HDFS-8074 Define a system-wide default EC schema. Contributed by Kai Zheng

hadoop-common-project/hadoop-common/src/main/conf/ecschema-def.xml

@@ -27,11 +27,6 @@ You can modify and remove those not used yet, or add new ones.
 -->
 
 <schemas>
-  <schema name="RS-6-3">
-    <k>6</k>
-    <m>3</m>
-    <codec>RS</codec>
-  </schema>
   <schema name="RS-10-4">
     <k>10</k>
     <m>4</m>

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/ECSchema.java

@@ -23,12 +23,12 @@
 /**
  * Erasure coding schema to housekeeper relevant information.
  */
-public class ECSchema {
+public final class ECSchema {
   public static final String NUM_DATA_UNITS_KEY = "k";
   public static final String NUM_PARITY_UNITS_KEY = "m";
   public static final String CODEC_NAME_KEY = "codec";
   public static final String CHUNK_SIZE_KEY = "chunkSize";
-  public static final int DEFAULT_CHUNK_SIZE = 64 * 1024; // 64K
+  public static final int DEFAULT_CHUNK_SIZE = 256 * 1024; // 256K
 
   private String schemaName;
   private String codecName;
@@ -81,6 +81,18 @@ public ECSchema(String schemaName, Map<String, String> options) {
     initWith(codecName, dataUnits, parityUnits, options);
   }
 
+  /**
+   * Constructor with key parameters provided.
+   * @param schemaName
+   * @param codecName
+   * @param numDataUnits
+   * @param numParityUnits
+   */
+  public ECSchema(String schemaName, String codecName,
+                  int numDataUnits, int numParityUnits) {
+    this(schemaName, codecName, numDataUnits, numParityUnits, null);
+  }
+
   /**
    * Constructor with key parameters provided. Note the options may contain
    * additional information for the erasure codec to interpret further.
@@ -200,4 +212,45 @@ public String toString() {
 
     return sb.toString();
   }
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+
+    ECSchema ecSchema = (ECSchema) o;
+
+    if (numDataUnits != ecSchema.numDataUnits) {
+      return false;
+    }
+    if (numParityUnits != ecSchema.numParityUnits) {
+      return false;
+    }
+    if (chunkSize != ecSchema.chunkSize) {
+      return false;
+    }
+    if (!schemaName.equals(ecSchema.schemaName)) {
+      return false;
+    }
+    if (!codecName.equals(ecSchema.codecName)) {
+      return false;
+    }
+    return options.equals(ecSchema.options);
+  }
+
+  @Override
+  public int hashCode() {
+    int result = schemaName.hashCode();
+    result = 31 * result + codecName.hashCode();
+    result = 31 * result + options.hashCode();
+    result = 31 * result + numDataUnits;
+    result = 31 * result + numParityUnits;
+    result = 31 * result + chunkSize;
+
+    return result;
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/CHANGES-HDFS-EC-7285.txt

@@ -52,4 +52,6 @@
     manage EC zones (Zhe Zhang)
 
     HDFS-8023. Erasure Coding: retrieve eraure coding schema for a file from
-    NameNode (vinayakumarb)
+    NameNode (vinayakumarb)
+    
+    HDFS-8074. Define a system-wide default EC schema. (Kai Zheng)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ECSchemaManager.java

@@ -0,0 +1,62 @@
+/**
+ * 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.hdfs.server.namenode;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.io.erasurecode.ECSchema;
+
+/**
+ * This manages EC schemas predefined and activated in the system. It loads from
+ * predefined ones in XML and syncs with persisted ones in NameNode image.
+ *
+ * This class is instantiated by the FSNamesystem.
+ */
+@InterfaceAudience.LimitedPrivate({"HDFS"})
+public final class ECSchemaManager {
+
+  private static final int DEFAULT_DATA_BLOCKS = 6;
+  private static final int DEFAULT_PARITY_BLOCKS = 3;
+  private static final String DEFAULT_CODEC_NAME = "rs";
+  private static final String DEFAULT_SCHEMA_NAME = "SYS-DEFAULT-RS-6-3";
+
+  private static ECSchema SYS_DEFAULT_SCHEMA = new ECSchema(DEFAULT_SCHEMA_NAME,
+      DEFAULT_CODEC_NAME, DEFAULT_DATA_BLOCKS, DEFAULT_PARITY_BLOCKS);
+
+  /**
+   * Get system-wide default EC schema, which can be used by default when no
+   * schema is specified for an EC zone.
+   * @return schema
+   */
+  public static ECSchema getSystemDefaultSchema() {
+    return SYS_DEFAULT_SCHEMA;
+  }
+
+  /**
+   * Tell the specified schema is the system default one or not.
+   * @param schema
+   * @return true if it's the default false otherwise
+   */
+  public static boolean isSystemDefault(ECSchema schema) {
+    if (schema == null) {
+      throw new IllegalArgumentException("Invalid schema parameter");
+    }
+
+    // schema name is the identifier, but for safety we check all properties.
+    return SYS_DEFAULT_SCHEMA.equals(schema);
+  }
+}