diff --git a/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/Deletion.java b/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/Deletion.java
new file mode 100644
index 000000000..c25d5e2b7
--- /dev/null
+++ b/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/Deletion.java
@@ -0,0 +1,45 @@
+/**
+ * Copyright © 2019 Apache IoTDB(incubating) (dev@iotdb.apache.org)
+ * <p>
+ * Licensed 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.engine.modification;
+
+/**
+ * Deletion is a delete operation on a timeseries.
+ */
+public class Deletion extends Modification {
+  private long timestamp;
+
+  public Deletion(String path, long versionNum, long timestamp) {
+    super(Type.DELETION, path, versionNum);
+    this.timestamp = timestamp;
+  }
+
+  public long getTimestamp() {
+    return timestamp;
+  }
+
+  public void setTimestamp(long timestamp) {
+    this.timestamp = timestamp;
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (!(obj instanceof Modification))
+      return false;
+    Deletion del = (Deletion) obj;
+    return super.equals(obj) && del.timestamp == this.timestamp;
+  }
+}
diff --git a/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/Modification.java b/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/Modification.java
new file mode 100644
index 000000000..3504749ad
--- /dev/null
+++ b/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/Modification.java
@@ -0,0 +1,70 @@
+/**
+ * Copyright © 2019 Apache IoTDB(incubating) (dev@iotdb.apache.org)
+ * <p>
+ * Licensed 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.engine.modification;
+
+/**
+ * Modification represents an UPDATE or DELETE operation on a certain timeseries.
+ */
+public abstract class Modification {
+
+  protected Type type;
+  protected String path;
+  protected long versionNum;
+
+  public Modification(Type type, String path, long versionNum) {
+    this.type = type;
+    this.path = path;
+    this.versionNum = versionNum;
+  }
+
+  public String getPath() {
+    return path;
+  }
+
+  public void setPath(String path) {
+    this.path = path;
+  }
+
+  public long getVersionNum() {
+    return versionNum;
+  }
+
+  public void setVersionNum(long versionNum) {
+    this.versionNum = versionNum;
+  }
+
+  public Type getType() {
+    return type;
+  }
+
+  public void setType(Type type) {
+    this.type = type;
+  }
+
+  public enum Type {
+    DELETION
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (!(obj instanceof Modification))
+      return false;
+    Modification mod = (Modification) obj;
+    return mod.type.equals(this.type) && mod.path.equals(this.path)
+            && mod.versionNum == this.versionNum;
+  }
+}
diff --git a/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/ModificationFile.java b/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/ModificationFile.java
new file mode 100644
index 000000000..c04ff1d12
--- /dev/null
+++ b/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/ModificationFile.java
@@ -0,0 +1,101 @@
+/**
+ * Copyright © 2019 Apache IoTDB(incubating) (dev@iotdb.apache.org)
+ * <p>
+ * Licensed 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.engine.modification;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+
+import org.apache.iotdb.db.engine.modification.io.LocalTextModificationAccessor;
+import org.apache.iotdb.db.engine.modification.io.ModificationReader;
+import org.apache.iotdb.db.engine.modification.io.ModificationWriter;
+
+/**
+ * ModificationFile stores the Modifications of a TsFile or unseq file in another file in the same
+ * directory.
+ * Methods in this class are highly synchronized for concurrency safety.
+ */
+public class ModificationFile {
+
+  private Collection<Modification> modifications;
+  private String filePath;
+  private ModificationWriter writer;
+  private ModificationReader reader;
+
+  /**
+   * Construct a ModificationFile using a file as its storage.
+   * @param filePath the path of the storage file.
+   * @throws IOException when IOException raised when
+   */
+  public ModificationFile(String filePath) throws IOException {
+    this.filePath = filePath;
+    LocalTextModificationAccessor accessor = new LocalTextModificationAccessor(filePath);
+    this.writer = accessor;
+    this.reader = accessor;
+  }
+
+  private void init() throws IOException {
+    synchronized (this) {
+      Collection<Modification> mods = reader.read();
+      if (mods == null) {
+        mods = new ArrayList<>();
+      }
+      modifications = mods;
+    }
+  }
+
+  private void checkInit() throws IOException {
+    if (modifications == null) {
+      init();
+    }
+  }
+
+  /**
+   * Release the resources such as streams and caches.
