不正确实现Hbase协处理器导致难以排查的问题

结论

在2.0之后的版本实现hbase.coprocessor.region.classes类型的协处理器时，需要同时实现org.apache.hadoop.hbase.coprocessor.RegionCoprocessor和org.apache.hadoop.hbase.coprocessor.RegionObserver两个接口，并重写org.apache.hadoop.hbase.coprocessor.RegionCoprocessor#getRegionObserver构造器。示例见官方文档: https://hbase.apache.org/book.html#cp_example

public class RegionObserverExample implements RegionCoprocessor, RegionObserver {

    private static final byte[] ADMIN = Bytes.toBytes("admin");
    private static final byte[] COLUMN_FAMILY = Bytes.toBytes("details");
    private static final byte[] COLUMN = Bytes.toBytes("Admin_det");
    private static final byte[] VALUE = Bytes.toBytes("You can't see Admin details");

    @Override
    public Optional<RegionObserver> getRegionObserver() {
      return Optional.of(this);
    }

    @Override
    public void preGetOp(final ObserverContext<RegionCoprocessorEnvironment> e, final Get get, final List<Cell> results)
    throws IOException {

        if (Bytes.equals(get.getRow(),ADMIN)) {
            Cell c = CellUtil.createCell(get.getRow(),COLUMN_FAMILY, COLUMN,
            System.currentTimeMillis(), (byte)4, VALUE);
            results.add(c);
            e.bypass();
        }
    }
}

值得注意的是：由于Java8的接口使用default关键字可以提供默认实现，因此在Hbase2.0之后的协处理器部分以上述两个接口替换掉了原有的BaseRegionObserver。然而，官方文档对该部分的描述，却在13.4.1. Changes of Note!一节中的Coprocessor APIs have changed in HBase 2.0+部分。

测试

有趣的是，如果在实际的开发中，我们没有注意到这个规定，没有看到官方文档的这个位置，而是仅仅根据源码的线索实现RegionObserver接口然后直接部署，那会怎么样呢？

1. 创建表

   项	值
   命名空间	clgns
   表	test_coprocessor
   列族	f1

2. 新建项目，添加maven依赖

   
   <project xmlns="http://maven.apache.org/POM/4.0.0"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
       <modelVersion>4.0.0modelVersion>
   
       <groupId>xyz.xibladegroupId>
       <artifactId>test_coprocessorartifactId>
       <version>1.0version>
   
       <properties>
           <project.build.sourceEncoding>UTF-8project.build.sourceEncoding>
           <project.reporting.outputEncoding>UTF-8project.reporting.outputEncoding>
           <maven.compiler.source>1.8maven.compiler.source>
           <maven.compiler.target>1.8maven.compiler.target>
           <java.version>1.8java.version>
       properties>
       <dependencies>
           
           <dependency>
               <groupId>org.apache.hbasegroupId>
               <artifactId>hbase-clientartifactId>
               <version>2.1.10version>
           dependency>
           
           <dependency>
               <groupId>org.apache.hbasegroupId>
               <artifactId>hbase-serverartifactId>
               <version>2.1.10version>
           dependency>
       dependencies>
   project>
   

3. 在同一包下实现三个类：

   1. Common

      package xyz.xiblade.test_coprocessor;
      
      import org.apache.hadoop.hbase.TableName;
      import org.apache.hadoop.hbase.client.Put;
      import org.apache.hadoop.hbase.client.Table;
      import org.apache.hadoop.hbase.coprocessor.ObserverContext;
      import org.apache.hadoop.hbase.coprocessor.RegionCoprocessorEnvironment;
      import org.apache.hadoop.hbase.util.Bytes;
      
      import java.io.IOException;
      
      class Common {
          private static final String CALL_LOG_TABLE_NAME = "clgns:test_coprocessor";
          private static final String FAMILY = "f1";
          private static final String COLUMN = "dummy";
      
