, this consumed message will be permanently stored, and deleted only after all the subscriptions have acknowledged it. If you want to store the messages that have been acknowledged by a consumer, you need to configure the message retention policy.

You can control if message is retained, and for how long, using the retention policy:

• Message retention enables you to store messages that have been acknowledged by a consumer

Specifically, consumers of all active subscriptions.

Compaction by it self, as was written also honors retention, as written in Topic Compaction:

Topic compaction does, however, respect retention. If retention has removed a message from the message backlog of a topic, the message will also not be readable from the compacted topic ledger.

If you create a new subscription, and set it to read from EARLIEST message, and set Compacted Read to true, then it will read the data from the compacted topic up to the last message the compaction compacted, and from there it reads normally. If you want to keep the latest value for each key in-memory, the best is to use the TableView in the Client (are you using Java?)