Joint Consensus #101
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Joint Consensus #101
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This was referenced Sep 12, 2018
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hicqu
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Jan 22, 2019
nolouch
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Jan 28, 2019
Signed-off-by: qupeng <qupeng@pingcap.com>
|
PTAL again pre-merge. Please pay particular attention to documentation. |
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This PR enables Joint Consensus as described by the Raft paper (https://raft.github.io/raft.pdf).
As of this commit it is possible to undergo arbitrary peer membership changes in a safe way.
Notably, this gives us a resilient "Replace Node" functionality, which is able to progress in the situation of a loss of both the old (removed) and new (added) peers go down. This is not possible with our previous one-at-a-time strategy.
Unfortunately, this feature is fairly large in scope. Thankfully it's mostly testing code!
There is some new API surface, notably the
Raft::begin_membership_changefunction.There is also some moved API surface. The
RaftLog::applied_tofunction has been moved toRaft::commit_apply. The old function, while it still works, carries a deprection warning. In the future we should make it a function available to onlyRaft::applied_to.Several APIs have changed to return errors instead of panic or otherwise ignore non-critical errors. In most cases you can just do
old_call().ok()to have the same behavior.Then, in order to facilitate the needs in testing, some additional API was added to the
Networkharness, which now can dispatch messages and not automatically send responses, allowing time to inspect the state of peers.Finally, many tests were added to ensure Joint Consensus can work.