raft,tracker: track follower commit index #132
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This PR closes a gap in commit index tracking, and reduces the number of unnecessary
MsgApp
messages in the system.Previously, the leader did not precisely know what commit index the follower is at, and always had to send an empty
MsgApp
to bring it up to date if it's not.With this change, followers now send the commit index of their logs back to the leader, and the leader tracks each follower's commit index. This allows the leader to send an empty
MsgApp
with a commit index update only if the tracked index is behind.Resolves #131