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 # xraft
 
-my raft implementation
+A raft implementation of XnnYygn's.
 
-* xraft-core
-* xraft-kvstore
+I want to make something with netty framework, and I found raft. Raft is interesting. As the first distributed consensus algorithm I learnt, I read the paper and implemented almost all of the feature of raft including
+
+* Leader election and log replication
+* Membership change(one server change)
+* Log compaction
+
+All these feature are implemented in xraft-core. And the client interaction in raft, I thought, should be the feature of service based on xraft-core. Until now, I made a simple key value store based on xraft-core, called xraft-kvstore. It supports GET and SET command.
+
+## Demostration
+
+To test xraft with xraft-kvstore, you can download xraft and run xraft-kvstore, xraft-kvstore-cli.
+
+### Prerequistes
+
+Java 1.8+ is required to run xraft. You can run `java -version` to check the version of java on your computer.
+
+### Download
+
+You can get complied xraft in releases.
+
+### Run Server
+
+`xraft-kvstore` under the `bin` directory is the command to run xraft kvstore server.
+
+To demostrate a xraft cluster with 3 nodes(memory log mode), 
+
+* node A, host localhost, port raft node 2333, port kvstore 3333
+* node B, host localhost, port raft node 2334, port kvstore 3334
+* node C, host localhost, port raft node 2335, port kvstore 3335
+
+start servers with commands below
+
+Terminal A
+
+```
+$ bin/xraft-kvstore -gc A,localhost,2333 B,localhost,2334 C,localhost,2335 -m group-member -i A -p2 3333
+```
+
+Terminal B
+
+```
+bin/xraft-kvstore -gc A,localhost,2333 B,localhost,2334 C,localhost,2335 -m group-member -i B -p2 3334
+```
+
+Terminal C
+
+```
+bin/xraft-kvstore -gc A,localhost,2333 B,localhost,2334 C,localhost,2335 -m group-member -i C -p2 3335
+```
+
+Since the minimum election timeout is 3 seconds, if you cannot execute all 3 commands within 3 seconds, you will get some error like `failed to connect ....`. But after you started all nodes, the error will disapper.
+
+After start, you will see something like `become leader`, `current leader is xxx` and it shows the cluster is started and leader election is ok.
+
+### Run Client
+
+Run `xraft-kvstore-cli` with the cluster configuration. The client will not connect to any node in cluster so it is ok to run client before cluster starts.
+
+```
+$ bin/xraft-kvstore-cli -gc A,localhost,3333 B,localhost,3334 C,localhost,3335
+```
+
+It will run an interative console, press TAB two times and you will get the available commands. For this demostration, firstly run 
+
+```
+kvstore-get x
+```
+
+and you should get the result `null`. Then run
+
+```
+kvstore-set x 1
+```
+
+nothing will be printed, now you can run get again.
+
+```
+kvstore-get x
+```
+
+`1` should be printed.
+
+## New Service
+
+How to create new service based on xraft-core?
+
+### Create Node
+
+The core component of xraft is the interface `Node`, new service should create the instance of node by `NodeBuilder`.
+
+The simplest pattern, standalone, memory log
+
+```
+Node node = new NodeBuilder(new NodeEndpoint("A", "localhost", 2333)).build();
+```
+
+Cluster, file log
+
+```
+Node node = new NodeBuilder(
+  Arrays.as(
+    new NodeEndpoint("A", "localhost", 2333),
+    new NodeEndpoint("B", "localhost", 2334),
+    new NodeEndpoint("C", "localhost", 2335)
+  ))
+  .setDataDir("/path/to/data/dir")
+  .build();
+```
+
+### Use Node
+
+API
+
+* registerStateMachine(StateMachine)
+* start()
+* getRoleNameAndLeaderId()
+* addNodeRoleListener(NodeRoleListener)
+* appendLog(byte[])
+* addNode(NodeEndpoint)
+* removeNode(NodeId)
+* stop()
+
+A service should register its statemachine by `registerStateMachine` before appending any log.
+
+`start` and `stop` should be called when service starts or stops.
+
+To check current node is leader you can call `getRoleNameAndLeaderId` or add a listener.
+
+`addNode` and `removeNode` is the api for membership change.
+
+BTW, `Node` is thread safe.
+
+### StateMachine
+
+In xraft, it's the service's responibility to manage statemachine, including `lastApplied`. xraft-core provides two abstract implementation of statemachine
+
+* AbstractDirectStateMachine
+* AbstractSingleThreadStateMachine
+
+The first one will apply the log in node's thread, and the second one will apply log in its thread, in another word, asynchronously. 
+
+### Snapshot
+
+In other's implementation of raft, there's some configuration of something like when to generate snapshot. But as a general purpose raft implementation, it's service who called `StateMachineContext#generateSnapshot` to tell xraft-core to generate snapshot. 
+
+Currently, generating snapshot will block other operations, I will try to fix this problem.
+
+For more detailed implementation of new service, see the source code of xraft-kvstore.
+
+## Build
+
+xraft use `Maven` as build system.
+
+```
+$ mvn clean compile install
+```
+
+To package xraft-kvstore
+
+```
+$ cd xraft-kvstore
+$ mvn package assembly:single
+```
+
+## License
+
+This project is licensed under the MIT License.
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