          static void insertTestData(ObserverContext<RegionCoprocessorEnvironment> c, String data) throws IOException {
              // 比较当前执行表是否为测试表
              String targetTableName = TableName.valueOf(CALL_LOG_TABLE_NAME).getNameAsString();
              String currentTableName = c.getEnvironment().getRegion().getRegionInfo().getTable().getNameAsString();
              if(!targetTableName.equals(currentTableName)){
                  return;
              }
              // 构造Put向测试表插入数据
              Put nput = new Put(Bytes.toBytes(data));
              nput.addColumn(Bytes.toBytes(FAMILY), Bytes.toBytes(COLUMN), Bytes.toBytes(data));
              TableName tn = TableName.valueOf(CALL_LOG_TABLE_NAME);
              Table t = c.getEnvironment().createConnection(c.getEnvironment().getConfiguration()).getTable(tn);
              t.put(nput);
          }
      }
      

   2. NiceOne

      	package xyz.xiblade.test_coprocessor;
      	
      	import org.apache.hadoop.hbase.client.Durability;
      	import org.apache.hadoop.hbase.client.Put;
      	import org.apache.hadoop.hbase.coprocessor.ObserverContext;
      	import org.apache.hadoop.hbase.coprocessor.RegionCoprocessor;
      	import org.apache.hadoop.hbase.coprocessor.RegionCoprocessorEnvironment;
      	import org.apache.hadoop.hbase.coprocessor.RegionObserver;
      	import org.apache.hadoop.hbase.wal.WALEdit;
      	
      	import java.io.IOException;
      	import java.util.Optional;
      	
      	public class NiceOne implements RegionCoprocessor, RegionObserver {
      	
      	    @Override
      	    public Optional<RegionObserver> getRegionObserver() {
      	        return Optional.of(this);
      	    }
      	
      	    @Override
      	    public void postPut(ObserverContext<RegionCoprocessorEnvironment> c,
      	                        Put put,
      	                        WALEdit edit,
      	                        Durability durability) throws IOException {
      	        Common.insertTestData(c, "nice");
      	        c.bypass();
      	    }
      	}
      	```
      

   3. AwfulOne

      	package xyz.xiblade.test_coprocessor;
      	
      	import org.apache.hadoop.hbase.client.Durability;
      	import org.apache.hadoop.hbase.client.Put;
      	import org.apache.hadoop.hbase.coprocessor.ObserverContext;
      	import org.apache.hadoop.hbase.coprocessor.RegionCoprocessorEnvironment;
      	import org.apache.hadoop.hbase.coprocessor.RegionObserver;
      	import org.apache.hadoop.hbase.wal.WALEdit;
      	
      	import java.io.IOException;
      	
      	public class AwfulOne implements RegionObserver {
      	
      	    @Override
      	    public void postPut(ObserverContext<RegionCoprocessorEnvironment> c,
      	                        Put put,
      	                        WALEdit edit,
      	                        Durability durability) throws IOException {
      	        Common.insertTestData(c, "awful");
      	    }
      	}
      

4. 在集群中hbase-site.xml添加如下配置

   <property>
   	<name>hbase.coprocessor.region.classesname>
   	<value>xyz.xiblade.test_coprocessor.AwfulOne,xyz.xiblade.test_coprocessor.NiceOnevalue>
   property>
   

5. 打包项目，拷贝至hbase根目录\lib下，启动集群

6. 插入数据

   put 'clgns:test_coprocessor', 'this_is_the_rowkey', 'f1', 'this_is_the_data'
   

   可以看到put过程会被阻塞

7. 在另一个命令行窗口连接hbase shell，查看数据：

   scan 'clgns:test_coprocessor'
   

   可以看到结果：

   hbase(main):001:0> scan 'clgns:test_coprocessor'
   ROW                                                                  COLUMN+CELL                                                                                                                                                                                              
    nice                                                                column=f1:dummy, timestamp=1590328963702, value=nice                                                                                                                                                     
    this_is_the_rowkey                                                  column=f1:, timestamp=1590328941153, value=this_is_the_data                                                                                                                                              
   2 row(s)
   Took 2.3676 seconds 
   

   说明协处理器AwfulOne无法成功地运行，并且其存在并不会立即将RegionServer异常中断。造成排查的难度加大。