hbase高级编程：hbase（新版） 0.985协处理器中的BaseRegionServerObserver

本帖最后由 pig2 于 2014-8-21 07:07 编辑

问题导读
1.协处理分为几种？
2.二者各有什么不同？
3.hbase coprocessor新版中做了哪些改变？

现在hbase的coprocessor有两种完全不同的实现，分别是observer模式与endpoint模式，它们分别对应2000和2001两个issue。我们可以将observer模式看成数据库中的触发器，而endpoint可以看成是存储过程。

关于coprocessor我们可以从类继承关系上看到，如下图所示：

共有旧版本中（0.92）三个Observer对象，即MasterObserver，RegionObserver和WALObserver，新版增加RegionServerObserver。它们的工作原理类似于钩子函数，在真实的函数实现前加入pre()，实现后加入post()方法，来实现对操作进行一些嵌入式的改变。

在新版本中，包括hbase0.96及hbase 0.985（其它版本尚未查看）增加了对象BaseRegionServerObserver
这个类功能：合并两个HRegion

hbase coprocessor的实现分为observer与endpoint，其中observer类似于触发器，主要在服务端工作，而endpoint类似于存储过程，主要在client端工作
observer可以实现权限管理、优先级设置、监控、ddl控制、二级索引等功能，而endpoint可以实现min、mas、avg、sum等功能
coprocessor可以动态加载

附上代码BaseRegionServerObserver代码：

/*
 *
 * Licensed 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.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.hbase.CoprocessorEnvironment;
import org.apache.hadoop.hbase.HBaseInterfaceAudience;
import org.apache.hadoop.hbase.client.Mutation;
import org.apache.hadoop.hbase.regionserver.HRegion;

/**
 * An abstract class that implements RegionServerObserver.
 * By extending it, you can create your own region server observer without
 * overriding all abstract methods of RegionServerObserver.
 */
@InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
@InterfaceStability.Evolving
public class BaseRegionServerObserver implements RegionServerObserver {

  @Override
  public void preStopRegionServer(ObserverContext<RegionServerCoprocessorEnvironment> env)
      throws IOException { }

  @Override
  public void start(CoprocessorEnvironment env) throws IOException { }

  @Override
  public void stop(CoprocessorEnvironment env) throws IOException { }

  @Override
  public void preMerge(ObserverContext<RegionServerCoprocessorEnvironment> ctx, HRegion regionA,
      HRegion regionB) throws IOException { }

  @Override
  public void postMerge(ObserverContext<RegionServerCoprocessorEnvironment> c, HRegion regionA,
      HRegion regionB, HRegion mergedRegion) throws IOException { }

  @Override
  public void preMergeCommit(ObserverContext<RegionServerCoprocessorEnvironment> ctx,
      HRegion regionA, HRegion regionB, List<Mutation> metaEntries) throws IOException { }

  @Override
  public void postMergeCommit(ObserverContext<RegionServerCoprocessorEnvironment> ctx,
      HRegion regionA, HRegion regionB, HRegion mergedRegion) throws IOException { }

  @Override
  public void preRollBackMerge(ObserverContext<RegionServerCoprocessorEnvironment> ctx,
      HRegion regionA, HRegion regionB) throws IOException { }

  @Override
  public void postRollBackMerge(ObserverContext<RegionServerCoprocessorEnvironment> ctx,
      HRegion regionA, HRegion regionB) throws IOException { }

}
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