+   */
+  public void close() throws IOException {
+    synchronized (this) {
+      writer.close();
+      modifications = null;
+    }
+  }
+
+  /**
+   * Write a modification in this file. The modification will first be written to the persistent
+   * store then the memory cache.
+   * @param mod the modification to be written.
+   * @throws IOException if IOException is thrown when writing the modification to the store.
+   */
+  public void write(Modification mod) throws IOException {
+    synchronized (this) {
+      checkInit();
+      writer.write(mod);
+      modifications.add(mod);
+    }
+  }
+
+  /**
+   * Get all modifications stored in this file.
+   * @return
+   */
+  public Collection<Modification> getModifications() throws IOException {
+    synchronized (this) {
+      checkInit();
+      return new ArrayList<>(modifications);
+    }
+  }
+}
diff --git a/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/io/LocalTextModificationAccessor.java b/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/io/LocalTextModificationAccessor.java
new file mode 100644
index 000000000..9fd14414e
--- /dev/null
+++ b/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/io/LocalTextModificationAccessor.java
@@ -0,0 +1,135 @@
+/**
+ * Copyright © 2019 Apache IoTDB(incubating) (dev@iotdb.apache.org)
+ * <p>
+ * Licensed 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.engine.modification.io;
+
+import java.io.BufferedReader;
+import java.io.BufferedWriter;
+import java.io.FileNotFoundException;
+import java.io.FileReader;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+
+import org.apache.iotdb.db.engine.modification.Deletion;
+import org.apache.iotdb.db.engine.modification.Modification;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * LocalTextModificationAccessor uses a file on local file system to store the modifications
+ * in text format, and writes modifications by appending to the tail of the file.
+ */
+public class LocalTextModificationAccessor implements ModificationReader, ModificationWriter {
+
+  private static final Logger logger = LoggerFactory.getLogger(LocalTextModificationAccessor.class);
+  private static final String SEPARATOR = ",";
+
+  private String filePath;
+  private BufferedWriter writer;
+
+  /**
+   * Construct a LocalTextModificationAccessor using a file specified by filePath. Only a writer
+   * will be created because the reader will be created only if necessary(call of read()).
+   *
+   * @param filePath the path of the file that is used for storing modifications.
+   * @throws IOException if the writer cannot be created.
+   */
+  public LocalTextModificationAccessor(String filePath) throws IOException {
+    this.filePath = filePath;
+    writer = new BufferedWriter(new FileWriter(filePath));
+  }
+
+  @Override
+  public Collection<Modification> read() throws IOException {
+    BufferedReader reader;
+    try {
+      reader = new BufferedReader(new FileReader(filePath));
+    } catch (FileNotFoundException e) {
+      return null;
+    }
+    String line;
+
+    List<Modification> modificationList = new ArrayList<>();
+    try {
+      while ((line = reader.readLine()) != null) {
+        modificationList.add(decodeModification(line));
+      }
+    } catch (IOException e) {
+      reader.close();
+      logger.error("An error occurred when reading modifications, and the remaining modifications "
+              + "were ignored.", e);
+    }
+    return modificationList;
+  }
+
+  @Override
+  public void close() throws IOException {
+    writer.close();
+  }
+
+  @Override
+  public void write(Modification mod) throws IOException {
+    writer.write(encodeModification(mod));
+    writer.newLine();
+    writer.flush();
+  }
+
+  private static String encodeModification(Modification mod) {
+    if (mod instanceof Deletion)
+      return encodeDeletion((Deletion) mod);
+    return null;
+  }
+
+  private static Modification decodeModification(String src) throws IOException {
+    String[] fields = src.split(SEPARATOR);
