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 */
018
019package org.apache.hadoop.hbase.client;
020
021import org.apache.yetus.audience.InterfaceAudience;
022
023/**
024 * Consistency defines the expected consistency level for an operation.
025 */
026@InterfaceAudience.Public
027public enum Consistency {
028  // developer note: Do not reorder. Client.proto#Consistency depends on this order
029  /**
030   * Strong consistency is the default consistency model in HBase,
031   * where reads and writes go through a single server which serializes
032   * the updates, and returns all data that was written and ack'd.
033   */
034  STRONG,
035
036  /**
037   * Timeline consistent reads might return values that may not see
038   * the most recent updates. Write transactions are always performed
039   * in strong consistency model in HBase which guarantees that transactions
040   * are ordered, and replayed in the same order by all copies of the data.
041   * In timeline consistency, the get and scan requests can be answered from data
042   * that may be stale.
043   * <br>
044   * The client may still observe transactions out of order if the requests are
045   * responded from different servers.
046   */
047  TIMELINE,
048}