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From aengin...@apache.org
Subject [2/2] hadoop git commit: HDFS-11196. Ozone: Improve logging and error handling in the container layer. Contributed by Anu Engineer.
Date Wed, 08 Mar 2017 17:41:48 GMT
HDFS-11196. Ozone: Improve logging and error handling in the container layer. Contributed by Anu Engineer.


Project: http://git-wip-us.apache.org/repos/asf/hadoop/repo
Commit: http://git-wip-us.apache.org/repos/asf/hadoop/commit/40741236
Tree: http://git-wip-us.apache.org/repos/asf/hadoop/tree/40741236
Diff: http://git-wip-us.apache.org/repos/asf/hadoop/diff/40741236

Branch: refs/heads/HDFS-7240
Commit: 4074123636f2920fadfd464f7a19684cdc817231
Parents: dac2b9e
Author: Anu Engineer <aengineer@apache.org>
Authored: Wed Mar 8 09:36:20 2017 -0800
Committer: Anu Engineer <aengineer@apache.org>
Committed: Wed Mar 8 09:36:20 2017 -0800

----------------------------------------------------------------------
 .../helpers/StorageContainerException.java      | 104 ++++++++++
 .../scm/storage/ContainerProtocolCalls.java     |  60 ++----
 .../main/proto/DatanodeContainerProtocol.proto  |  17 ++
 .../container/common/helpers/ChunkUtils.java    | 117 +++++++----
 .../common/helpers/ContainerUtils.java          |  82 ++++++--
 .../container/common/helpers/KeyUtils.java      |  29 ++-
 .../container/common/impl/ChunkManagerImpl.java |  64 +++---
 .../common/impl/ContainerManagerImpl.java       | 203 ++++++++++++-------
 .../ozone/container/common/impl/Dispatcher.java | 192 ++++++++++--------
 .../container/common/impl/KeyManagerImpl.java   |  74 +++++--
 .../common/interfaces/ChunkManager.java         |  15 +-
 .../common/interfaces/ContainerDispatcher.java  |   6 +-
 .../common/interfaces/ContainerManager.java     |  22 +-
 .../container/common/interfaces/KeyManager.java |  12 +-
 .../ozone/container/ContainerTestHelper.java    |  11 +-
 .../common/impl/TestContainerPersistence.java   |  19 +-
 .../transport/server/TestContainerServer.java   |  16 +-
 .../hadoop/ozone/scm/TestAllocateContainer.java |   9 +-
 .../ozone/scm/TestContainerSmallFile.java       | 131 ++++++++++++
 19 files changed, 819 insertions(+), 364 deletions(-)
----------------------------------------------------------------------


http://git-wip-us.apache.org/repos/asf/hadoop/blob/40741236/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/scm/container/common/helpers/StorageContainerException.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/scm/container/common/helpers/StorageContainerException.java b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/scm/container/common/helpers/StorageContainerException.java
new file mode 100644
index 0000000..549fced
--- /dev/null
+++ b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/scm/container/common/helpers/StorageContainerException.java
@@ -0,0 +1,104 @@
+/*
+ * 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.hadoop.scm.container.common.helpers;
+
+import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos;
+
+import java.io.IOException;
+
+/**
+ * Exceptions thrown from the Storage Container.
+ */
+public class StorageContainerException extends IOException {
+  private ContainerProtos.Result result;
+
+  /**
+   * Constructs an {@code IOException} with {@code null}
+   * as its error detail message.
+   */
+  public StorageContainerException(ContainerProtos.Result result) {
+    this.result = result;
+  }
+
+  /**
+   * Constructs an {@code IOException} with the specified detail message.
+   *
+   * @param message The detail message (which is saved for later retrieval by
+   * the {@link #getMessage()} method)
+   * @param result - The result code
+   */
+  public StorageContainerException(String message,
+      ContainerProtos.Result result) {
+    super(message);
+    this.result = result;
+  }
+
+  /**
+   * Constructs an {@code IOException} with the specified detail message
+   * and cause.
+   * <p>
+   * <p> Note that the detail message associated with {@code cause} is
+   * <i>not</i> automatically incorporated into this exception's detail
+   * message.
+   *
+   * @param message The detail message (which is saved for later retrieval by
+   * the {@link #getMessage()} method)
+   *
+   * @param cause The cause (which is saved for later retrieval by the {@link
+   * #getCause()} method).  (A null value is permitted, and indicates that the
+   * cause is nonexistent or unknown.)
+   *
+   * @param result - The result code
+   * @since 1.6
+   */
+  public StorageContainerException(String message, Throwable cause,
+      ContainerProtos.Result result) {
+    super(message, cause);
+    this.result = result;
+  }
+
+  /**
+   * Constructs an {@code IOException} with the specified cause and a
+   * detail message of {@code (cause==null ? null : cause.toString())}
+   * (which typically contains the class and detail message of {@code cause}).
+   * This constructor is useful for IO exceptions that are little more
+   * than wrappers for other throwables.
+   *
+   * @param cause The cause (which is saved for later retrieval by the {@link
+   * #getCause()} method).  (A null value is permitted, and indicates that the
+   * cause is nonexistent or unknown.)
+   * @param result - The result code
+   * @since 1.6
+   */
+  public StorageContainerException(Throwable cause, ContainerProtos.Result
+      result) {
+    super(cause);
+    this.result = result;
+  }
+
+  /**
+   * Returns Result.
+   *
+   * @return Result.
+   */
+  public ContainerProtos.Result getResult() {
+    return result;
+  }
+
+
+}

http://git-wip-us.apache.org/repos/asf/hadoop/blob/40741236/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/scm/storage/ContainerProtocolCalls.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/scm/storage/ContainerProtocolCalls.java b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/scm/storage/ContainerProtocolCalls.java
index 7fc1fc0..d2c944b 100644
--- a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/scm/storage/ContainerProtocolCalls.java
+++ b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/scm/storage/ContainerProtocolCalls.java
@@ -18,13 +18,7 @@
 
 package org.apache.hadoop.scm.storage;
 
-import static java.net.HttpURLConnection.HTTP_BAD_REQUEST;
-import static java.net.HttpURLConnection.HTTP_INTERNAL_ERROR;
-
-import java.io.IOException;
-
 import com.google.protobuf.ByteString;
-
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos;
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos.ChunkInfo;
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
@@ -35,23 +29,26 @@ import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
     .GetKeyRequestProto;
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
     .GetKeyResponseProto;
+import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .GetSmallFileRequestProto;
+import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .GetSmallFileResponseProto;
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos.KeyData;
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
     .PutKeyRequestProto;
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .PutSmallFileRequestProto;
+import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
     .ReadChunkRequestProto;
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
     .ReadChunkResponseProto;
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos.Type;
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
     .WriteChunkRequestProto;
-import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
-    .PutSmallFileRequestProto;
-import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
-    .GetSmallFileResponseProto;
-import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
-    .GetSmallFileRequestProto;
 import org.apache.hadoop.scm.XceiverClient;
+import org.apache.hadoop.scm.container.common.helpers.StorageContainerException;
+
+import java.io.IOException;
 
 /**
  * Implementation of all container protocol calls performed by Container
@@ -87,7 +84,7 @@ public final class ContainerProtocolCalls {
         .setGetKey(readKeyRequest)
         .build();
     ContainerCommandResponseProto response = xceiverClient.sendCommand(request);
-    validateContainerResponse(response, traceID);
+    validateContainerResponse(response);
     return response.getGetKey();
   }
 
@@ -112,7 +109,7 @@ public final class ContainerProtocolCalls {
         .setPutKey(createKeyRequest)
         .build();
     ContainerCommandResponseProto response = xceiverClient.sendCommand(request);
-    validateContainerResponse(response, traceID);
+    validateContainerResponse(response);
   }
 
   /**
@@ -140,7 +137,7 @@ public final class ContainerProtocolCalls {
         .setReadChunk(readChunkRequest)
         .build();
     ContainerCommandResponseProto response = xceiverClient.sendCommand(request);
-    validateContainerResponse(response, traceID);
+    validateContainerResponse(response);
     return response.getReadChunk();
   }
 
@@ -170,7 +167,7 @@ public final class ContainerProtocolCalls {
         .setWriteChunk(writeChunkRequest)
         .build();
     ContainerCommandResponseProto response = xceiverClient.sendCommand(request);
-    validateContainerResponse(response, traceID);
+    validateContainerResponse(response);
   }
 
   /**
@@ -218,7 +215,7 @@ public final class ContainerProtocolCalls {
         .setPutSmallFile(putSmallFileRequest)
         .build();
     ContainerCommandResponseProto response = client.sendCommand(request);
-    validateContainerResponse(response, traceID);
+    validateContainerResponse(response);
   }
 
   /**
@@ -245,7 +242,7 @@ public final class ContainerProtocolCalls {
     request.setTraceID(traceID);
     ContainerCommandResponseProto response = client.sendCommand(
         request.build());
-    validateContainerResponse(response, traceID);
+    validateContainerResponse(response);
   }
 
   /**
@@ -280,7 +277,7 @@ public final class ContainerProtocolCalls {
         .setGetSmallFile(getSmallFileRequest)
         .build();
     ContainerCommandResponseProto response = client.sendCommand(request);
-    validateContainerResponse(response, traceID);
+    validateContainerResponse(response);
     return response.getGetSmallFile();
   }
 
