hbase replication原理分析

本文只是從總體流程來分析replication過程，很多細節沒有提及，下一篇文章準備多分析分析細節。

replicationSource啟動過程

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階段for循環把所有的replicationPeers添加到source里，即每個replicationPeer對應一個source，也就是可以添加多個slave cluster，replicationPeers從zookeeper /hbase/replication/peers目錄取

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

//在addSource階段生成ReplicationSource并啟動ReplicationSource，ReplicationSource本身是一個線程

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

//ReplicationSource線程啟動，進入while循環工作

replicationSource大致工作流程

1. while(isAlive())進行主體循環
2. 從WAL文件獲取List<WAL.Entry>
3. 通過調用shipEdits方法發送數據
4. 調用replicationEndpoint replicate方法發送數據
5. 最終調用admin.replicateWALEntry通過rpc發送數據

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regionserver如何從slave cluster中選取regionserver當做復制節點

1. replication過程需要連接peer（slave cluster），首先要獲取這個peer所有活著的regionservers
2. 拿到所有regionservers信息之后，開始選擇哪些regionservers作為replication的對象
3. 選哪些regionservers當做sink由peer活著的regionserver個數*ratio（默認值0.1）決定，regionservers先shuffle打亂順序后再截取
4. 如果選擇的sink（regionserver）個數為0，一直等待peer上線，也就是slave cluster沒有啟動的情況
5. 下面源碼可以解釋如何選擇regionserver當做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++;     //倍數最多為默認配置的300倍，也就是每次sleep最長間隔是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);

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??? 總結

1. 每個slave cluster對應一個replicationSource線程，各個slave復制互不干擾
2. 每個replicationSource是單線程進行傳輸數據，改成多線程并發傳可能更好
3. 數據是通過rpc發送過去，調用slave cluster regionserver RSRpcServices的replicateWALEntry方法

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