[GitHub] [incubator-iotdb] mychaow commented on a change in pull request #1721: [IOTDB-868] fix comma bug for mlog

[GitBox]

mychaow commented on a change in pull request #1721:
URL: https://github.com/apache/incubator-iotdb/pull/1721#discussion_r486736109



##########
File path: server/src/main/java/org/apache/iotdb/db/writelog/io/LogWriter.java
##########
@@ -41,13 +42,26 @@
   private IoTDBConfig config = IoTDBDescriptor.getInstance().getConfig();
   private ByteBuffer lengthBuffer = ByteBuffer.allocate(4);
   private ByteBuffer checkSumBuffer = ByteBuffer.allocate(8);
+  private long forcePeriodInMs = 0;
 
-  public LogWriter(String logFilePath) {
+  public LogWriter(String logFilePath, long forcePeriodInMs) throws 
FileNotFoundException {
     logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    this.forcePeriodInMs = forcePeriodInMs;
+
+    if (channel == null) {
+      fileOutputStream = new FileOutputStream(logFile, true);
+      channel = fileOutputStream.getChannel();
+    }
   }

Review comment:
       Yes, I will add some comments.

##########
File path: server/src/main/java/org/apache/iotdb/db/conf/IoTDBConfigCheck.java
##########
@@ -203,6 +203,13 @@ public void checkConfig() throws IOException {
       }
       // rename tmpLogFile to mlog
       FileUtils.moveFile(tmpMLogFile, mlogFile);
+
+      File oldMLogFile = SystemFileFactory.INSTANCE.getFile(SCHEMA_DIR + 
File.separator
+          + MetadataConstant.METADATA_OLD_LOG);
+
+      if (oldMLogFile.delete()) {

Review comment:
       yes, thank you for pointing this out.

##########
File path: server/src/main/java/org/apache/iotdb/db/writelog/io/LogWriter.java
##########
@@ -41,13 +42,26 @@
   private IoTDBConfig config = IoTDBDescriptor.getInstance().getConfig();
   private ByteBuffer lengthBuffer = ByteBuffer.allocate(4);
   private ByteBuffer checkSumBuffer = ByteBuffer.allocate(8);
+  private long forcePeriodInMs = 0;
 
-  public LogWriter(String logFilePath) {
+  public LogWriter(String logFilePath, long forcePeriodInMs) throws 
FileNotFoundException {
     logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    this.forcePeriodInMs = forcePeriodInMs;
+
+    if (channel == null) {
+      fileOutputStream = new FileOutputStream(logFile, true);
+      channel = fileOutputStream.getChannel();
+    }
   }
 
-  public LogWriter(File logFile) {
+  public LogWriter(File logFile, long forcePeriodInMs) throws 
FileNotFoundException {
     this.logFile = logFile;
+    this.forcePeriodInMs = forcePeriodInMs;
+
+    if (channel == null) {
+      fileOutputStream = new FileOutputStream(logFile, true);

Review comment:
       I think we should throw the exception for it's not normal, because 
fileoutputstream could create it if not exist.

##########
File path: 
server/src/test/java/org/apache/iotdb/db/integration/IoTDBCreateSnapshotIT.java
##########
@@ -156,4 +178,20 @@ private void checkShowTimeseries(Statement statement) 
throws SQLException {
       Assert.assertEquals(8, cnt);
     }
   }
+
+  private PhysicalPlan convertFromString(String str) {
+    String[] words = str.split(",");
+    if (words[0].equals("2")) {

Review comment:
       ok, thanks!

##########
File path: 
server/src/main/java/org/apache/iotdb/db/sync/receiver/transfer/SyncServiceImpl.java
##########
@@ -272,18 +274,25 @@ public SyncStatus checkDataMD5(String md5OfSender) throws 
TException {
   private void loadMetadata() {
     logger.info("Start to load metadata in sync process.");
     if (currentFile.get().exists()) {
-      try (BufferedReader br = new BufferedReader(
-          new java.io.FileReader(currentFile.get()))) {
-        String metadataOperation;
-        while ((metadataOperation = br.readLine()) != null) {
+      MLogReader mLogReader = null;
+      try {
+        mLogReader = new MLogReader(config.getSchemaDir(), 
MetadataConstant.METADATA_LOG);
+        while (mLogReader.hasNext()) {
+          PhysicalPlan plan = mLogReader.next();
           try {
-            IoTDB.metaManager.operation(metadataOperation);
-          } catch (IOException | MetadataException e) {
-            logger.error("Can not operate metadata operation {} ", 
metadataOperation, e);
+            if (plan == null) {
+              continue;
+            }
+            IoTDB.metaManager.operation(plan);
+          } catch (Exception e) {
+            logger.error("Can not operate metadata operation {} for err:{}", 
plan.getOperatorType(), e);
           }
         }
+        mLogReader.close();
       } catch (IOException e) {
         logger.error("Cannot read the file {}.", 
currentFile.get().getAbsoluteFile(), e);
+      } finally {
+        mLogReader.close();

