Support checking assertion of Leadership #1
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This allows clients of this library to check if the current node, assuming it is the Leader, has explicitly asserted leadership in the current term. "Asserting" is defined has having committed at least one log entry in the current term, as per the Raft paper. This change adds a new channel, which is only serviced when in Leadership mode. This channel will respond with the asserted status via a Future. Clients are recommended to call this function only until they have confirmed that the leadership has been asserted. Once asserted for a given term the state can be cached until the end of the term. This code is necessary to properly implement the Read Optimization outlined in the Raft paper and dissertation. The dissertation explains that it is not sufficient to simply check the Leader's commit index. Instead a client must first confirm that the Leader has explicitly asserted leadership by committing a log entry in the current term. Only then is commit index valid.
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This allows clients of this library to check if the current node, assuming it is the Leader, has explicitly asserted leadership in the current term. "Asserting" is defined has having committed at least one log entry in the current term, as per the Raft paper.
This change adds a new channel, which is only serviced when in Leadership mode. This channel will respond with the asserted status via a Future. Clients are recommended to call this function only until they have confirmed that the leadership has been asserted. Once asserted for a given term the state can be cached until the end of the term.
This code is necessary to properly implement the Read Optimization outlined in the Raft paper and dissertation. The dissertation explains that it is not sufficient to simply check the Leader's commit index. Instead a client must first confirm that the Leader has explicitly asserted leadership by committing a log entry in the current term. Only then is commit index valid.