+    if (Modification.Type.DELETION.name().equals(fields[0])) {
+      return decodeDeletion(fields);
+    }
+    throw new IOException("Unknown modification type: " + fields[0]);
+  }
+
+  private static String encodeDeletion(Deletion del) {
+    StringBuilder stringBuilder = new StringBuilder();
+    stringBuilder.append(del.getType().toString()).append(SEPARATOR).append(del.getPath())
+            .append(SEPARATOR).append(del.getVersionNum()).append(SEPARATOR)
+            .append(del.getTimestamp());
+    return stringBuilder.toString();
+  }
+
+  private static Deletion decodeDeletion(String[] fields) throws IOException {
+    if (fields.length != 4) {
+      throw new IOException("Incorrect deletion fields number: " + fields.length);
+    }
+
+    String path = fields[1];
+    long versionNum, timestamp;
+    try {
+      versionNum = Long.parseLong(fields[2]);
+    } catch (NumberFormatException e) {
+      throw new IOException("Invalide version number: " + fields[2]);
+    }
+    try {
+      timestamp = Long.parseLong(fields[3]);
+    } catch (NumberFormatException e) {
+      throw new IOException("Invalide timestamp: " + fields[3]);
+    }
+
+    return new Deletion(path, versionNum, timestamp);
+  }
+}
diff --git a/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/io/ModificationReader.java b/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/io/ModificationReader.java
new file mode 100644
index 000000000..d770eccbc
--- /dev/null
+++ b/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/io/ModificationReader.java
@@ -0,0 +1,40 @@
+/**
+ * Copyright © 2019 Apache IoTDB(incubating) (dev@iotdb.apache.org)
+ * <p>
+ * Licensed 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.engine.modification.io;
+
+import java.io.IOException;
+import java.util.Collection;
+
+import org.apache.iotdb.db.engine.modification.Modification;
+
+/**
+ * ModificationReader reads all modifications from a persistent medium like file system.
+ */
+public interface ModificationReader {
+
+  /**
+   * Read all modifications from a persistent medium.
+   *
+   * @return a list of modifications contained the medium.
+   */
+  Collection<Modification> read() throws IOException;
+
+  /**
+   * Release resources like streams.
+   */
+  void close() throws IOException;
+}
diff --git a/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/io/ModificationWriter.java b/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/io/ModificationWriter.java
new file mode 100644
index 000000000..5c3806b3e
--- /dev/null
+++ b/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/io/ModificationWriter.java
@@ -0,0 +1,39 @@
+/**
+ * Copyright © 2019 Apache IoTDB(incubating) (dev@iotdb.apache.org)
+ * <p>
+ * Licensed 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.engine.modification.io;
+
+import java.io.IOException;
+
+import org.apache.iotdb.db.engine.modification.Modification;
+
+/**
+ * ModificationWriter provides methods for writing a modification to a persistent medium like file
+ * system.
+ */
+public interface ModificationWriter {
+
+  /**
+   * Write a new modification to the persistent medium.
+   * @param mod the modification to be written.
+   */
+  void write(Modification mod) throws IOException;
+
+  /**
+   * Release resources like streams.
+   */
+  void close() throws IOException;
+}
diff --git a/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/package-info.java b/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/package-info.java
new file mode 100644
index 000000000..49697e169
--- /dev/null
+++ b/iotdb/src/main/java/org/apache/iotdb/db/engine/modification/package-info.java
@@ -0,0 +1,22 @@
+/**
+ * Copyright © 2019 Apache IoTDB(incubating) (dev@iotdb.apache.org)
+ * <p>
+ * Licensed 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.
+ * <p>
+ * modification is the functional module responsible for processing UPDATE and DELETE.
+ */
+
+/**
+ * modification is the functional module responsible for processing UPDATE and DELETE.
