hbase replication原理分析

本文只是从总体流程来分析replication过程，很多细节没有提及，下一篇文章准备多分析分析细节。

replicationSource启动过程

org.apache.hadoop.hbase.regionserver.HRegionServer#startServiceThreads ->

org.apache.hadoop.hbase.replication.regionserver.Replication#startReplicationService ->

//初始化replicationManager

org.apache.hadoop.hbase.replication.regionserver.ReplicationSourceManager#init ->

//在init阶段for循环把所有的replicationPeers添加到source里，即每个replicationPeer对应一个source，也就是可以添加多个slave cluster，replicationPeers从zookeeper /hbase/replication/peers目录取

org.apache.hadoop.hbase.replication.regionserver.ReplicationSourceManager#addSource ->

//在addSource阶段生成ReplicationSource并启动ReplicationSource，ReplicationSource本身是一个线程

org.apache.hadoop.hbase.replication.regionserver.ReplicationSource#startup

//ReplicationSource线程启动，进入while循环工作

replicationSource大致工作流程

while(isAlive())进行主体循环
从WAL文件获取List<WAL.Entry>
通过调用shipEdits方法发送数据
调用replicationEndpoint replicate方法发送数据
最终调用admin.replicateWALEntry通过rpc发送数据

regionserver如何从slave cluster中选取regionserver当做复制节点

replication过程需要连接peer（slave cluster），首先要获取这个peer所有活着的regionservers
拿到所有regionservers信息之后，开始选择哪些regionservers作为replication的对象
选哪些regionservers当做sink由peer活着的regionserver个数*ratio（默认值0.1）决定，regionservers先shuffle打乱顺序后再截取
如果选择的sink（regionserver）个数为0，一直等待peer上线，也就是slave cluster没有启动的情况
下面源码可以解释如何选择regionserver当做sink

  private void connectToPeers() {getRegionServers();int sleepMultiplier = 1;// Connect to peer cluster first, unless we have to stopwhile (this.isRunning() && replicationSinkMgr.getSinks().size() == 0) {replicationSinkMgr.chooseSinks();if (this.isRunning() && replicationSinkMgr.getSinks().size() == 0) {if (sleepForRetries("Waiting for peers", sleepMultiplier)) {sleepMultiplier++;     //倍数最多为默认配置的300倍，也就是每次sleep最长间隔是300秒
        }}}}void chooseSinks() {List<ServerName> slaveAddresses = endpoint.getRegionServers();Collections.shuffle(slaveAddresses, random);int numSinks = (int) Math.ceil(slaveAddresses.size() * ratio);sinks = slaveAddresses.subList(0, numSinks);lastUpdateToPeers = System.currentTimeMillis();badReportCounts.clear();}/*** Do the sleeping logic* @param msg Why we sleep* @param sleepMultiplier by how many times the default sleeping time is augmented* @return True if <code>sleepMultiplier</code> is &lt; <code>maxRetriesMultiplier</code>*/protected boolean sleepForRetries(String msg, int sleepMultiplier) {try {if (LOG.isTraceEnabled()) {LOG.trace(msg + ", sleeping " + sleepForRetries + " times " + sleepMultiplier);}Thread.sleep(this.sleepForRetries * sleepMultiplier);} catch (InterruptedException e) {LOG.debug("Interrupted while sleeping between retries");}return sleepMultiplier < maxRetriesMultiplier;}this.maxRetriesMultiplier = this.conf.getInt("replication.source.maxretriesmultiplier", 300);
this.ratio = conf.getFloat("replication.source.ratio", DEFAULT_REPLICATION_SOURCE_RATIO);