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Merge pull request #2553 from xiang90/raft-design

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raft: add progress state machine graph
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Xiang Li 2015-03-20 19:57:51 -07:00
commit 09a86cb9b9
1 changed files with 29 additions and 0 deletions
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raft/design.md
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@ -8,6 +8,35 @@ A progress has two attribute: `match` and `next`. `match` is the index of the hi
A progress is in one of the three state: `probe`, `replicate`, `snapshot`.
```
+--------------------------------------------------------+
| send snapshot |
| |
+---------+----------+ +----------v---------+
+---> probe | | snapshot |
| | max inflight = 1 <----------------------------------+ max inflight = 0 |
| +---------+----------+ +--------------------+
| | 1. snapshot success
| | (next=snapshot.index + 1)
| | 2. snapshot failure
| | (no change)
| | 3. receives msgAppResp(rej=false&&index>lastsnap.index)
| | (match=m.index,next=match+1)
receives msgAppResp(rej=true)
(next=match+1)| |
| |
| |
| | receives msgAppResp(rej=false&&index>match)
| | (match=m.index,next=match+1)
| |
| |
| |
| +---------v----------+
| | replicate |
+---+ max inflight = n |
+--------------------+
```
When in `probe` state, leader sends at most one `replication message` per heartbeat interval. The leader sends `replication message` slowly and probing the actual progress of the follower. A `msgHeartbeatResp` or a `msgAppResp` with reject might trigger the sending of the next `replication message`.
When in `replicate` state, leader sends `replication message`, then optimistically increases `next` to the latest entry sent. This is an optimized state for fast replicating log entries to the follower.