@@ -289,28 +286,15 @@ public final class ContainerProtocolCalls {
    * return code is mapped to a corresponding exception and thrown.
    *
    * @param response container protocol call response
-   * @param traceID container protocol call args
    * @throws IOException if the container protocol call failed
    */
   private static void validateContainerResponse(
-      ContainerCommandResponseProto response, String traceID
-  ) throws IOException {
-    // TODO : throw the right type of exception
-    switch (response.getResult()) {
-    case SUCCESS:
-      break;
-    case MALFORMED_REQUEST:
-      throw new IOException(HTTP_BAD_REQUEST +
-          ":Bad container request: " + traceID);
-    case UNSUPPORTED_REQUEST:
-      throw new IOException(HTTP_INTERNAL_ERROR +
-          "Unsupported container request: " + traceID);
-    case CONTAINER_INTERNAL_ERROR:
-      throw new IOException(HTTP_INTERNAL_ERROR +
-          "Container internal error:" + traceID);
-    default:
-      throw new IOException(HTTP_INTERNAL_ERROR +
-          "Unrecognized container response:" + traceID);
+      ContainerCommandResponseProto response
+  ) throws StorageContainerException {
+    if (response.getResult() == ContainerProtos.Result.SUCCESS) {
+      return;
     }
+    throw new StorageContainerException(
+        response.getMessage(), response.getResult());
   }
 }

http://git-wip-us.apache.org/repos/asf/hadoop/blob/40741236/hadoop-hdfs-project/hadoop-hdfs-client/src/main/proto/DatanodeContainerProtocol.proto
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/proto/DatanodeContainerProtocol.proto b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/proto/DatanodeContainerProtocol.proto
index ee36009..6566a71 100644
--- a/hadoop-hdfs-project/hadoop-hdfs-client/src/main/proto/DatanodeContainerProtocol.proto
+++ b/hadoop-hdfs-project/hadoop-hdfs-client/src/main/proto/DatanodeContainerProtocol.proto
@@ -99,6 +99,23 @@ enum Result {
   UNSUPPORTED_REQUEST = 2;
   MALFORMED_REQUEST = 3;
   CONTAINER_INTERNAL_ERROR = 4;
+  INVALID_CONFIG = 5;
+  INVALID_FILE_HASH_FOUND = 6;
+  CONTAINER_EXISTS = 7;
+  NO_SUCH_ALGORITHM = 8;
+  CONTAINER_NOT_FOUND = 9;
+  IO_EXCEPTION = 10;
+  UNABLE_TO_READ_METADATA_DB = 11;
+  NO_SUCH_KEY = 12;
+  OVERWRITE_FLAG_REQUIRED = 13;
+  UNABLE_TO_FIND_DATA_DIR = 14;
+  INVALID_WRITE_SIZE = 15;
+  CHECKSUM_MISMATCH = 16;
+  UNABLE_TO_FIND_CHUNK = 17;
+  PROTOC_DECODING_ERROR = 18;
+  INVALID_ARGUMENT = 19;
+  PUT_SMALL_FILE_ERROR = 20;
+  GET_SMALL_FILE_ERROR = 21;
 }
 
 message ContainerCommandRequestProto {

http://git-wip-us.apache.org/repos/asf/hadoop/blob/40741236/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/ChunkUtils.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/ChunkUtils.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/ChunkUtils.java
index a38567b..277fa18 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/ChunkUtils.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/ChunkUtils.java
@@ -24,6 +24,7 @@ import org.apache.commons.codec.digest.DigestUtils;
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos;
 import org.apache.hadoop.io.IOUtils;
 import org.apache.hadoop.ozone.OzoneConsts;
+import org.apache.hadoop.scm.container.common.helpers.StorageContainerException;
 import org.apache.hadoop.ozone.container.common.impl.ChunkManagerImpl;
 import org.apache.hadoop.scm.container.common.helpers.Pipeline;
 import org.slf4j.Logger;
@@ -39,6 +40,23 @@ import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.util.concurrent.ExecutionException;
 
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.CHECKSUM_MISMATCH;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.CONTAINER_INTERNAL_ERROR;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.CONTAINER_NOT_FOUND;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.INVALID_WRITE_SIZE;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.IO_EXCEPTION;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.OVERWRITE_FLAG_REQUIRED;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.UNABLE_TO_FIND_CHUNK;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.UNABLE_TO_FIND_DATA_DIR;
+
 /**
  * Set of utility functions used by the chunk Manager.
  */
@@ -87,13 +105,13 @@ public final class ChunkUtils {
    * expected to write data to.
    *
    * @param pipeline - pipeline.
-   * @param data     - container data.
-   * @param info     - chunk info.
+   * @param data - container data.
+   * @param info - chunk info.
    * @return File
-   * @throws IOException
+   * @throws StorageContainerException
    */
   public static File validateChunk(Pipeline pipeline, ContainerData data,
-                                   ChunkInfo info) throws IOException {
+      ChunkInfo info) throws StorageContainerException {
 
     Logger log = LoggerFactory.getLogger(ChunkManagerImpl.class);
 
@@ -102,8 +120,9 @@ public final class ChunkUtils {
       if (!ChunkUtils.isOverWritePermitted(info)) {
         log.error("Rejecting write chunk request. Chunk overwrite " +
             "without explicit request. {}", info.toString());
-        throw new IOException("Rejecting write chunk request. OverWrite " +
-            "flag required." + info.toString());
+        throw new StorageContainerException("Rejecting write chunk request. " +
+            "OverWrite flag required." + info.toString(),
+            OVERWRITE_FLAG_REQUIRED);
       }
     }
     return chunkFile;
@@ -113,25 +132,27 @@ public final class ChunkUtils {
    * Validates that Path to chunk file exists.
    *
    * @param pipeline - Container Info.
-   * @param data     - Container Data
-   * @param info     - Chunk info
+   * @param data - Container Data
+   * @param info - Chunk info
    * @return - File.
-   * @throws IOException
+   * @throws StorageContainerException
    */
   public static File getChunkFile(Pipeline pipeline, ContainerData data,
-                                  ChunkInfo info) throws IOException {
+      ChunkInfo info) throws StorageContainerException {
 
     Logger log = LoggerFactory.getLogger(ChunkManagerImpl.class);
     if (data == null) {
       log.error("Invalid container Name: {}", pipeline.getContainerName());
-      throw new IOException("Unable to find the container Name: " +
-          pipeline.getContainerName());
+      throw new StorageContainerException("Unable to find the container Name:" +
+          " " +
+          pipeline.getContainerName(), CONTAINER_NOT_FOUND);
     }
 
     File dataDir = ContainerUtils.getDataDirectory(data).toFile();
     if (!dataDir.exists()) {
       log.error("Unable to find the data directory: {}", dataDir);
-      throw new IOException("Unable to find the data directory: " + dataDir);
+      throw new StorageContainerException("Unable to find the data directory:" +
+          " " + dataDir, UNABLE_TO_FIND_DATA_DIR);
     }
 
     return dataDir.toPath().resolve(info.getChunkName()).toFile();
@@ -143,11 +164,12 @@ public final class ChunkUtils {
    *
    * @param chunkFile - File to write data to.
    * @param chunkInfo - Data stream to write.
-   * @throws IOException
+   * @param data - The data buffer.
+   * @throws StorageContainerException
    */
   public static void writeData(File chunkFile, ChunkInfo chunkInfo,
-                               byte[] data)
-      throws IOException, ExecutionException, InterruptedException,
+      byte[] data) throws
+      StorageContainerException, ExecutionException, InterruptedException,
       NoSuchAlgorithmException {
 
     Logger log = LoggerFactory.getLogger(ChunkManagerImpl.class);
@@ -156,7 +178,7 @@ public final class ChunkUtils {
               "specified. DataLen: %d Byte Array: %d",
           chunkInfo.getLen(), data.length);
       log.error(err);
-      throw new IOException(err);
+      throw new StorageContainerException(err, INVALID_WRITE_SIZE);
     }
 
     AsynchronousFileChannel file = null;
@@ -175,15 +197,24 @@ public final class ChunkUtils {
         verifyChecksum(chunkInfo, data, log);
       }
       int size = file.write(ByteBuffer.wrap(data), chunkInfo.getOffset()).get();
-      if(size != data.length) {
-        log.error("Invalid write size found. Size:{}  Expected: {} " , size,
+      if (size != data.length) {
+        log.error("Invalid write size found. Size:{}  Expected: {} ", size,
             data.length);
-        throw new IOException("Invalid write size found. Size: " + size
-            + " Expected: " + data.length);
+        throw new StorageContainerException("Invalid write size found. " +
+            "Size: " + size + " Expected: " + data.length, INVALID_WRITE_SIZE);
       }
+    } catch (IOException e) {
+      throw new StorageContainerException(e, IO_EXCEPTION);
+
     } finally {
       if (lock != null) {
-        lock.release();
+        try {
+          lock.release();
+        } catch (IOException e) {
+          log.error("Unable to release lock ??, Fatal Error.");
+          throw new StorageContainerException(e, CONTAINER_INTERNAL_ERROR);
+
+        }
       }
       if (file != null) {
         IOUtils.closeStream(file);
@@ -195,22 +226,22 @@ public final class ChunkUtils {
    * Verifies the checksum of a chunk against the data buffer.
    *
    * @param chunkInfo - Chunk Info.
-   * @param data      - data buffer
-   * @param log       - log
+   * @param data - data buffer
+   * @param log - log
    * @throws NoSuchAlgorithmException
-   * @throws IOException
+   * @throws StorageContainerException
    */
   private static void verifyChecksum(ChunkInfo chunkInfo, byte[] data, Logger
-      log) throws NoSuchAlgorithmException, IOException {
+      log) throws NoSuchAlgorithmException, StorageContainerException {
     MessageDigest sha = MessageDigest.getInstance(OzoneConsts.FILE_HASH);
     sha.update(data);
     if (!Hex.encodeHexString(sha.digest()).equals(
         chunkInfo.getChecksum())) {
       log.error("Checksum mismatch. Provided: {} , computed: {}",
           chunkInfo.getChecksum(), DigestUtils.sha256Hex(sha.digest()));
-      throw new IOException("Checksum mismatch. Provided: " +
+      throw new StorageContainerException("Checksum mismatch. Provided: " +
           chunkInfo.getChecksum() + " , computed: " +
-          DigestUtils.sha256Hex(sha.digest()));
+          DigestUtils.sha256Hex(sha.digest()), CHECKSUM_MISMATCH);
     }
   }
 
