1 /**
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 */
18
19 package org.apache.hadoop.hbase.client;
20
21 import org.apache.hadoop.hbase.classification.InterfaceAudience;
22 import org.apache.hadoop.hbase.classification.InterfaceStability;
23
24 /**
25 * Consistency defines the expected consistency level for an operation.
26 */
27 @InterfaceAudience.Public
28 @InterfaceStability.Evolving
29 public enum Consistency {
30 // developer note: Do not reorder. Client.proto#Consistency depends on this order
31 /**
32 * Strong consistency is the default consistency model in HBase,
33 * where reads and writes go through a single server which serializes
34 * the updates, and returns all data that was written and ack'd.
35 */
36 STRONG,
37
38 /**
39 * Timeline consistent reads might return values that may not see
40 * the most recent updates. Write transactions are always performed
41 * in strong consistency model in HBase which guarantees that transactions
42 * are ordered, and replayed in the same order by all copies of the data.
43 * In timeline consistency, the get and scan requests can be answered from data
44 * that may be stale.
45 * <br>
46 * The client may still observe transactions out of order if the requests are
47 * responded from different servers.
48 */
49 TIMELINE,
50 }