zk 两阶段提交(待完善)
zk 节点是一个 QuorumPeer,选举结束后,leader 和 follower 各自执行自己的逻辑:
org.apache.zookeeper.server.quorum.QuorumPeer#run org.apache.zookeeper.server.quorum.QuorumPeer#setLeader
org.apache.zookeeper.server.quorum.Leader#lead org.apache.zookeeper.server.quorum.QuorumPeer#setFollower
org.apache.zookeeper.server.quorum.Follower#followLeader
不管是 leader 还是 follower,都封装了一个 QuorumPeer 对象,QuorumPeer.ServerCnxnFactory 监听端口,处理客户端 io 事件。
请求处理的入口:把请求交给 procesor 链的 firstProcessor
org.apache.zookeeper.server.ZooKeeperServer#processPacket
leader
构建 processor 链
// org.apache.zookeeper.server.quorum.LeaderZooKeeperServer#setupRequestProcessors
protected void setupRequestProcessors() {
RequestProcessor finalProcessor = new FinalRequestProcessor(this);
RequestProcessor toBeAppliedProcessor = new Leader.ToBeAppliedRequestProcessor(
finalProcessor, getLeader().toBeApplied);
commitProcessor = new CommitProcessor(toBeAppliedProcessor,
Long.toString(getServerId()), false,
getZooKeeperServerListener());
commitProcessor.start();
ProposalRequestProcessor proposalProcessor = new ProposalRequestProcessor(this,
commitProcessor);
proposalProcessor.initialize();
firstProcessor = new PrepRequestProcessor(this, proposalProcessor);
((PrepRequestProcessor)firstProcessor).start();
}
请求处理链:PrepRequestProcessor, ProposalRequestProcessor, CommitProcessor, ToBeAppliedRequestProcessor, FinalRequestProcessor
由 ProposalRequestProcessor 构造函数可,还有一条链:SyncRequestProcessor, AckRequestProcessor
public ProposalRequestProcessor(LeaderZooKeeperServer zks,
RequestProcessor nextProcessor) {
this.zks = zks;
this.nextProcessor = nextProcessor;
AckRequestProcessor ackProcessor = new AckRequestProcessor(zks.getLeader());
syncProcessor = new SyncRequestProcessor(zks, ackProcessor);
}
follower
构建 processor 链
org.apache.zookeeper.server.quorum.FollowerZooKeeperServer#setupRequestProcessors
链1:FollowerRequestProcessor, CommitProcessor, FinalRequestProcessor
链2:SyncRequestProcessor, SendAckRequestProcessor
两阶段写
leader 接收写请求,反序列化请求体
org.apache.zookeeper.server.PrepRequestProcessor#processRequest
leader 发送建议给 follower
// org.apache.zookeeper.server.quorum.ProposalRequestProcessor#processRequest
zks.getLeader().propose(request);
leader 发送建议给自身
// 由 leader 的 SyncRequestProcessor 把请求写入事务日志
syncProcessor.processRequest(request);
leader 的 AckRequestProcessor 返回 ack 给自身
org.apache.zookeeper.server.quorum.AckRequestProcessor#processRequest
follower 接收并处理 leader 发送的建议
org.apache.zookeeper.server.quorum.Follower#processPacket
follower 的 SyncRequestProcessor 写入事务日志
org.apache.zookeeper.server.SyncRequestProcessor#run
follower 的 SendAckRequestProcessor 发送 ACK 给 leader
org.apache.zookeeper.server.quorum.SendAckRequestProcessor#processRequest
leader 接收并处理 follower 的 ack
org.apache.zookeeper.server.quorum.LearnerHandler#run
org.apache.zookeeper.server.quorum.Leader#processAck
ack 超过半数,向 follower 发送提交事件(把数据放入发送队列),并把写操作应用到 DataTree
follower 提交写操作,把数据写入 DataTree
CommitProcessor 和 FinalRequestProcessor
数据写入的 2 个关键时机
写事务日志
// org.apache.zookeeper.server.SyncRequestProcessor
zks.getZKDatabase().append(si)
写 DataTree
// org.apache.zookeeper.server.FinalRequestProcessor
getZKDatabase().processTxn(hdr, txn)
异常情况一:follower 处理 propose 超时,leader 如何处理?
leader 定期发送 ping 给 follower
// org.apache.zookeeper.server.quorum.LearnerHandler#ping
public void ping() {
long id;
if (syncLimitCheck.check(System.nanoTime())) {
synchronized(leader) {
id = leader.lastProposed;
}
QuorumPacket ping = new QuorumPacket(Leader.PING, id, null, null);
queuePacket(ping);
} else {
LOG.warn("Closing connection to peer due to transaction timeout.");
shutdown();
}
}
如果发现上一条 propose 超时,则断开与 follower 的连接,follower 会 shutdown,然后重新创建对象,重连 leader,会发送 ack 消息
查看事务日志:
org.apache.zookeeper.server.LogFormatter#main
参数 D:/zk_test/data1/version-2/log.100000001
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