@@ -218,22 +249,25 @@ public final class ChunkUtils {
    * Reads data from an existing chunk file.
    *
    * @param chunkFile - file where data lives.
-   * @param data      - chunk definition.
+   * @param data - chunk definition.
+   *
    * @return ByteBuffer
-   * @throws IOException
+   *
+   * @throws StorageContainerException
    * @throws ExecutionException
    * @throws InterruptedException
    */
   public static ByteBuffer readData(File chunkFile, ChunkInfo data) throws
-      IOException, ExecutionException, InterruptedException,
+      StorageContainerException, ExecutionException, InterruptedException,
       NoSuchAlgorithmException {
     Logger log = LoggerFactory.getLogger(ChunkManagerImpl.class);
 
     if (!chunkFile.exists()) {
       log.error("Unable to find the chunk file. chunk info : {}",
           data.toString());
-      throw new IOException("Unable to find the chunk file. chunk info " +
-          data.toString());
+      throw new StorageContainerException("Unable to find the chunk file. " +
+          "chunk info " +
+          data.toString(), UNABLE_TO_FIND_CHUNK);
     }
 
     AsynchronousFileChannel file = null;
@@ -252,9 +286,15 @@ public final class ChunkUtils {
       }
 
       return buf;
+    } catch (IOException e) {
+      throw new StorageContainerException(e, IO_EXCEPTION);
     } finally {
       if (lock != null) {
-        lock.release();
+        try {
+          lock.release();
+        } catch (IOException e) {
+          log.error("I/O error is lock release.");
+        }
       }
       if (file != null) {
         IOUtils.closeStream(file);
@@ -276,14 +316,15 @@ public final class ChunkUtils {
 
   /**
    * Gets a response to the read chunk calls.
+   *
    * @param msg - Msg
-   * @param data  - Data
-   * @param info  - Info
-   * @return    Response.
+   * @param data - Data
+   * @param info - Info
+   * @return Response.
    */
   public static ContainerProtos.ContainerCommandResponseProto
       getReadChunkResponse(ContainerProtos.ContainerCommandRequestProto msg,
-                           byte[] data, ChunkInfo info) {
+      byte[] data, ChunkInfo info) {
     Preconditions.checkNotNull(msg);
 
     ContainerProtos.ReadChunkResponseProto.Builder response =

http://git-wip-us.apache.org/repos/asf/hadoop/blob/40741236/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/ContainerUtils.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/ContainerUtils.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/ContainerUtils.java
index 03d85a8..4aff972 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/ContainerUtils.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/ContainerUtils.java
@@ -25,6 +25,7 @@ import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos;
 import org.apache.hadoop.ozone.OzoneConsts;
 import org.apache.hadoop.ozone.container.common.impl.ContainerManagerImpl;
 import org.apache.hadoop.utils.LevelDBStore;
+import org.apache.hadoop.scm.container.common.helpers.StorageContainerException;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -34,6 +35,10 @@ import java.nio.file.Path;
 import java.nio.file.Paths;
 
 import static org.apache.commons.io.FilenameUtils.removeExtension;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.INVALID_ARGUMENT;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.UNABLE_TO_FIND_DATA_DIR;
 import static org.apache.hadoop.ozone.OzoneConsts.CONTAINER_EXTENSION;
 import static org.apache.hadoop.ozone.OzoneConsts.CONTAINER_META;
 
@@ -42,6 +47,10 @@ import static org.apache.hadoop.ozone.OzoneConsts.CONTAINER_META;
  */
 public final class ContainerUtils {
 
+  private ContainerUtils() {
+    //never constructed.
+  }
+
   /**
    * Returns a CreateContainer Response. This call is used by create and delete
    * containers which have null success responses.
@@ -59,13 +68,13 @@ public final class ContainerUtils {
   /**
    * Returns a ReadContainer Response.
    *
-   * @param msg           Request
+   * @param msg Request
    * @param containerData - data
    * @return Response.
    */
   public static ContainerProtos.ContainerCommandResponseProto
       getReadContainerResponse(ContainerProtos.ContainerCommandRequestProto msg,
-                           ContainerData containerData) {
+      ContainerData containerData) {
     Preconditions.checkNotNull(containerData);
 
     ContainerProtos.ReadContainerResponseProto.Builder response =
@@ -82,14 +91,14 @@ public final class ContainerUtils {
    * We found a command type but no associated payload for the command. Hence
    * return malformed Command as response.
    *
-   * @param msg     - Protobuf message.
-   * @param result  - result
+   * @param msg - Protobuf message.
+   * @param result - result
    * @param message - Error message.
    * @return ContainerCommandResponseProto - MALFORMED_REQUEST.
    */
   public static ContainerProtos.ContainerCommandResponseProto.Builder
       getContainerResponse(ContainerProtos.ContainerCommandRequestProto msg,
-                       ContainerProtos.Result result, String message) {
+      ContainerProtos.Result result, String message) {
     return
         ContainerProtos.ContainerCommandResponseProto.newBuilder()
             .setCmdType(msg.getCmdType())
@@ -99,6 +108,37 @@ public final class ContainerUtils {
   }
 
   /**
+   * Logs the error and returns a response to the caller.
+   *
+   * @param log - Logger
+   * @param ex - Exception
+   * @param msg - Request Object
+   * @return Response
+   */
+  public static ContainerProtos.ContainerCommandResponseProto logAndReturnError(
+      Logger log, StorageContainerException ex,
+      ContainerProtos.ContainerCommandRequestProto msg) {
+    log.info("Trace ID: {} : Message: {} : Result: {}", msg.getTraceID(),
+        ex.getMessage(), ex.getResult().getValueDescriptor().getName());
+    return getContainerResponse(msg, ex.getResult(), ex.getMessage()).build();
+  }
+
+  /**
+   * Logs the error and returns a response to the caller.
+   *
+   * @param log - Logger
+   * @param ex - Exception
+   * @param msg - Request Object
+   * @return Response
+   */
+  public static ContainerProtos.ContainerCommandResponseProto logAndReturnError(
+      Logger log, RuntimeException ex,
+      ContainerProtos.ContainerCommandRequestProto msg) {
+    log.info("Trace ID: {} : Message: {} ", msg.getTraceID(), ex.getMessage());
+    return getContainerResponse(msg, INVALID_ARGUMENT, ex.getMessage()).build();
+  }
+
+  /**
    * We found a command type but no associated payload for the command. Hence
    * return malformed Command as response.
    *
@@ -133,14 +173,13 @@ public final class ContainerUtils {
     Preconditions.checkNotNull(containerFile);
     return Paths.get(containerFile.getParent()).resolve(
         removeExtension(containerFile.getName())).toString();
-
   }
 
   /**
    * Verifies that this in indeed a new container.
    *
    * @param containerFile - Container File to verify
-   * @param metadataFile  - metadata File to verify
+   * @param metadataFile - metadata File to verify
    * @throws IOException
    */
   public static void verifyIsNewContainer(File containerFile, File metadataFile)
@@ -227,11 +266,11 @@ public final class ContainerUtils {
    * Returns Metadata location.
    *
    * @param containerData - Data
-   * @param location      - Path
+   * @param location - Path
    * @return Path
    */
   public static File getMetadataFile(ContainerData containerData,
-                                     Path location) {
+      Path location) {
     return location.resolve(containerData
         .getContainerName().concat(CONTAINER_META))
         .toFile();
@@ -239,12 +278,13 @@ public final class ContainerUtils {
 
   /**
    * Returns container file location.
-   * @param containerData  - Data
+   *
+   * @param containerData - Data
    * @param location - Root path
    * @return Path
    */
   public static File getContainerFile(ContainerData containerData,
-                                      Path location) {
+      Path location) {
     return location.resolve(containerData
         .getContainerName().concat(CONTAINER_EXTENSION))
         .toFile();
@@ -252,6 +292,7 @@ public final class ContainerUtils {
 
   /**
    * Container metadata directory -- here is where the level DB lives.
+   *
    * @param cData - cData.
    * @return Path to the parent directory where the DB lives.
    */
@@ -264,20 +305,23 @@ public final class ContainerUtils {
 
   /**
    * Returns the path where data or chunks live for a given container.
+   *
    * @param cData - cData container
    * @return - Path
+   * @throws StorageContainerException
    */
-  public static Path getDataDirectory(ContainerData cData) throws IOException {
+  public static Path getDataDirectory(ContainerData cData)
+      throws StorageContainerException {
     Path path = getMetadataDirectory(cData);
     Preconditions.checkNotNull(path);
-    path = path.getParent();
-    if(path == null) {
-      throw new IOException("Unable to get Data directory. null path found");
+    Path parentPath = path.getParent();
+    if (parentPath == null) {
+      throw new StorageContainerException("Unable to get Data directory."
+          + path, UNABLE_TO_FIND_DATA_DIR);
     }
-    return path.resolve(OzoneConsts.CONTAINER_DATA_PATH);
+    return parentPath.resolve(OzoneConsts.CONTAINER_DATA_PATH);
   }
 
-
   /**
    * remove Container if it is empty.
    * <p/>
@@ -323,8 +367,4 @@ public final class ContainerUtils {
     FileUtils.forceDelete(containerPath.toFile());
     FileUtils.forceDelete(metaPath.toFile());
   }
-
-  private ContainerUtils() {
-    //never constructed.
-  }
 }

http://git-wip-us.apache.org/repos/asf/hadoop/blob/40741236/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/KeyUtils.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/KeyUtils.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/KeyUtils.java
index 46473d4..b6be404 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/KeyUtils.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/helpers/KeyUtils.java
@@ -19,6 +19,7 @@ package org.apache.hadoop.ozone.container.common.helpers;
 
 import com.google.common.base.Preconditions;
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos;
+import org.apache.hadoop.scm.container.common.helpers.StorageContainerException;
 import org.apache.hadoop.ozone.container.common.impl.KeyManagerImpl;
 import org.apache.hadoop.ozone.container.common.utils.ContainerCache;
 import org.apache.hadoop.utils.LevelDBStore;
@@ -29,6 +30,9 @@ import java.io.File;
 import java.io.IOException;
 import java.nio.charset.Charset;
 
