001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.client;
019
020import org.apache.yetus.audience.InterfaceAudience;
021
022/**
023 * Consistency defines the expected consistency level for an operation.
024 */
025@InterfaceAudience.Public
026public enum Consistency {
027  // developer note: Do not reorder. Client.proto#Consistency depends on this order
028  /**
029   * Strong consistency is the default consistency model in HBase, where reads and writes go through
030   * a single server which serializes the updates, and returns all data that was written and ack'd.
031   */
032  STRONG,
033
034  /**
035   * Timeline consistent reads might return values that may not see the most recent updates. Write
036   * transactions are always performed in strong consistency model in HBase which guarantees that
037   * transactions are ordered, and replayed in the same order by all copies of the data. In timeline
038   * consistency, the get and scan requests can be answered from data that may be stale. <br>
039   * The client may still observe transactions out of order if the requests are responded from
040   * different servers.
041   */
042  TIMELINE,
043}