+ */
+package org.apache.iotdb.db.engine.modification;
\ No newline at end of file
diff --git a/iotdb/src/test/java/org/apache/iotdb/db/engine/modification/ModificationFileTest.java b/iotdb/src/test/java/org/apache/iotdb/db/engine/modification/ModificationFileTest.java
new file mode 100644
index 000000000..6907a3d8d
--- /dev/null
+++ b/iotdb/src/test/java/org/apache/iotdb/db/engine/modification/ModificationFileTest.java
@@ -0,0 +1,62 @@
+/**
+ * Copyright © 2019 Apache IoTDB(incubating) (dev@iotdb.apache.org)
+ * <p>
+ * Licensed 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.engine.modification;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.List;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class ModificationFileTest {
+  @Test
+  public void readMyWrite() {
+    String tempFileName = "mod.temp";
+    Modification[] modifications = new Modification[]{
+            new Deletion("p1", 1, 1),
+            new Deletion("p2", 2, 2),
+            new Deletion("p3", 3, 3),
+            new Deletion("p4", 4, 4),
+    };
+    try {
+      ModificationFile mFile = new ModificationFile(tempFileName);
+      for (int i = 0; i < 2; i++) {
+        mFile.write(modifications[i]);
+      }
+      List<Modification> modificationList = (List<Modification>) mFile.getModifications();
+      for (int i = 0; i < 2; i++) {
+        assertEquals(modifications[i], modificationList.get(i));
+      }
+
+      for (int i = 2; i < 4; i++) {
+        mFile.write(modifications[i]);
+      }
+      modificationList = (List<Modification>) mFile.getModifications();
+      for (int i = 0; i < 4; i++) {
+        assertEquals(modifications[i], modificationList.get(i));
+      }
+      mFile.close();
+    } catch (IOException e) {
+      fail(e.getMessage());
+    } finally {
+      new File(tempFileName).delete();
+    }
+  }
+}
\ No newline at end of file
diff --git a/iotdb/src/test/java/org/apache/iotdb/db/engine/modification/io/LocalTextModificationAccessorTest.java b/iotdb/src/test/java/org/apache/iotdb/db/engine/modification/io/LocalTextModificationAccessorTest.java
new file mode 100644
index 000000000..125d243e7
--- /dev/null
+++ b/iotdb/src/test/java/org/apache/iotdb/db/engine/modification/io/LocalTextModificationAccessorTest.java
@@ -0,0 +1,79 @@
+/**
+ * Copyright © 2019 Apache IoTDB(incubating) (dev@iotdb.apache.org)
+ * <p>
+ * Licensed 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.engine.modification.io;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.Collection;
+import java.util.List;
+
+import org.apache.iotdb.db.engine.modification.Deletion;
+import org.apache.iotdb.db.engine.modification.Modification;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class LocalTextModificationAccessorTest {
+
+  @Test
+  public void readMyWrite() {
+    String tempFileName = "mod.temp";
+    Modification[] modifications = new Modification[]{
+            new Deletion("p1", 1, 1),
+            new Deletion("p2", 2, 2),
+            new Deletion("p3", 3, 3),
+            new Deletion("p4", 4, 4),
+    };
+    try {
+      LocalTextModificationAccessor accessor = new LocalTextModificationAccessor(tempFileName);
+      for (int i = 0; i < 2; i++) {
+        accessor.write(modifications[i]);
+      }
+      List<Modification> modificationList = (List<Modification>) accessor.read();
+      for (int i = 0; i < 2; i++) {
+        assertEquals(modifications[i], modificationList.get(i));
+      }
+
+      for (int i = 2; i < 4; i++) {
+        accessor.write(modifications[i]);
+      }
+      modificationList = (List<Modification>) accessor.read();
+      for (int i = 0; i < 4; i++) {
+        assertEquals(modifications[i], modificationList.get(i));
+      }
+      accessor.close();
+    } catch (IOException e) {
+      fail(e.getMessage());
+    } finally {
+      new File(tempFileName).delete();
+    }
+  }
+
+  @Test
+  public void readNull() throws IOException {
+    String tempFileName = "mod.temp";
+    LocalTextModificationAccessor accessor = null;
+    try {
+      accessor = new LocalTextModificationAccessor(tempFileName);
+    } catch (IOException e) {
+      fail(e.getMessage());
+    }
+    new File(tempFileName).delete();
+    Collection<Modification> modifications = accessor.read();
+    assertNull(modifications);
+  }
+}
\ No newline at end of file