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.UNABLE_TO_READ_METADATA_DB;
+
 /**
  * Utils functions to help key functions.
  */
@@ -60,18 +64,25 @@ public final class KeyUtils {
    * @param container - container.
    * @param cache     - cache
    * @return LevelDB handle.
-   * @throws IOException
+   * @throws StorageContainerException
    */
   public static LevelDBStore getDB(ContainerData container,
-                                   ContainerCache cache) throws IOException {
+                                   ContainerCache cache)
+      throws StorageContainerException {
     Preconditions.checkNotNull(container);
     Preconditions.checkNotNull(cache);
-    LevelDBStore db = cache.getDB(container.getContainerName());
-    if (db == null) {
-      db = getDB(container.getDBPath());
-      cache.putDB(container.getContainerName(), db);
+    try {
+      LevelDBStore db = cache.getDB(container.getContainerName());
+      if (db == null) {
+        db = getDB(container.getDBPath());
+        cache.putDB(container.getContainerName(), db);
+      }
+      return db;
+    } catch (IOException ex) {
+      String message = "Unable to open DB. DB Name: %s, Path: %s. ex: %s"
+          .format(container.getContainerName(), container.getDBPath(), ex);
+      throw new StorageContainerException(message, UNABLE_TO_READ_METADATA_DB);
     }
-    return db;
   }
 
   /**
@@ -107,8 +118,8 @@ public final class KeyUtils {
 
 
   public static ContainerProtos.ContainerCommandResponseProto
-      getKeyDataResponse(ContainerProtos.ContainerCommandRequestProto msg
-                       , KeyData data) {
+      getKeyDataResponse(ContainerProtos.ContainerCommandRequestProto msg,
+      KeyData data) {
     ContainerProtos.GetKeyResponseProto.Builder getKey = ContainerProtos
         .GetKeyResponseProto.newBuilder();
     getKey.setKeyData(data.getProtoBufMessage());

http://git-wip-us.apache.org/repos/asf/hadoop/blob/40741236/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/ChunkManagerImpl.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/ChunkManagerImpl.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/ChunkManagerImpl.java
index 9a04a77..cace6c9 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/ChunkManagerImpl.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/ChunkManagerImpl.java
@@ -19,19 +19,24 @@ package org.apache.hadoop.ozone.container.common.impl;
 
 import com.google.common.base.Preconditions;
 import org.apache.hadoop.fs.FileUtil;
+import org.apache.hadoop.scm.container.common.helpers.StorageContainerException;
 import org.apache.hadoop.ozone.container.common.helpers.ChunkInfo;
 import org.apache.hadoop.ozone.container.common.helpers.ChunkUtils;
-import org.apache.hadoop.scm.container.common.helpers.Pipeline;
 import org.apache.hadoop.ozone.container.common.interfaces.ChunkManager;
 import org.apache.hadoop.ozone.container.common.interfaces.ContainerManager;
+import org.apache.hadoop.scm.container.common.helpers.Pipeline;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import java.io.File;
-import java.io.IOException;
 import java.security.NoSuchAlgorithmException;
 import java.util.concurrent.ExecutionException;
 
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.CONTAINER_INTERNAL_ERROR;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.UNSUPPORTED_REQUEST;
+
 /**
  * An implementation of ChunkManager that is used by default in ozone.
  */
@@ -54,34 +59,36 @@ public class ChunkManagerImpl implements ChunkManager {
    * writes a given chunk.
    *
    * @param pipeline - Name and the set of machines that make this container.
-   * @param keyName  - Name of the Key.
-   * @param info     - ChunkInfo.
-   * @throws IOException
+   * @param keyName - Name of the Key.
+   * @param info - ChunkInfo.
+   * @throws StorageContainerException
    */
   @Override
   public void writeChunk(Pipeline pipeline, String keyName, ChunkInfo info,
-                         byte[] data)
-      throws IOException {
+      byte[] data)
+      throws StorageContainerException {
 
     // we don't want container manager to go away while we are writing chunks.
     containerManager.readLock();
 
     // TODO : Take keyManager Write lock here.
     try {
-      Preconditions.checkNotNull(pipeline);
-      Preconditions.checkNotNull(pipeline.getContainerName());
+      Preconditions.checkNotNull(pipeline, "Pipeline cannot be null");
+      Preconditions.checkNotNull(pipeline.getContainerName(),
+          "Container name cannot be null");
       File chunkFile = ChunkUtils.validateChunk(pipeline,
           containerManager.readContainer(pipeline.getContainerName()), info);
       ChunkUtils.writeData(chunkFile, info, data);
 
-    } catch (ExecutionException |
-        NoSuchAlgorithmException e) {
+    } catch (ExecutionException | NoSuchAlgorithmException e) {
       LOG.error("write data failed. error: {}", e);
-      throw new IOException("Internal error: ", e);
+      throw new StorageContainerException("Internal error: ", e,
+          CONTAINER_INTERNAL_ERROR);
     } catch (InterruptedException e) {
       Thread.currentThread().interrupt();
       LOG.error("write data failed. error: {}", e);
-      throw new IOException("Internal error: ", e);
+      throw new StorageContainerException("Internal error: ", e,
+          CONTAINER_INTERNAL_ERROR);
     } finally {
       containerManager.readUnlock();
     }
@@ -91,16 +98,16 @@ public class ChunkManagerImpl implements ChunkManager {
    * reads the data defined by a chunk.
    *
    * @param pipeline - container pipeline.
-   * @param keyName  - Name of the Key
-   * @param info     - ChunkInfo.
+   * @param keyName - Name of the Key
+   * @param info - ChunkInfo.
    * @return byte array
-   * @throws IOException TODO: Right now we do not support partial reads and
-   *                     writes of chunks. TODO: Explore if we need to do that
-   *                     for ozone.
+   * @throws StorageContainerException
+   * TODO: Right now we do not support partial reads and writes of chunks.
+   * TODO: Explore if we need to do that for ozone.
    */
   @Override
   public byte[] readChunk(Pipeline pipeline, String keyName, ChunkInfo info)
-      throws IOException {
+      throws StorageContainerException {
     containerManager.readLock();
     try {
       File chunkFile = ChunkUtils.getChunkFile(pipeline, containerManager
@@ -108,11 +115,13 @@ public class ChunkManagerImpl implements ChunkManager {
       return ChunkUtils.readData(chunkFile, info).array();
     } catch (ExecutionException | NoSuchAlgorithmException e) {
       LOG.error("read data failed. error: {}", e);
-      throw new IOException("Internal error: ", e);
+      throw new StorageContainerException("Internal error: ",
+          e, CONTAINER_INTERNAL_ERROR);
     } catch (InterruptedException e) {
       Thread.currentThread().interrupt();
       LOG.error("read data failed. error: {}", e);
-      throw new IOException("Internal error: ", e);
+      throw new StorageContainerException("Internal error: ",
+          e, CONTAINER_INTERNAL_ERROR);
     } finally {
       containerManager.readUnlock();
     }
@@ -122,13 +131,13 @@ public class ChunkManagerImpl implements ChunkManager {
    * Deletes a given chunk.
    *
    * @param pipeline - Pipeline.
-   * @param keyName  - Key Name
-   * @param info     - Chunk Info
-   * @throws IOException
+   * @param keyName - Key Name
+   * @param info - Chunk Info
+   * @throws StorageContainerException
    */
   @Override
   public void deleteChunk(Pipeline pipeline, String keyName, ChunkInfo info)
-      throws IOException {
+      throws StorageContainerException {
 
     containerManager.readLock();
     try {
@@ -139,8 +148,9 @@ public class ChunkManagerImpl implements ChunkManager {
       } else {
         LOG.error("Not Supported Operation. Trying to delete a " +
             "chunk that is in shared file. chunk info : " + info.toString());
-        throw new IOException("Not Supported Operation. Trying to delete a " +
-            "chunk that is in shared file. chunk info : " + info.toString());
+        throw new StorageContainerException("Not Supported Operation. " +
+            "Trying to delete a chunk that is in shared file. chunk info : "
+            + info.toString(), UNSUPPORTED_REQUEST);
       }
     } finally {
       containerManager.readUnlock();

http://git-wip-us.apache.org/repos/asf/hadoop/blob/40741236/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/ContainerManagerImpl.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/ContainerManagerImpl.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/ContainerManagerImpl.java
index 816032e..1b45332 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/ContainerManagerImpl.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/ContainerManagerImpl.java
@@ -22,8 +22,8 @@ import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Preconditions;
 import org.apache.commons.codec.digest.DigestUtils;
 import org.apache.hadoop.conf.Configuration;
-import org.apache.hadoop.fs.FileAlreadyExistsException;
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos;
+import org.apache.hadoop.scm.container.common.helpers.StorageContainerException;
 import org.apache.hadoop.ozone.protocol.proto
     .StorageContainerDatanodeProtocolProtos.SCMNodeReport;
 import org.apache.hadoop.ozone.protocol.proto
@@ -60,6 +60,20 @@ import java.util.concurrent.ConcurrentSkipListMap;
 import java.util.concurrent.locks.ReentrantReadWriteLock;
 
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_DATANODE_DATA_DIR_KEY;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.CONTAINER_EXISTS;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.CONTAINER_INTERNAL_ERROR;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.CONTAINER_NOT_FOUND;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.INVALID_CONFIG;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.IO_EXCEPTION;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.NO_SUCH_ALGORITHM;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.UNABLE_TO_READ_METADATA_DB;
 import static org.apache.hadoop.ozone.OzoneConsts.CONTAINER_EXTENSION;
 import static org.apache.hadoop.ozone.OzoneConsts.CONTAINER_META;
 
