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• A stream of committed operations that are guaranteed to be the same on all nodes in the replication group. Each operation in the stream is provided with a unique monotonous continuous index assigned by the replication module. The stream is durable and can be re-read as many times as needed as long as operations have not been compacted by a user/system request. The committed operations can be applied to the storage asynchronously as long as read operations are properly synchronized with the storage state to make sure to read-only when the needed operations are applied.
• A readIndex() operation that returns the most up-to-date committed (durable) operation index in the replication group providing linearizability. readIndex() performance varies from protocol to protocol: for canonical Raft, this operation involves a round-trip to the majority of group members from the current leader, while in PacificA primary node can return the index locally as long as the primary lease is valid. If a node has received and applied an operation with an index at least as large as the one returned by readIndex(), the state can be safely read locally.

Check the IEP-99: Pluggable replication page for details on a pluggable replication protocol.

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