Review comment:
       yes!

##########
File path: 
server/src/main/java/org/apache/iotdb/db/qp/physical/sys/StorageGroupMNodePlan.java
##########
@@ -0,0 +1,124 @@
+/*
+ * 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.db.qp.physical.sys;
+
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.qp.logical.Operator;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+
+public class StorageGroupMNodePlan extends PhysicalPlan {

Review comment:
       haha, I will change it. It's a mistake.

##########
File path: docs/zh/SystemDesign/SchemaManager/SchemaManager.md
##########
@@ -211,7 +211,7 @@ IoTDB 的元数据管理采用目录树的形式，倒数第二层为设备层
 
 ## 元数据日志管理
 
-* org.apache.iotdb.db.metadata.MLogWriter
+* org.apache.iotdb.db.metadata.logfile.MLogWriter
 
 所有元数据的操作均会记录到元数据日志文件中，此文件默认为 data/system/schema/mlog.txt。

Review comment:
       Got it!

##########
File path: server/src/main/java/org/apache/iotdb/db/conf/IoTDBConfigCheck.java
##########
@@ -203,6 +203,13 @@ public void checkConfig() throws IOException {
       }
       // rename tmpLogFile to mlog
       FileUtils.moveFile(tmpMLogFile, mlogFile);
+
+      File oldMLogFile = SystemFileFactory.INSTANCE.getFile(SCHEMA_DIR + 
File.separator
+          + MetadataConstant.METADATA_OLD_LOG);

Review comment:
       yes, it's no meaning.

##########
File path: server/src/main/java/org/apache/iotdb/db/metadata/MTree.java
##########
@@ -1002,55 +1008,74 @@ private void findNodes(MNode node, PartialPath path, 
List<PartialPath> res, int
   }
 
   public void serializeTo(String snapshotPath) throws IOException {
-    try (BufferedWriter bw = new BufferedWriter(
-        new FileWriter(SystemFileFactory.INSTANCE.getFile(snapshotPath)))) {
-      root.serializeTo(bw);
+    MLogWriter mLogWriter = null;
+    try {
+      mLogWriter = new MLogWriter(snapshotPath);
+      root.serializeTo(mLogWriter);
+    } finally {
+      if (mLogWriter != null) {
+        mLogWriter.close();
+      }
     }
   }
 
   @SuppressWarnings("squid:S3776") // Suppress high Cognitive Complexity 
warning
   public static MTree deserializeFrom(File mtreeSnapshot) {
-    try (BufferedReader br = new BufferedReader(new 
FileReader(mtreeSnapshot))) {
-      String s;
+    MLogReader mlogReader = null;
+    try {

Review comment:
       Got it!

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,350 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.info("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMeasurementMNode(MeasurementMNode node) throws 
IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MeasurementNodePlan plan = new MeasurementNodePlan(node.getName(), 
node.getAlias(),
+        node.getOffset(), childSize, node.getSchema());
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void seriallizeStorageGroupMNode(StorageGroupMNode node) throws 
IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      StorageGroupMNodePlan plan = new StorageGroupMNodePlan(node.getName(), 
node.getDataTTL(), childSize);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public static void upgradeMLog(String schemaDir, String logFileName) throws 
IOException {
+    File logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + 
File.separator + logFileName);
+    File tmpLogFile = 
SystemFileFactory.INSTANCE.getFile(logFile.getAbsolutePath() + ".tmp");
+    File oldLogFile = SystemFileFactory.INSTANCE.getFile(
+        schemaDir + File.separator + MetadataConstant.METADATA_OLD_LOG);
+
+    if (oldLogFile.exists()) {
+      MLogWriter mLogWriter = null;
+      OldMLogReader oldMLogReader = null;
+      try {
+        // upgrade from old character log file to new binary mlog
+        mLogWriter = new MLogWriter(schemaDir, logFileName + ".tmp");
+        oldMLogReader = new OldMLogReader(schemaDir, 
MetadataConstant.METADATA_OLD_LOG);

Review comment:
       Got it!