@@ -85,7 +99,7 @@ public class ContainerManagerImpl implements ContainerManager {
   /**
    * Init call that sets up a container Manager.
    *
-   * @param config        - Configuration.
+   * @param config - Configuration.
    * @param containerDirs - List of Metadata Container locations.
    * @throws IOException
    */
@@ -93,26 +107,32 @@ public class ContainerManagerImpl implements ContainerManager {
   public void init(
       Configuration config, List<StorageLocation> containerDirs)
       throws IOException {
-    Preconditions.checkNotNull(config);
-    Preconditions.checkNotNull(containerDirs);
-    Preconditions.checkState(containerDirs.size() > 0);
+    Preconditions.checkNotNull(config, "Config must not be null");
+    Preconditions.checkNotNull(containerDirs, "Container directories cannot " +
+        "be null");
+    Preconditions.checkState(containerDirs.size() > 0, "Number of container" +
+        " directories must be greater than zero.");
 
     readLock();
     try {
       for (StorageLocation path : containerDirs) {
         File directory = Paths.get(path.getNormalizedUri()).toFile();
+        // TODO: This will fail if any directory is invalid.
+        // We should fix this to handle invalid directories and continue.
+        // Leaving it this way to fail fast for time being.
         if (!directory.isDirectory()) {
           LOG.error("Invalid path to container metadata directory. path: {}",
               path.toString());
-          throw new IOException("Invalid path to container metadata directory" +
-              ". " + path);
+          throw new StorageContainerException("Invalid path to container " +
+              "metadata directory." + path, INVALID_CONFIG);
         }
         File[] files = directory.listFiles(new ContainerFilter());
         if (files != null) {
           for (File containerFile : files) {
             String containerPath =
                 ContainerUtils.getContainerNameFromFile(containerFile);
-            Preconditions.checkNotNull(containerPath);
+            Preconditions.checkNotNull(containerPath, "Container path cannot" +
+                " be null");
             readContainerInfo(containerPath);
           }
         }
@@ -136,10 +156,12 @@ public class ContainerManagerImpl implements ContainerManager {
    * the checksums match, then that file is added to containerMap.
    *
    * @param containerName - Name which points to the persisted container.
+   * @throws StorageContainerException
    */
   private void readContainerInfo(String containerName)
-      throws IOException {
-    Preconditions.checkState(containerName.length() > 0);
+      throws StorageContainerException {
+    Preconditions.checkState(containerName.length() > 0,
+        "Container name length cannot be zero.");
     FileInputStream containerStream = null;
     DigestInputStream dis = null;
     FileInputStream metaStream = null;
@@ -148,7 +170,8 @@ public class ContainerManagerImpl implements ContainerManager {
     if (cPath != null) {
       keyName = cPath.toString();
     }
-    Preconditions.checkNotNull(keyName);
+    Preconditions.checkNotNull(keyName,
+        "Container Name  to container key mapping is null");
 
     try {
       String containerFileName = containerName.concat(CONTAINER_EXTENSION);
@@ -169,21 +192,31 @@ public class ContainerManagerImpl implements ContainerManager {
       ContainerProtos.ContainerMeta meta = ContainerProtos.ContainerMeta
           .parseDelimitedFrom(metaStream);
 
-      if (meta != null && !DigestUtils.sha256Hex(sha.digest()).equals(meta
-          .getHash())) {
-        throw new IOException("Invalid SHA found for file.");
+      if (meta != null &&
+          !DigestUtils.sha256Hex(sha.digest()).equals(meta.getHash())) {
+        // This means we were not able read data from the disk when booted the
+        // datanode. We are going to rely on SCM understanding that we don't
+        // have
+        // valid data for this container when we send container reports.
+        // Hopefully SCM will ask us to delete this container and rebuild it.
+        LOG.error("Invalid SHA found for container data. Name :{}" +
+            "cowardly refusing to read invalid data", containerName);
+        containerMap.put(keyName, new ContainerStatus(null, false));
+        return;
       }
 
       containerMap.put(keyName, new ContainerStatus(containerData, true));
 
     } catch (IOException | NoSuchAlgorithmException ex) {
-      LOG.error("read failed for file: {} ex: {}",
-          containerName, ex.getMessage());
+      LOG.error("read failed for file: {} ex: {}", containerName,
+          ex.getMessage());
 
       // TODO : Add this file to a recovery Queue.
 
       // Remember that this container is busted and we cannot use it.
       containerMap.put(keyName, new ContainerStatus(null, false));
+      throw new StorageContainerException("Unable to read container info",
+          UNABLE_TO_READ_METADATA_DB);
     } finally {
       IOUtils.closeStream(dis);
       IOUtils.closeStream(containerStream);
@@ -194,19 +227,20 @@ public class ContainerManagerImpl implements ContainerManager {
   /**
    * Creates a container with the given name.
    *
-   * @param pipeline      -- Nodes which make up this container.
+   * @param pipeline -- Nodes which make up this container.
    * @param containerData - Container Name and metadata.
-   * @throws IOException
+   * @throws StorageContainerException - Exception
    */
   @Override
   public void createContainer(Pipeline pipeline, ContainerData containerData)
-      throws IOException {
-    Preconditions.checkNotNull(containerData);
-
+      throws StorageContainerException {
+    Preconditions.checkNotNull(containerData, "Container data cannot be null");
     writeLock();
     try {
       if (containerMap.containsKey(containerData.getName())) {
-        throw new FileAlreadyExistsException("container already exists.");
+        LOG.debug("container already exists. {}", containerData.getName());
+        throw new StorageContainerException("container already exists.",
+            CONTAINER_EXISTS);
       }
 
       // This is by design. We first write and close the
@@ -218,8 +252,10 @@ public class ContainerManagerImpl implements ContainerManager {
       File cFile = new File(containerData.getContainerPath());
       readContainerInfo(ContainerUtils.getContainerNameFromFile(cFile));
     } catch (NoSuchAlgorithmException ex) {
-      throw new IOException("failed to create container", ex);
-
+      LOG.error("Internal error: We seem to be running a JVM without a " +
+          "needed hash algorithm.");
+      throw new StorageContainerException("failed to create container",
+          NO_SUCH_ALGORITHM);
     } finally {
       writeUnlock();
     }
@@ -244,22 +280,25 @@ public class ContainerManagerImpl implements ContainerManager {
    * }
    *
    * @param containerData - container Data
+   * @throws StorageContainerException, NoSuchAlgorithmException
    */
   private void writeContainerInfo(ContainerData containerData)
-      throws IOException, NoSuchAlgorithmException {
+      throws StorageContainerException, NoSuchAlgorithmException {
 
-    Preconditions.checkNotNull(this.locationManager);
+    Preconditions.checkNotNull(this.locationManager,
+        "Internal error: location manager cannot be null");
 
     FileOutputStream containerStream = null;
     DigestOutputStream dos = null;
     FileOutputStream metaStream = null;
-    Path location = locationManager.getContainerPath();
-
-    File containerFile = ContainerUtils.getContainerFile(containerData,
-        location);
-    File metadataFile = ContainerUtils.getMetadataFile(containerData, location);
 
     try {
+      Path location = locationManager.getContainerPath();
+      File containerFile = ContainerUtils.getContainerFile(containerData,
+          location);
+      File metadataFile = ContainerUtils.getMetadataFile(containerData,
+          location);
+
       ContainerUtils.verifyIsNewContainer(containerFile, metadataFile);
 
       Path metadataPath = this.locationManager.getDataPath(
@@ -287,7 +326,6 @@ public class ContainerManagerImpl implements ContainerManager {
       protoMeta.writeDelimitedTo(metaStream);
 
     } catch (IOException ex) {
-
       // TODO : we need to clean up partially constructed files
       // The proper way to do would be for a thread
       // to read all these 3 artifacts and make sure they are
@@ -296,10 +334,15 @@ public class ContainerManagerImpl implements ContainerManager {
 
       // In case of ozone this is *not* a deal breaker since
       // SCM is guaranteed to generate unique container names.
-
-      LOG.error("creation of container failed. Name: {} ",
-          containerData.getContainerName());
-      throw ex;
+      // The saving grace is that we check if we have residue files
+      // lying around when creating a new container. We need to queue
+      // this information to a cleaner thread.
+
+      LOG.error("Creation of container failed. Name: {}, we might need to " +
+              "cleanup partially created artifacts. ",
+          containerData.getContainerName(), ex);
+      throw new StorageContainerException("Container creation failed. ",
+          ex, CONTAINER_INTERNAL_ERROR);
     } finally {
       IOUtils.closeStream(dos);
       IOUtils.closeStream(containerStream);
@@ -307,32 +350,37 @@ public class ContainerManagerImpl implements ContainerManager {
     }
   }
 
-
-
   /**
    * Deletes an existing container.
    *
-   * @param pipeline      - nodes that make this container.
+   * @param pipeline - nodes that make this container.
    * @param containerName - name of the container.
-   * @throws IOException
+   * @throws StorageContainerException
    */
   @Override
   public void deleteContainer(Pipeline pipeline, String containerName) throws
-      IOException {
-    Preconditions.checkState(containerName.length() > 0);
+      StorageContainerException {
+    Preconditions.checkNotNull(containerName, "Container name cannot be null");
+    Preconditions.checkState(containerName.length() > 0,
+        "Container name length cannot be zero.");
     writeLock();
     try {
       ContainerStatus status = containerMap.get(containerName);
       if (status == null) {
-        LOG.info("No such container. Name: {}", containerName);
-        throw new IOException("No such container. Name : " + containerName);
+        LOG.debug("No such container. Name: {}", containerName);
+        throw new StorageContainerException("No such container. Name : " +
+            containerName, CONTAINER_NOT_FOUND);
       }
       ContainerUtils.removeContainer(status.containerData);
       containerMap.remove(containerName);
+    } catch (IOException e) {
+      // TODO : An I/O error during delete can leave partial artifacts on the
+      // disk. We will need the cleaner thread to cleanup this information.
+      LOG.error("Failed to cleanup container. Name: {}", containerName, e);
+      throw new StorageContainerException(containerName, e, IO_EXCEPTION);
     } finally {
       writeUnlock();
     }
-
   }
 
