| /* |
| * 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.druid.hll; |
| |
| import com.google.common.hash.HashFunction; |
| import com.google.common.hash.Hashing; |
| import org.apache.druid.java.util.common.StringUtils; |
| |
| /** |
| * Contains data hashing methods used before applying Hyper Log Log. |
| * |
| * {@link HyperLogLogCollector#add(byte[])} requires hashed value on input. This class makes it easier to achieve |
| * consistent value hashing for both internal aggregation and external hashing for pre-computed aggregation. |
| * <p> |
| * By default 128-bit murmur3 algorithm, x64 variant is used. Implementation is thread safe. |
| * <p> |
| * Caution! changing of implementation may cause improper cardinality estimation between data hashed with different |
| * versions. |
| */ |
| public class HyperLogLogHash |
| { |
| private static final HyperLogLogHash DEFAULT = new HyperLogLogHash(Hashing.murmur3_128()); |
| |
| public static HyperLogLogHash getDefault() |
| { |
| return DEFAULT; |
| } |
| |
| private final HashFunction hashFunction; |
| |
| public HyperLogLogHash(HashFunction hashFunction) |
| { |
| this.hashFunction = hashFunction; |
| } |
| |
| public byte[] hash(byte[] rawValue) |
| { |
| return hashFunction.hashBytes(rawValue).asBytes(); |
| } |
| |
| public byte[] hash(String rawValue) |
| { |
| return hash(StringUtils.toUtf8(rawValue)); |
| } |
| } |