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,340 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter implements AutoCloseable {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.warn("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);

Review comment:
       It's snapshot file, not mlog.bin, I just serialize the snapshot and mlog 
by the same logwriter.

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,340 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter implements AutoCloseable {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.warn("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);

Review comment:
       It's snapshot file, not mlog.bin, I just serialize the snapshot and mlog 
by the same logwriter class. So, the snapshot file has the same format with 
mlog.bin.

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,350 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.info("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMeasurementMNode(MeasurementMNode node) throws 
IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MeasurementNodePlan plan = new MeasurementNodePlan(node.getName(), 
node.getAlias(),
+        node.getOffset(), childSize, node.getSchema());
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void seriallizeStorageGroupMNode(StorageGroupMNode node) throws 
IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      StorageGroupMNodePlan plan = new StorageGroupMNodePlan(node.getName(), 
node.getDataTTL(), childSize);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public static void upgradeMLog(String schemaDir, String logFileName) throws 
IOException {
+    File logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + 
File.separator + logFileName);
+    File tmpLogFile = 
SystemFileFactory.INSTANCE.getFile(logFile.getAbsolutePath() + ".tmp");
+    File oldLogFile = SystemFileFactory.INSTANCE.getFile(
+        schemaDir + File.separator + MetadataConstant.METADATA_OLD_LOG);
+
+    if (oldLogFile.exists()) {
+      MLogWriter mLogWriter = null;
+      OldMLogReader oldMLogReader = null;
+      try {
+        // upgrade from old character log file to new binary mlog
+        mLogWriter = new MLogWriter(schemaDir, logFileName + ".tmp");
+        oldMLogReader = new OldMLogReader(schemaDir, 
MetadataConstant.METADATA_OLD_LOG);

Review comment:
       Got it!

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,340 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter implements AutoCloseable {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.warn("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);

Review comment:
       It's snapshot file, not mlog.bin, I just serialize the snapshot and mlog 
by the same logwriter.

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,340 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter implements AutoCloseable {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.warn("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);

Review comment:
       It's snapshot file, not mlog.bin, I just serialize the snapshot and mlog 
by the same logwriter class. So, the snapshot file has the same format with 
mlog.bin.

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,350 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.info("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMeasurementMNode(MeasurementMNode node) throws 
IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MeasurementNodePlan plan = new MeasurementNodePlan(node.getName(), 
node.getAlias(),
+        node.getOffset(), childSize, node.getSchema());
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void seriallizeStorageGroupMNode(StorageGroupMNode node) throws 
IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      StorageGroupMNodePlan plan = new StorageGroupMNodePlan(node.getName(), 
node.getDataTTL(), childSize);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public static void upgradeMLog(String schemaDir, String logFileName) throws 
IOException {
+    File logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + 
File.separator + logFileName);
+    File tmpLogFile = 
SystemFileFactory.INSTANCE.getFile(logFile.getAbsolutePath() + ".tmp");
+    File oldLogFile = SystemFileFactory.INSTANCE.getFile(
+        schemaDir + File.separator + MetadataConstant.METADATA_OLD_LOG);
+
+    if (oldLogFile.exists()) {
+      MLogWriter mLogWriter = null;
+      OldMLogReader oldMLogReader = null;
+      try {
+        // upgrade from old character log file to new binary mlog
+        mLogWriter = new MLogWriter(schemaDir, logFileName + ".tmp");
+        oldMLogReader = new OldMLogReader(schemaDir, 
MetadataConstant.METADATA_OLD_LOG);

Review comment:
       Got it!

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,340 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter implements AutoCloseable {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.warn("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);

Review comment:
       It's snapshot file, not mlog.bin, I just serialize the snapshot and mlog 
by the same logwriter.

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,340 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter implements AutoCloseable {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.warn("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);

Review comment:
       It's snapshot file, not mlog.bin, I just serialize the snapshot and mlog 
by the same logwriter class. So, the snapshot file has the same format with 
mlog.bin.