   /**
@@ -343,20 +391,21 @@ public class ContainerManagerImpl implements ContainerManager {
    * time. It is possible that using this iteration you can miss certain
    * container from the listing.
    *
-   * @param prefix  -  Return keys that match this prefix.
-   * @param count   - how many to return
+   * @param prefix -  Return keys that match this prefix.
+   * @param count - how many to return
    * @param prevKey - Previous Key Value or empty String.
-   * @param data    - Actual containerData
-   * @throws IOException
+   * @param data - Actual containerData
+   * @throws StorageContainerException
    */
   @Override
   public void listContainer(String prefix, long count, String prevKey,
-                            List<ContainerData> data) throws IOException {
+      List<ContainerData> data) throws StorageContainerException {
     // TODO : Support list with Prefix and PrevKey
-    Preconditions.checkNotNull(data);
+    Preconditions.checkNotNull(data,
+        "Internal assertion: data cannot be null");
     readLock();
     try {
-      ConcurrentNavigableMap<String, ContainerStatus> map = null;
+      ConcurrentNavigableMap<String, ContainerStatus> map;
       if (prevKey == null || prevKey.isEmpty()) {
         map = containerMap.tailMap(containerMap.firstKey(), true);
       } else {
@@ -382,13 +431,17 @@ public class ContainerManagerImpl implements ContainerManager {
    *
    * @param containerName - Name of the container
    * @return ContainerData - Container Data.
-   * @throws IOException
+   * @throws StorageContainerException
    */
   @Override
-  public ContainerData readContainer(String containerName) throws IOException {
-    if(!containerMap.containsKey(containerName)) {
-      throw new IOException("Unable to find the container. Name: "
-          + containerName);
+  public ContainerData readContainer(String containerName) throws
+      StorageContainerException {
+    Preconditions.checkNotNull(containerName, "Container name cannot be null");
+    Preconditions.checkState(containerName.length() > 0,
+        "Container name length cannot be zero.");
+    if (!containerMap.containsKey(containerName)) {
+      throw new StorageContainerException("Unable to find the container. Name: "
+          + containerName, CONTAINER_NOT_FOUND);
     }
     return containerMap.get(containerName).getContainer();
   }
@@ -400,7 +453,8 @@ public class ContainerManagerImpl implements ContainerManager {
    */
   @Override
   public void shutdown() throws IOException {
-    Preconditions.checkState(this.hasWriteLock());
+    Preconditions.checkState(this.hasWriteLock(),
+        "Assumption that we are holding the lock violated.");
     this.containerMap.clear();
     this.locationManager.shutdown();
   }
@@ -470,26 +524,17 @@ public class ContainerManagerImpl implements ContainerManager {
     return this.lock.writeLock().isHeldByCurrentThread();
   }
 
-  /**
-   * Sets the chunk Manager.
-   * @param chunkManager
-   */
-  public void setChunkManager(ChunkManager chunkManager) {
-    this.chunkManager = chunkManager;
-  }
-
   public ChunkManager getChunkManager() {
     return this.chunkManager;
   }
 
   /**
-   * Sets the Key Manager.
+   * Sets the chunk Manager.
    *
-   * @param keyManager - Key Manager.
+   * @param chunkManager - Chunk Manager
    */
-  @Override
-  public void setKeyManager(KeyManager keyManager) {
-    this.keyManager = keyManager;
+  public void setChunkManager(ChunkManager chunkManager) {
+    this.chunkManager = chunkManager;
   }
 
   /**
@@ -522,13 +567,23 @@ public class ContainerManagerImpl implements ContainerManager {
   }
 
   /**
+   * Sets the Key Manager.
+   *
+   * @param keyManager - Key Manager.
+   */
+  @Override
+  public void setKeyManager(KeyManager keyManager) {
+    this.keyManager = keyManager;
+  }
+
+  /**
    * Filter out only container files from the container metadata dir.
    */
   private static class ContainerFilter implements FilenameFilter {
     /**
      * Tests if a specified file should be included in a file list.
      *
-     * @param dir  the directory in which the file was found.
+     * @param dir the directory in which the file was found.
      * @param name the name of the file.
      * @return <code>true</code> if and only if the name should be included in
      * the file list; <code>false</code> otherwise.
@@ -557,7 +612,7 @@ public class ContainerManagerImpl implements ContainerManager {
      * Creates a Container Status class.
      *
      * @param containerData - ContainerData.
-     * @param active        - Active or not active.
+     * @param active - Active or not active.
      */
     ContainerStatus(ContainerData containerData, boolean active) {
       this.containerData = containerData;
@@ -580,7 +635,7 @@ public class ContainerManagerImpl implements ContainerManager {
     /**
      * Indicates if a container is Active.
      *
-     * @return
+     * @return true if it is active.
      */
     public boolean isActive() {
       return active;

http://git-wip-us.apache.org/repos/asf/hadoop/blob/40741236/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/Dispatcher.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/Dispatcher.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/Dispatcher.java
index 8cdbf9a..510ed3c 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/Dispatcher.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/Dispatcher.java
@@ -30,14 +30,15 @@ import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos.Type;
 import org.apache.hadoop.ozone.container.common.helpers.ChunkInfo;
 import org.apache.hadoop.ozone.container.common.helpers.ChunkUtils;
 import org.apache.hadoop.ozone.container.common.helpers.ContainerData;
+import org.apache.hadoop.ozone.container.common.helpers.ContainerMetrics;
 import org.apache.hadoop.ozone.container.common.helpers.ContainerUtils;
 import org.apache.hadoop.ozone.container.common.helpers.FileUtils;
 import org.apache.hadoop.ozone.container.common.helpers.KeyData;
 import org.apache.hadoop.ozone.container.common.helpers.KeyUtils;
-import org.apache.hadoop.ozone.container.common.helpers.ContainerMetrics;
 import org.apache.hadoop.ozone.container.common.interfaces.ContainerDispatcher;
 import org.apache.hadoop.ozone.container.common.interfaces.ContainerManager;
 import org.apache.hadoop.scm.container.common.helpers.Pipeline;
+import org.apache.hadoop.scm.container.common.helpers.StorageContainerException;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -45,6 +46,11 @@ import java.io.IOException;
 import java.util.LinkedList;
 import java.util.List;
 
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.PUT_SMALL_FILE_ERROR;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.GET_SMALL_FILE_ERROR;
+
 /**
  * Ozone Container dispatcher takes a call from the netty server and routes it
  * to the right handler function.
@@ -55,6 +61,7 @@ public class Dispatcher implements ContainerDispatcher {
   private final ContainerManager containerManager;
   private ContainerMetrics metrics;
   private Configuration conf;
+
   /**
    * Constructs an OzoneContainer that receives calls from
    * XceiverServerHandler.
@@ -79,59 +86,67 @@ public class Dispatcher implements ContainerDispatcher {
 
   @Override
   public ContainerCommandResponseProto dispatch(
-      ContainerCommandRequestProto msg) throws IOException {
+      ContainerCommandRequestProto msg) {
     long startNanos = System.nanoTime();
     ContainerCommandResponseProto resp = null;
-    Preconditions.checkNotNull(msg);
-    Type cmdType = msg.getCmdType();
-    metrics.incContainerOpcMetrics(cmdType);
-    if ((cmdType == Type.CreateContainer) ||
-        (cmdType == Type.DeleteContainer) ||
-        (cmdType == Type.ReadContainer) ||
-        (cmdType == Type.ListContainer) ||
-        (cmdType == Type.UpdateContainer)) {
-      resp = containerProcessHandler(msg);
-    }
+    try {
+      Preconditions.checkNotNull(msg);
+      Type cmdType = msg.getCmdType();
+      metrics.incContainerOpcMetrics(cmdType);
+      if ((cmdType == Type.CreateContainer) ||
+          (cmdType == Type.DeleteContainer) ||
+          (cmdType == Type.ReadContainer) ||
+          (cmdType == Type.ListContainer) ||
+          (cmdType == Type.UpdateContainer)) {
+        resp = containerProcessHandler(msg);
+      }
 
-    if ((cmdType == Type.PutKey) ||
-        (cmdType == Type.GetKey) ||
-        (cmdType == Type.DeleteKey) ||
-        (cmdType == Type.ListKey)) {
-      resp = keyProcessHandler(msg);
-    }
+      if ((cmdType == Type.PutKey) ||
+          (cmdType == Type.GetKey) ||
+          (cmdType == Type.DeleteKey) ||
+          (cmdType == Type.ListKey)) {
+        resp = keyProcessHandler(msg);
+      }
 
-    if ((cmdType == Type.WriteChunk) ||
-        (cmdType == Type.ReadChunk) ||
-        (cmdType == Type.DeleteChunk)) {
-      resp = chunkProcessHandler(msg);
-    }
+      if ((cmdType == Type.WriteChunk) ||
+          (cmdType == Type.ReadChunk) ||
+          (cmdType == Type.DeleteChunk)) {
+        resp = chunkProcessHandler(msg);
+      }
 
-    if ((cmdType == Type.PutSmallFile) ||
-        (cmdType == Type.GetSmallFile)) {
-      resp = smallFileHandler(msg);
-    }
+      if ((cmdType == Type.PutSmallFile) ||
+          (cmdType == Type.GetSmallFile)) {
+        resp = smallFileHandler(msg);
+      }
 
