hbase-common/src/main/java/org/apache/hadoop/hbase/util/Hash.java

   1 /**
   2  *
   3  * Licensed to the Apache Software Foundation (ASF) under one
   4  * or more contributor license agreements.  See the NOTICE file
   5  * distributed with this work for additional information
   6  * regarding copyright ownership.  The ASF licenses this file
   7  * to you under the Apache License, Version 2.0 (the
   8  * "License"); you may not use this file except in compliance
   9  * with the License.  You may obtain a copy of the License at
  10  *
  11  *     http://www.apache.org/licenses/LICENSE-2.0
  12  *
  13  * Unless required by applicable law or agreed to in writing, software
  14  * distributed under the License is distributed on an "AS IS" BASIS,
  15  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  16  * See the License for the specific language governing permissions and
  17  * limitations under the License.
  18  */
  19
  20 package org.apache.hadoop.hbase.util;
  21
  22 import org.apache.hadoop.conf.Configuration;
  23 import org.apache.yetus.audience.InterfaceAudience;
  24 import org.apache.yetus.audience.InterfaceStability;
  25
  26 /**
  27  * This class represents a common API for hashing functions.
  28  */
  29 @InterfaceAudience.Private
  30 @InterfaceStability.Stable
  31 public abstract class Hash {
  32   /** Constant to denote invalid hash type. */
  33   public static final int INVALID_HASH = -1;
  34   /** Constant to denote {@link JenkinsHash}. */
  35   public static final int JENKINS_HASH = 0;
  36   /** Constant to denote {@link MurmurHash}. */
  37   public static final int MURMUR_HASH  = 1;
  38   /** Constant to denote {@link MurmurHash3}. */
  39   public static final int MURMUR_HASH3 = 2;
  40
  41   /**
  42    * This utility method converts String representation of hash function name
  43    * to a symbolic constant. Currently three function types are supported,
  44    * "jenkins", "murmur" and "murmur3".
  45    * @param name hash function name
  46    * @return one of the predefined constants
  47    */
  48   public static int parseHashType(String name) {
  49     if ("jenkins".equalsIgnoreCase(name)) {
  50       return JENKINS_HASH;
  51     } else if ("murmur".equalsIgnoreCase(name)) {
  52       return MURMUR_HASH;
  53     } else if ("murmur3".equalsIgnoreCase(name)) {
  54       return MURMUR_HASH3;
  55     } else {
  56       return INVALID_HASH;
  57     }
  58   }
  59
  60   /**
  61    * This utility method converts the name of the configured
  62    * hash type to a symbolic constant.
  63    * @param conf configuration
  64    * @return one of the predefined constants
  65    */
  66   public static int getHashType(Configuration conf) {
  67     String name = conf.get("hbase.hash.type", "murmur");
  68     return parseHashType(name);
  69   }
  70
  71   /**
  72    * Get a singleton instance of hash function of a given type.
  73    * @param type predefined hash type
  74    * @return hash function instance, or null if type is invalid
  75    */
  76   public static Hash getInstance(int type) {
  77     switch (type) {
  78       case JENKINS_HASH:
  79         return JenkinsHash.getInstance();
  80       case MURMUR_HASH:
  81         return MurmurHash.getInstance();
  82       case MURMUR_HASH3:
  83         return MurmurHash3.getInstance();
  84       default:
  85         return null;
  86     }
  87   }
  88
  89   /**
  90    * Get a singleton instance of hash function of a type
  91    * defined in the configuration.
  92    * @param conf current configuration
  93    * @return defined hash type, or null if type is invalid
  94    */
  95   public static Hash getInstance(Configuration conf) {
  96     int type = getHashType(conf);
  97     return getInstance(type);
  98   }
  99
 100   /**
 101    * Calculate a hash using bytes from HashKey and the provided seed value.
 102    * @param <T>
 103    * @param hashKey key to extract the hash
 104    * @param initval the seed value
 105    * @return hash value
 106    */
 107   public abstract <T> int hash(HashKey<T> hashKey, int initval);
 108 }