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,350 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.info("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMeasurementMNode(MeasurementMNode node) throws 
IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MeasurementNodePlan plan = new MeasurementNodePlan(node.getName(), 
node.getAlias(),
+        node.getOffset(), childSize, node.getSchema());
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void seriallizeStorageGroupMNode(StorageGroupMNode node) throws 
IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      StorageGroupMNodePlan plan = new StorageGroupMNodePlan(node.getName(), 
node.getDataTTL(), childSize);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public static void upgradeMLog(String schemaDir, String logFileName) throws 
IOException {
+    File logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + 
File.separator + logFileName);
+    File tmpLogFile = 
SystemFileFactory.INSTANCE.getFile(logFile.getAbsolutePath() + ".tmp");
+    File oldLogFile = SystemFileFactory.INSTANCE.getFile(
+        schemaDir + File.separator + MetadataConstant.METADATA_OLD_LOG);
+
+    if (oldLogFile.exists()) {
+      MLogWriter mLogWriter = null;
+      OldMLogReader oldMLogReader = null;
+      try {
+        // upgrade from old character log file to new binary mlog
+        mLogWriter = new MLogWriter(schemaDir, logFileName + ".tmp");
+        oldMLogReader = new OldMLogReader(schemaDir, 
MetadataConstant.METADATA_OLD_LOG);

Review comment:
       Got it!

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,340 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter implements AutoCloseable {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.warn("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);

Review comment:
       It's snapshot file, not mlog.bin, I just serialize the snapshot and mlog 
by the same logwriter.

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,340 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter implements AutoCloseable {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.warn("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);

Review comment:
       It's snapshot file, not mlog.bin, I just serialize the snapshot and mlog 
by the same logwriter class. So, the snapshot file has the same format with 
mlog.bin.

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,350 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.info("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMeasurementMNode(MeasurementMNode node) throws 
IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MeasurementNodePlan plan = new MeasurementNodePlan(node.getName(), 
node.getAlias(),
+        node.getOffset(), childSize, node.getSchema());
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void seriallizeStorageGroupMNode(StorageGroupMNode node) throws 
IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      StorageGroupMNodePlan plan = new StorageGroupMNodePlan(node.getName(), 
node.getDataTTL(), childSize);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public static void upgradeMLog(String schemaDir, String logFileName) throws 
IOException {
+    File logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + 
File.separator + logFileName);
+    File tmpLogFile = 
SystemFileFactory.INSTANCE.getFile(logFile.getAbsolutePath() + ".tmp");
+    File oldLogFile = SystemFileFactory.INSTANCE.getFile(
+        schemaDir + File.separator + MetadataConstant.METADATA_OLD_LOG);
+
+    if (oldLogFile.exists()) {
+      MLogWriter mLogWriter = null;
+      OldMLogReader oldMLogReader = null;
+      try {
+        // upgrade from old character log file to new binary mlog
+        mLogWriter = new MLogWriter(schemaDir, logFileName + ".tmp");
+        oldMLogReader = new OldMLogReader(schemaDir, 
MetadataConstant.METADATA_OLD_LOG);

Review comment:
       Got it!

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,340 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter implements AutoCloseable {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.warn("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);

Review comment:
       It's snapshot file, not mlog.bin, I just serialize the snapshot and mlog 
by the same logwriter.