-    if (resp != null) {
-      metrics.incContainerOpsLatencies(cmdType,
-                            System.nanoTime() - startNanos);
-      return resp;
-    }
+      if (resp != null) {
+        metrics.incContainerOpsLatencies(cmdType,
+            System.nanoTime() - startNanos);
+        return resp;
+      }
 
-    return ContainerUtils.unsupportedRequest(msg);
+      return ContainerUtils.unsupportedRequest(msg);
+    } catch (StorageContainerException e) {
+      // This useful since the trace ID will allow us to correlate failures.
+      return ContainerUtils.logAndReturnError(LOG, e, msg);
+    } catch (IllegalStateException | NullPointerException e) {
+      return ContainerUtils.logAndReturnError(LOG, e, msg);
+    }
   }
 
   public ContainerMetrics getContainerMetrics() {
     return metrics;
   }
+
   /**
    * Handles the all Container related functionality.
    *
    * @param msg - command
    * @return - response
-   * @throws IOException
+   * @throws StorageContainerException
    */
   private ContainerCommandResponseProto containerProcessHandler(
-      ContainerCommandRequestProto msg) throws IOException {
+      ContainerCommandRequestProto msg) throws StorageContainerException {
     try {
 
       switch (msg.getCmdType()) {
@@ -175,10 +190,10 @@ public class Dispatcher implements ContainerDispatcher {
    *
    * @param msg - command
    * @return - response
-   * @throws IOException
+   * @throws StorageContainerException
    */
   private ContainerCommandResponseProto keyProcessHandler(
-      ContainerCommandRequestProto msg) throws IOException {
+      ContainerCommandRequestProto msg) throws StorageContainerException {
     try {
       switch (msg.getCmdType()) {
       case PutKey:
@@ -217,10 +232,10 @@ public class Dispatcher implements ContainerDispatcher {
    *
    * @param msg - command
    * @return - response
-   * @throws IOException
+   * @throws StorageContainerException
    */
   private ContainerCommandResponseProto chunkProcessHandler(
-      ContainerCommandRequestProto msg) throws IOException {
+      ContainerCommandRequestProto msg) throws StorageContainerException {
     try {
       switch (msg.getCmdType()) {
       case WriteChunk:
@@ -254,7 +269,7 @@ public class Dispatcher implements ContainerDispatcher {
   }
 
   private ContainerCommandResponseProto smallFileHandler(
-      ContainerCommandRequestProto msg) throws IOException {
+      ContainerCommandRequestProto msg) throws StorageContainerException {
     switch (msg.getCmdType()) {
     case PutSmallFile:
       return handlePutSmallFile(msg);
@@ -494,7 +509,6 @@ public class Dispatcher implements ContainerDispatcher {
     String keyName = msg.getDeleteKey().getName();
     Preconditions.checkNotNull(keyName);
     Preconditions.checkState(!keyName.isEmpty());
-
     this.containerManager.getKeyManager().deleteKey(pipeline, keyName);
     return KeyUtils.getKeyResponse(msg);
   }
@@ -504,34 +518,41 @@ public class Dispatcher implements ContainerDispatcher {
    *
    * @param msg - Message.
    * @return ContainerCommandResponseProto
-   * @throws IOException
+   * @throws StorageContainerException
    */
   private ContainerCommandResponseProto handlePutSmallFile(
-      ContainerCommandRequestProto msg) throws IOException {
+      ContainerCommandRequestProto msg) throws StorageContainerException {
 
     if (!msg.hasPutSmallFile()) {
       LOG.debug("Malformed put small file request. trace ID: {}",
           msg.getTraceID());
       return ContainerUtils.malformedRequest(msg);
     }
+    try {
 
-    Pipeline pipeline =
-        Pipeline.getFromProtoBuf(msg.getPutSmallFile().getKey().getPipeline());
-    Preconditions.checkNotNull(pipeline);
-    KeyData keyData = KeyData.getFromProtoBuf(msg.getPutSmallFile().getKey()
-        .getKeyData());
-    ChunkInfo chunkInfo = ChunkInfo.getFromProtoBuf(msg.getPutSmallFile()
-        .getChunkInfo());
-    byte[] data = msg.getPutSmallFile().getData().toByteArray();
-
-    metrics.incContainerBytesStats(Type.PutSmallFile, data.length);
-    this.containerManager.getChunkManager().writeChunk(pipeline, keyData
-        .getKeyName(), chunkInfo, data);
-    List<ContainerProtos.ChunkInfo> chunks = new LinkedList<>();
-    chunks.add(chunkInfo.getProtoBufMessage());
-    keyData.setChunks(chunks);
-    this.containerManager.getKeyManager().putKey(pipeline, keyData);
-    return FileUtils.getPutFileResponse(msg);
+      Pipeline pipeline =
+          Pipeline.getFromProtoBuf(msg.getPutSmallFile()
+              .getKey().getPipeline());
+
+      Preconditions.checkNotNull(pipeline);
+      KeyData keyData = KeyData.getFromProtoBuf(msg.getPutSmallFile().getKey()
+          .getKeyData());
+      ChunkInfo chunkInfo = ChunkInfo.getFromProtoBuf(msg.getPutSmallFile()
+          .getChunkInfo());
+      byte[] data = msg.getPutSmallFile().getData().toByteArray();
+
+      metrics.incContainerBytesStats(Type.PutSmallFile, data.length);
+      this.containerManager.getChunkManager().writeChunk(pipeline, keyData
+          .getKeyName(), chunkInfo, data);
+      List<ContainerProtos.ChunkInfo> chunks = new LinkedList<>();
+      chunks.add(chunkInfo.getProtoBufMessage());
+      keyData.setChunks(chunks);
+      this.containerManager.getKeyManager().putKey(pipeline, keyData);
+      return FileUtils.getPutFileResponse(msg);
+    } catch (IOException e) {
+      throw new StorageContainerException("Put Small File Failed.", e,
+          PUT_SMALL_FILE_ERROR);
+    }
   }
 
   /**
@@ -540,35 +561,44 @@ public class Dispatcher implements ContainerDispatcher {
    *
    * @param msg - ContainerCommandRequestProto
    * @return ContainerCommandResponseProto
+   * @throws StorageContainerException
    */
   private ContainerCommandResponseProto handleGetSmallFile(
-      ContainerCommandRequestProto msg) throws IOException {
+      ContainerCommandRequestProto msg) throws StorageContainerException {
     ByteString dataBuf = ByteString.EMPTY;
     if (!msg.hasGetSmallFile()) {
       LOG.debug("Malformed get small file request. trace ID: {}",
           msg.getTraceID());
       return ContainerUtils.malformedRequest(msg);
     }
-    Pipeline pipeline =
-        Pipeline.getFromProtoBuf(msg.getGetSmallFile().getKey().getPipeline());
-    long bytes = 0;
-    Preconditions.checkNotNull(pipeline);
-    KeyData keyData = KeyData.getFromProtoBuf(msg.getGetSmallFile()
-        .getKey().getKeyData());
-    KeyData data = this.containerManager.getKeyManager().getKey(keyData);
-    ContainerProtos.ChunkInfo c = null;
-    for (ContainerProtos.ChunkInfo chunk : data.getChunks()) {
-      bytes += chunk.getSerializedSize();
-      ByteString current =
-          ByteString.copyFrom(this.containerManager.getChunkManager().readChunk(
-              pipeline, keyData.getKeyName(), ChunkInfo.getFromProtoBuf(
-                  chunk)));
-      dataBuf = dataBuf.concat(current);
-      c = chunk;
+    try {
+      Pipeline pipeline =
+          Pipeline.getFromProtoBuf(msg.getGetSmallFile()
+              .getKey().getPipeline());
+
+      long bytes = 0;
+      Preconditions.checkNotNull(pipeline);
+      KeyData keyData = KeyData.getFromProtoBuf(msg.getGetSmallFile()
+          .getKey().getKeyData());
+      KeyData data = this.containerManager.getKeyManager().getKey(keyData);
+      ContainerProtos.ChunkInfo c = null;
+      for (ContainerProtos.ChunkInfo chunk : data.getChunks()) {
+        bytes += chunk.getSerializedSize();
+        ByteString current =
+            ByteString.copyFrom(this.containerManager.getChunkManager()
+                .readChunk(
+                    pipeline, keyData.getKeyName(), ChunkInfo.getFromProtoBuf(
+                        chunk)));
+        dataBuf = dataBuf.concat(current);
+        c = chunk;
+      }
+      metrics.incContainerBytesStats(Type.GetSmallFile, bytes);
+      return FileUtils.getGetSmallFileResponse(msg, dataBuf.toByteArray(),
+          ChunkInfo.getFromProtoBuf(c));
+    } catch (IOException e) {
+      throw new StorageContainerException("Unable to decode protobuf", e,
+          GET_SMALL_FILE_ERROR);
+
     }
-    metrics.incContainerBytesStats(Type.GetSmallFile,  bytes);
-    return FileUtils.getGetSmallFileResponse(msg, dataBuf.toByteArray(),
-        ChunkInfo.getFromProtoBuf(c));
   }
-
 }

http://git-wip-us.apache.org/repos/asf/hadoop/blob/40741236/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/KeyManagerImpl.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/KeyManagerImpl.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/KeyManagerImpl.java
index 7757958..1a0bd78 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/KeyManagerImpl.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/impl/KeyManagerImpl.java
@@ -25,19 +25,31 @@ import org.apache.hadoop.ozone.OzoneConfigKeys;
 import org.apache.hadoop.ozone.container.common.helpers.ContainerData;
 import org.apache.hadoop.ozone.container.common.helpers.KeyData;
 import org.apache.hadoop.ozone.container.common.helpers.KeyUtils;
-import org.apache.hadoop.scm.container.common.helpers.Pipeline;
 import org.apache.hadoop.ozone.container.common.interfaces.ContainerManager;
 import org.apache.hadoop.ozone.container.common.interfaces.KeyManager;
 import org.apache.hadoop.ozone.container.common.utils.ContainerCache;
+import org.apache.hadoop.scm.container.common.helpers.Pipeline;
+import org.apache.hadoop.scm.container.common.helpers.StorageContainerException;
 import org.apache.hadoop.utils.LevelDBStore;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
 import java.util.List;
 
