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.coprocessor;
019
020import java.io.IOException;
021import org.apache.hadoop.conf.Configuration;
022import org.apache.hadoop.hbase.CoprocessorEnvironment;
023import org.apache.hadoop.hbase.HBaseInterfaceAudience;
024import org.apache.hadoop.hbase.ServerName;
025import org.apache.hadoop.hbase.client.Connection;
026import org.apache.hadoop.hbase.metrics.MetricRegistry;
027import org.apache.yetus.audience.InterfaceAudience;
028import org.apache.yetus.audience.InterfaceStability;
029
030@InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
031@InterfaceStability.Evolving
032public interface MasterCoprocessorEnvironment extends CoprocessorEnvironment<MasterCoprocessor> {
033  /**
034   * @return Hosting Server's ServerName
035   */
036  ServerName getServerName();
037
038  /**
039   * Returns the hosts' Connection to the Cluster. <b>Do not close! This is a shared connection with
040   * the hosting server. Throws {@link UnsupportedOperationException} if you try to close or abort
041   * it</b>. For light-weight usage only. Heavy-duty usage will pull down the hosting RegionServer
042   * responsiveness as well as that of other Coprocessors making use of this Connection. Use to
043   * create table on start or to do administrative operations. Coprocessors should create their own
044   * Connections if heavy usage to avoid impinging on hosting Server operation. To create a
045   * Connection or if a Coprocessor requires a region with a particular Configuration, use
046   * {@link org.apache.hadoop.hbase.client.ConnectionFactory} or
047   * {@link #createConnection(Configuration)}}.
048   * <p>
049   * Be aware that operations that make use of this Connection are executed as the RegionServer
050   * User, the hbase super user that started this server process. Exercise caution running
051   * operations as this User (See {@link #createConnection(Configuration)}} to run as other than the
052   * RegionServer User).
053   * <p>
054   * Be careful RPC'ing from a Coprocessor context. RPC's will fail, stall, retry, and/or crawl
055   * because the remote side is not online, is struggling or it is on the other side of a network
056   * partition. Any use of Connection from inside a Coprocessor must be able to handle all such
057   * hiccups.
058   * @see #createConnection(Configuration)
059   * @return The host's Connection to the Cluster.
060   */
061  Connection getConnection();
062
063  /**
064   * Creates a cluster connection using the passed Configuration. Creating a Connection is a
065   * heavy-weight operation. The resultant Connection's cache of region locations will be empty.
066   * Therefore you should cache and reuse Connections rather than create a Connection on demand.
067   * Create on start of your Coprocessor. You will have to cast the CoprocessorEnvironment
068   * appropriately to get at this API at start time because Coprocessor start method is passed a
069   * subclass of this CoprocessorEnvironment or fetch Connection using a synchronized accessor
070   * initializing the Connection on first access. Close the returned Connection when done to free
071   * resources. Using this API rather than
072   * {@link org.apache.hadoop.hbase.client.ConnectionFactory#createConnection(Configuration)}
073   * returns a Connection that will short-circuit RPC if the target is a local resource. Use
074   * ConnectionFactory if you don't need this ability.
075   * <p>
076   * Be careful RPC'ing from a Coprocessor context. RPC's will fail, stall, retry, and/or crawl
077   * because the remote side is not online, is struggling or it is on the other side of a network
078   * partition. Any use of Connection from inside a Coprocessor must be able to handle all such
079   * hiccups.
080   * @return Connection created using the passed conf.
081   */
082  Connection createConnection(Configuration conf) throws IOException;
083
084  /**
085   * Returns a MetricRegistry that can be used to track metrics at the master level.
086   * <p>
087   * See ExampleMasterObserverWithMetrics class in the hbase-examples modules for examples of how
088   * metrics can be instantiated and used.
089   * </p>
090   * @return A MetricRegistry for the coprocessor class to track and export metrics.
091   */
092  MetricRegistry getMetricRegistryForMaster();
093}