##########
File path: 
server/src/main/java/org/apache/iotdb/db/metadata/logfile/MLogWriter.java
##########
@@ -0,0 +1,340 @@
+/*
+ * 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.db.metadata.logfile;
+
+import java.io.*;
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
+import java.util.*;
+
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.fileSystem.SystemFileFactory;
+import org.apache.iotdb.db.exception.metadata.MetadataException;
+import org.apache.iotdb.db.metadata.MetadataConstant;
+import org.apache.iotdb.db.metadata.MetadataOperationType;
+import org.apache.iotdb.db.metadata.PartialPath;
+import org.apache.iotdb.db.metadata.mnode.MNode;
+import org.apache.iotdb.db.metadata.mnode.MeasurementMNode;
+import org.apache.iotdb.db.metadata.mnode.StorageGroupMNode;
+import org.apache.iotdb.db.qp.physical.PhysicalPlan;
+import org.apache.iotdb.db.qp.physical.sys.*;
+import org.apache.iotdb.db.writelog.io.LogWriter;
+import org.apache.iotdb.tsfile.file.metadata.enums.CompressionType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSDataType;
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.fileSystem.FSFactoryProducer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class MLogWriter implements AutoCloseable {
+
+  private static final Logger logger = 
LoggerFactory.getLogger(MLogWriter.class);
+  private File logFile;
+  private LogWriter logWriter;
+  private int logNum;
+  private ByteBuffer mlogBuffer = ByteBuffer.allocate(
+    IoTDBDescriptor.getInstance().getConfig().getMlogBufferSize());
+
+  public MLogWriter(String schemaDir, String logFileName) throws IOException {
+    File metadataDir = SystemFileFactory.INSTANCE.getFile(schemaDir);
+    if (!metadataDir.exists()) {
+      if (metadataDir.mkdirs()) {
+        logger.info("create schema folder {}.", metadataDir);
+      } else {
+        logger.warn("create schema folder {} failed.", metadataDir);
+      }
+    }
+
+    logFile = SystemFileFactory.INSTANCE.getFile(schemaDir + File.separator + 
logFileName);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public MLogWriter(String logFilePath) throws IOException {
+    logFile = SystemFileFactory.INSTANCE.getFile(logFilePath);
+    // always flush
+    logWriter = new LogWriter(logFile, 0L);
+  }
+
+  public void close() throws IOException {
+    sync();
+    logWriter.close();
+  }
+
+  private void sync() {
+    try {
+      logWriter.write(mlogBuffer);
+    } catch (IOException e) {
+      logger.error("MLog {} sync failed, change system mode to read-only", 
logFile.getAbsoluteFile(), e);
+      IoTDBDescriptor.getInstance().getConfig().setReadOnly(true);
+    }
+    mlogBuffer.clear();
+  }
+
+  private void putLog(PhysicalPlan plan) {
+    mlogBuffer.mark();
+    try {
+      plan.serialize(mlogBuffer);
+    } catch (BufferOverflowException e) {
+      logger.error("MLog {} BufferOverflow !", plan.getOperatorType(), e);
+      mlogBuffer.reset();
+      sync();
+      plan.serialize(mlogBuffer);
+    }
+    logNum ++;
+  }
+
+  public void createTimeseries(CreateTimeSeriesPlan plan, long offset) throws 
IOException {
+    try {
+      putLog(plan);
+      ChangeTagOffsetPlan changeTagOffsetPlan = new 
ChangeTagOffsetPlan(plan.getPath(), offset);
+      putLog(changeTagOffsetPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteTimeseries(DeleteTimeSeriesPlan deleteTimeSeriesPlan) 
throws IOException {
+    try {
+      putLog(deleteTimeSeriesPlan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      SetStorageGroupPlan plan = new SetStorageGroupPlan(storageGroup);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void deleteStorageGroup(PartialPath storageGroup) throws IOException {
+    try {
+      DeleteStorageGroupPlan plan = new 
DeleteStorageGroupPlan(Collections.singletonList(storageGroup));
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void setTTL(PartialPath storageGroup, long ttl) throws IOException {
+    try {
+      SetTTLPlan plan = new SetTTLPlan(storageGroup, ttl);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeOffset(PartialPath path, long offset) throws IOException {
+    try {
+      ChangeTagOffsetPlan plan = new ChangeTagOffsetPlan(path, offset);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void changeAlias(PartialPath path, String alias) throws IOException {
+    try {
+      ChangeAliasPlan plan = new ChangeAliasPlan(path, alias);
+      putLog(plan);
+    } catch (BufferOverflowException e) {
+      throw new IOException(
+        "Log cannot fit into buffer, please increase mlog_buffer_size", e);
+    }
+  }
+
+  public void serializeMNode(MNode node) throws IOException {
+    try {
+      int childSize = 0;
+      if (node.getChildren() != null) {
+        childSize = node.getChildren().size();
+      }
+      MNodePlan plan = new MNodePlan(node.getName(), childSize);
+      putLog(plan);

Review comment:
       It's snapshot file, not mlog.bin, I just serialize the snapshot and mlog 
by the same logwriter class. So, the snapshot file has the same format with 
mlog.bin.




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