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.IO_EXCEPTION;
+import static org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos
+    .Result.NO_SUCH_KEY;
+
+
 /**
  * Key Manager impl.
  */
 public class KeyManagerImpl implements KeyManager {
+  static final Logger LOG =
+      LoggerFactory.getLogger(KeyManagerImpl.class);
+
   private static final float LOAD_FACTOR = 0.75f;
   private final ContainerManager containerManager;
   private final ContainerCache containerCache;
@@ -48,8 +60,9 @@ public class KeyManagerImpl implements KeyManager {
    * @param containerManager - Container Manager.
    */
   public KeyManagerImpl(ContainerManager containerManager, Configuration conf) {
-    Preconditions.checkNotNull(containerManager);
-    Preconditions.checkNotNull(conf);
+    Preconditions.checkNotNull(containerManager, "Container manager cannot be" +
+        " null");
+    Preconditions.checkNotNull(conf, "Config cannot be null");
     int cacheSize = conf.getInt(OzoneConfigKeys.OZONE_KEY_CACHE,
         OzoneConfigKeys.OZONE_KEY_CACHE_DEFAULT);
     this.containerManager = containerManager;
@@ -60,17 +73,22 @@ public class KeyManagerImpl implements KeyManager {
    * {@inheritDoc}
    */
   @Override
-  public void putKey(Pipeline pipeline, KeyData data) throws IOException {
+  public void putKey(Pipeline pipeline, KeyData data)
+      throws StorageContainerException {
     containerManager.readLock();
     try {
       // We are not locking the key manager since LevelDb serializes all actions
       // against a single DB. We rely on DB level locking to avoid conflicts.
-      Preconditions.checkNotNull(pipeline);
-      Preconditions.checkNotNull(pipeline.getContainerName());
+      Preconditions.checkNotNull(pipeline, "Pipeline cannot be null");
+      Preconditions.checkNotNull(pipeline.getContainerName(),
+          "Container name cannot be null");
       ContainerData cData = containerManager.readContainer(
           pipeline.getContainerName());
       LevelDBStore db = KeyUtils.getDB(cData, containerCache);
-      Preconditions.checkNotNull(db);
+
+      // This is a post condition that acts as a hint to the user.
+      // Should never fail.
+      Preconditions.checkNotNull(db, "DB cannot be null here");
       db.put(data.getKeyName().getBytes(KeyUtils.ENCODING), data
           .getProtoBufMessage().toByteArray());
     } finally {
@@ -83,22 +101,30 @@ public class KeyManagerImpl implements KeyManager {
    * {@inheritDoc}
    */
   @Override
-  public KeyData getKey(KeyData data) throws IOException {
+  public KeyData getKey(KeyData data) throws StorageContainerException {
     containerManager.readLock();
     try {
-      Preconditions.checkNotNull(data);
-      Preconditions.checkNotNull(data.getContainerName());
+      Preconditions.checkNotNull(data, "Key data cannot be null");
+      Preconditions.checkNotNull(data.getContainerName(),
+          "Container name cannot be null");
       ContainerData cData = containerManager.readContainer(data
           .getContainerName());
       LevelDBStore db = KeyUtils.getDB(cData, containerCache);
-      Preconditions.checkNotNull(db);
+
+      // This is a post condition that acts as a hint to the user.
+      // Should never fail.
+      Preconditions.checkNotNull(db, "DB cannot be null here");
+
       byte[] kData = db.get(data.getKeyName().getBytes(KeyUtils.ENCODING));
-      if(kData == null) {
-        throw new IOException("Unable to find the key.");
+      if (kData == null) {
+        throw new StorageContainerException("Unable to find the key.",
+            NO_SUCH_KEY);
       }
       ContainerProtos.KeyData keyData =
           ContainerProtos.KeyData.parseFrom(kData);
       return KeyData.getFromProtoBuf(keyData);
+    } catch (IOException ex) {
+      throw new StorageContainerException(ex, IO_EXCEPTION);
     } finally {
       containerManager.readUnlock();
     }
@@ -108,24 +134,29 @@ public class KeyManagerImpl implements KeyManager {
    * {@inheritDoc}
    */
   @Override
-  public void deleteKey(Pipeline pipeline, String keyName) throws IOException {
+  public void deleteKey(Pipeline pipeline, String keyName)
+      throws StorageContainerException {
     containerManager.readLock();
     try {
-      Preconditions.checkNotNull(pipeline);
-      Preconditions.checkNotNull(pipeline.getContainerName());
+      Preconditions.checkNotNull(pipeline, "Pipeline cannot be null");
+      Preconditions.checkNotNull(pipeline.getContainerName(),
+          "Container name cannot be null");
       ContainerData cData = containerManager.readContainer(pipeline
           .getContainerName());
       LevelDBStore db = KeyUtils.getDB(cData, containerCache);
-      Preconditions.checkNotNull(db);
 
+      // This is a post condition that acts as a hint to the user.
+      // Should never fail.
+      Preconditions.checkNotNull(db, "DB cannot be null here");
       // Note : There is a race condition here, since get and delete
       // are not atomic. Leaving it here since the impact is refusing
       // to delete a key which might have just gotten inserted after
       // the get check.
 
       byte[] kData = db.get(keyName.getBytes(KeyUtils.ENCODING));
-      if(kData == null) {
-        throw new IOException("Unable to find the key.");
+      if (kData == null) {
+        throw new StorageContainerException("Unable to find the key.",
+            NO_SUCH_KEY);
       }
       db.delete(keyName.getBytes(KeyUtils.ENCODING));
     } finally {
@@ -139,7 +170,7 @@ public class KeyManagerImpl implements KeyManager {
   @Override
   public List<KeyData> listKey(Pipeline pipeline, String prefix, String
       prevKey, int count) {
-    // TODO :
+    // TODO : Implement listKey function.
     return null;
   }
 
@@ -148,7 +179,8 @@ public class KeyManagerImpl implements KeyManager {
    */
   @Override
   public void shutdown() {
-    Preconditions.checkState(this.containerManager.hasWriteLock());
+    Preconditions.checkState(this.containerManager.hasWriteLock(), "asserts " +
+        "that we are holding the container manager lock when shutting down.");
     KeyUtils.shutdownCache(containerCache);
   }
 }

http://git-wip-us.apache.org/repos/asf/hadoop/blob/40741236/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/interfaces/ChunkManager.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/interfaces/ChunkManager.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/interfaces/ChunkManager.java
index 7adcd56..8e309d9 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/interfaces/ChunkManager.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/interfaces/ChunkManager.java
@@ -18,11 +18,10 @@
 
 package org.apache.hadoop.ozone.container.common.interfaces;
 
+import org.apache.hadoop.scm.container.common.helpers.StorageContainerException;
 import org.apache.hadoop.ozone.container.common.helpers.ChunkInfo;
 import org.apache.hadoop.scm.container.common.helpers.Pipeline;
 
-import java.io.IOException;
-
 /**
  * Chunk Manager allows read, write, delete and listing of chunks in
  * a container.
@@ -34,10 +33,10 @@ public interface ChunkManager {
    * @param pipeline - Name and the set of machines that make this container.
    * @param keyName - Name of the Key.
    * @param info - ChunkInfo.
-   * @throws IOException
+   * @throws StorageContainerException
    */
   void writeChunk(Pipeline pipeline, String keyName,
-                  ChunkInfo info, byte[] data) throws IOException;
+                  ChunkInfo info, byte[] data) throws StorageContainerException;
 
   /**
    * reads the data defined by a chunk.
@@ -45,23 +44,23 @@ public interface ChunkManager {
    * @param keyName - Name of the Key
    * @param info - ChunkInfo.
    * @return  byte array
-   * @throws IOException
+   * @throws StorageContainerException
    *
    * TODO: Right now we do not support partial reads and writes of chunks.
    * TODO: Explore if we need to do that for ozone.
    */
   byte[] readChunk(Pipeline pipeline, String keyName, ChunkInfo info) throws
-      IOException;
+      StorageContainerException;
 
   /**
    * Deletes a given chunk.
    * @param pipeline  - Pipeline.
    * @param keyName   - Key Name
    * @param info  - Chunk Info
-   * @throws IOException
+   * @throws StorageContainerException
    */
   void deleteChunk(Pipeline pipeline, String keyName, ChunkInfo info) throws
-      IOException;
+      StorageContainerException;
 
   // TODO : Support list operations.
 

http://git-wip-us.apache.org/repos/asf/hadoop/blob/40741236/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/interfaces/ContainerDispatcher.java
----------------------------------------------------------------------
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/interfaces/ContainerDispatcher.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/interfaces/ContainerDispatcher.java
index 48ca5de..8aae004 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/interfaces/ContainerDispatcher.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/ozone/container/common/interfaces/ContainerDispatcher.java
@@ -21,8 +21,6 @@ package org.apache.hadoop.ozone.container.common.interfaces;
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos.ContainerCommandResponseProto;
 import org.apache.hadoop.hdfs.ozone.protocol.proto.ContainerProtos.ContainerCommandRequestProto;
 
-import java.io.IOException;
-
 /**
  * Dispatcher acts as the bridge between the transport layer and
  * the actual container layer. This layer is capable of transforming
@@ -36,10 +34,8 @@ public interface ContainerDispatcher {
    * Dispatches commands to container layer.
    * @param msg - Command Request
    * @return Command Response
-   * @throws IOException
    */
-  ContainerCommandResponseProto dispatch(ContainerCommandRequestProto msg)
-      throws IOException;
+  ContainerCommandResponseProto dispatch(ContainerCommandRequestProto msg);
 
   /**
    * Initialize the Dispatcher.


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