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Main functionality for HBase
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/**
 *
 * 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.hadoop.hbase.coprocessor;

import java.io.IOException;
import java.util.List;

import org.apache.hadoop.hbase.CellScanner;
import org.apache.hadoop.hbase.Coprocessor;
import org.apache.hadoop.hbase.MetaMutationAnnotation;
import org.apache.hadoop.hbase.client.Mutation;
import org.apache.hadoop.hbase.protobuf.generated.AdminProtos.WALEntry;
import org.apache.hadoop.hbase.regionserver.Region;
import org.apache.hadoop.hbase.replication.ReplicationEndpoint;

public interface RegionServerObserver extends Coprocessor {

  /**
   * Called before stopping region server.
   * @param env An instance of RegionServerCoprocessorEnvironment
   * @throws IOException Signals that an I/O exception has occurred.
   */
  void preStopRegionServer(
    final ObserverContext env)
    throws IOException;

  /**
   * Called before the regions merge. 
   * Call {@link org.apache.hadoop.hbase.coprocessor.ObserverContext#bypass()} to skip the merge.
   * @throws IOException if an error occurred on the coprocessor
   * @param ctx
   * @param regionA
   * @param regionB
   * @throws IOException
   */
  void preMerge(final ObserverContext ctx,
      final Region regionA, final Region regionB) throws IOException;

  /**
   * called after the regions merge.
   * @param c
   * @param regionA
   * @param regionB
   * @param mergedRegion
   * @throws IOException
   */
  void postMerge(final ObserverContext c,
      final Region regionA, final Region regionB, final Region mergedRegion) throws IOException;

  /**
   * This will be called before PONR step as part of regions merge transaction. Calling
   * {@link org.apache.hadoop.hbase.coprocessor.ObserverContext#bypass()} rollback the merge
   * @param ctx
   * @param regionA
   * @param regionB
   * @param metaEntries mutations to execute on hbase:meta atomically with regions merge updates. 
   *        Any puts or deletes to execute on hbase:meta can be added to the mutations.
   * @throws IOException
   */
  void preMergeCommit(final ObserverContext ctx,
      final Region regionA, final Region regionB,
      @MetaMutationAnnotation List metaEntries) throws IOException;

  /**
   * This will be called after PONR step as part of regions merge transaction.
   * @param ctx
   * @param regionA
   * @param regionB
   * @param mergedRegion
   * @throws IOException
   */
  void postMergeCommit(final ObserverContext ctx,
      final Region regionA, final Region regionB, final Region mergedRegion) throws IOException;

  /**
   * This will be called before the roll back of the regions merge.
   * @param ctx
   * @param regionA
   * @param regionB
   * @throws IOException
   */
  void preRollBackMerge(final ObserverContext ctx,
      final Region regionA, final Region regionB) throws IOException;

  /**
   * This will be called after the roll back of the regions merge.
   * @param ctx
   * @param regionA
   * @param regionB
   * @throws IOException
   */
  void postRollBackMerge(final ObserverContext ctx,
      final Region regionA, final Region regionB) throws IOException;

  /**
   * This will be called before executing user request to roll a region server WAL.
   * @param ctx An instance of ObserverContext
   * @throws IOException Signals that an I/O exception has occurred.
   */
  void preRollWALWriterRequest(final ObserverContext ctx)
      throws IOException;

  /**
   * This will be called after executing user request to roll a region server WAL.
   * @param ctx An instance of ObserverContext
   * @throws IOException Signals that an I/O exception has occurred.
   */
  void postRollWALWriterRequest(final ObserverContext ctx)
      throws IOException;

  /**
   * This will be called after the replication endpoint is instantiated.
   * @param ctx
   * @param endpoint - the base endpoint for replication
   * @return the endpoint to use during replication.
   */
  ReplicationEndpoint postCreateReplicationEndPoint(
      ObserverContext ctx, ReplicationEndpoint endpoint);

  /**
   * This will be called before executing replication request to shipping log entries.
   * @param ctx An instance of ObserverContext
   * @param entries list of WALEntries to replicate
   * @param cells Cells that the WALEntries refer to (if cells is non-null)
   * @throws IOException Signals that an I/O exception has occurred.
   */
  void preReplicateLogEntries(final ObserverContext ctx,
      List entries, CellScanner cells) throws IOException;

  /**
   * This will be called after executing replication request to shipping log entries.
   * @param ctx An instance of ObserverContext
   * @param entries list of WALEntries to replicate
   * @param cells Cells that the WALEntries refer to (if cells is non-null)
   * @throws IOException Signals that an I/O exception has occurred.
   */
  void postReplicateLogEntries(final ObserverContext ctx,
      List entries, CellScanner cells) throws IOException;
}