[GitHub] [incubator-iotdb] LebronAl commented on a change in pull request #1157: [IOTDB-567] Apache IoTDB's Peer Tracker for The Raft Protocol

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LebronAl commented on a change in pull request #1157:
URL: https://github.com/apache/incubator-iotdb/pull/1157#discussion_r421214748



##########
File path: cluster/src/main/java/org/apache/iotdb/cluster/log/catchup/CatchUpTask.java
##########
@@ -0,0 +1,169 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.iotdb.cluster.log.catchup;
+
+import java.io.IOException;
+import java.util.Collections;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicBoolean;
+import org.apache.iotdb.cluster.log.Log;
+import org.apache.iotdb.cluster.log.Snapshot;
+import org.apache.iotdb.cluster.log.logtypes.EmptyContentLog;
+import org.apache.iotdb.cluster.rpc.thrift.AppendEntryRequest;
+import org.apache.iotdb.cluster.rpc.thrift.Node;
+import org.apache.iotdb.cluster.rpc.thrift.RaftService.AsyncClient;
+import org.apache.iotdb.cluster.server.NodeCharacter;
+import org.apache.iotdb.cluster.server.Peer;
+import org.apache.iotdb.cluster.server.RaftServer;
+import org.apache.iotdb.cluster.server.handlers.caller.LogCatchUpHandler;
+import org.apache.iotdb.cluster.server.member.RaftMember;
+import org.apache.thrift.TException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class CatchUpTask implements Runnable {
+
+  private static final Logger logger = LoggerFactory.getLogger(LogCatchUpTask.class);
+
+  private Node node;
+  private Peer peer;
+  private RaftMember raftMember;
+  private Snapshot snapshot;
+  private List<Log> logs;
+
+
+  public CatchUpTask(Node node, Peer peer, RaftMember raftMember) {
+    this.node = node;
+    this.peer = peer;
+    this.raftMember = raftMember;
+    this.logs = Collections.emptyList();
+    this.snapshot = null;
+  }
+
+  boolean checkMatchIndex() throws TException, InterruptedException {
+    AppendEntryRequest request = new AppendEntryRequest();
+    AtomicBoolean isMatch = new AtomicBoolean(false);
+
+    LogCatchUpHandler handler = new LogCatchUpHandler();
+    handler.setAppendSucceed(isMatch);
+    handler.setRaftMember(raftMember);
+    handler.setFollower(node);
+    if (raftMember.getHeader() != null) {
+      request.setHeader(raftMember.getHeader());
+    }
+    request.setLeader(raftMember.getThisNode());
+    // not update follower's commitIndex in order to append the log which index is matchIndex twice
+    request.setLeaderCommit(-1);
+    synchronized (raftMember.getLogManager()) {
+      peer.setNextIndex(raftMember.getLogManager().getLastLogIndex());
+      try {
+        logs = raftMember.getLogManager().getEntries(
+            Math.max(raftMember.getLogManager().getFirstIndex(), peer.getMatchIndex() + 1),
+            peer.getNextIndex() + 1);
+      } catch (Exception e) {
+        logger.error("Unexpected error in logManager's getEntries during matchIndexCheck", e);
+      }
+    }
+
+    int index = logs.size() - 1;
+    EmptyContentLog emptyLog = new EmptyContentLog();
+    while (index >= 0) {
+      Log log = logs.get(index);
+      emptyLog.setCurrLogIndex(log.getCurrLogIndex());
+      emptyLog.setCurrLogTerm(log.getCurrLogTerm());
+      synchronized (raftMember.getTerm()) {
+        // make sure this node is still a leader
+        if (raftMember.getCharacter() != NodeCharacter.LEADER) {
+          logger.debug("Leadership is lost when doing a catch-up to {}, aborting", node);
+          break;
+        }
+        request.setTerm(raftMember.getTerm().get());
+      }
+      if (index > 0) {
+        request.setPrevLogIndex(logs.get(index - 1).getCurrLogIndex());
+        request.setPrevLogTerm(logs.get(index - 1).getCurrLogTerm());
+      } else {
+        request.setPrevLogIndex(log.getCurrLogIndex() - 1);
+        try {
+          request.setPrevLogTerm(raftMember.getLogManager().getTerm(log.getCurrLogIndex() - 1));
+        } catch (Exception e) {
+          logger.error("getTerm failed for newly append entries", e);
+        }
+      }
+
+      handler.setLog(log);
+      request.setEntry(emptyLog.serialize());
+
+      synchronized (isMatch) {
+        AsyncClient client = raftMember.connectNode(node);
+        if (client == null) {
+          break;
+        }
+        client.appendEntry(request, handler);
+        raftMember.getLastCatchUpResponseTime().put(node, System.currentTimeMillis());
+        isMatch.wait(RaftServer.connectionTimeoutInMS);
+      }
+      if (isMatch.get()) {
+        // if follower return RESPONSE.AGREE with this empty log, then start sending real logs from this emptyContentLog's index.
+        // which means the log which index is matchIndex will be send twice, but at the first time it sent an empty log.
+        logs.subList(0, index).clear();
+        if (logger.isDebugEnabled()) {
+          logger.debug("{} makes {} catch up with {} cached logs", raftMember.getName(), node,
+              logs.size());
+        }
+        return false;
+      }
+      index--;

Review comment:
       Inconsistencies are generally rare, and there aren't many missing logs, so this may actually be enough. If a performance bottleneck occurs, I will modify here ~




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