HBase协处理器实战

HBase协处理器实战

1.概念

HBase的coprocessor分为两类，Observer和EndPoint。HBase中的协处理器可以被理解为Mysql中的触发器或者是存储过程。其中，Observer相当于触发器，代码部署在服务端，相当于对API调用的代理。

2.实战

step 1.编写Java程序

这里使用RegionObserver作为示例，简单介绍RegionServer的JavaAPI的编写。
- MyRegionObserver类

package TwitBase.hbase;

import com.sun.org.apache.commons.logging.Log;
import com.sun.org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellUtil;
import org.apache.hadoop.hbase.CoprocessorEnvironment;
import org.apache.hadoop.hbase.client.Delete;
import org.apache.hadoop.hbase.client.Durability;
import org.apache.hadoop.hbase.client.Put;
import org.apache.hadoop.hbase.coprocessor.BaseRegionObserver;
import org.apache.hadoop.hbase.coprocessor.ObserverContext;
import org.apache.hadoop.hbase.coprocessor.RegionCoprocessorEnvironment;
import org.apache.hadoop.hbase.regionserver.wal.WALEdit;
import org.apache.hadoop.hbase.util.Bytes;

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

public class MyRegionObserver extends BaseRegionObserver {
    private static final Log LOG = LogFactory.getLog(MyRegionObserver.class);

    private RegionCoprocessorEnvironment env = null;

    // 设定只有F族下的列才能被操作，且A列只写，B列只读。的语言
    private static final String FAMILY_NAME = "F";
    private static final String ONLY_PUT_COL = "A";
    private static final String ONLY_READ_COL = "B";

    // 协处理器是运行于region中的，每一个region都会加载协处理器
    // 这个方法会在regionserver打开region时候执行（还没有真正打开）
    @Override
    public void start(CoprocessorEnvironment e) throws IOException {
        env = (RegionCoprocessorEnvironment) e;
    }

    // 这个方法会在regionserver关闭region时候执行（还没有真正关闭）
    @Override
    public void stop(CoprocessorEnvironment e) throws IOException {
        //nothing to do here
    }

    /**
     * 需求
     * 1.不允许直接插入B列
     * 2.只能插入A列
     * 3.插入的数据必须为整数
     * 4.插入A列的时候自动插入B列
     */
    @Override
    public void prePut(final ObserverContext e,
                       final Put put, final WALEdit edit, final Durability durability)
            throws IOException {

        //首先查看单个put中是否有 对只读列的写操作 --->即检查B列
        //这里的put是一个操作（作为一个函数的参数存在），对表的一些行操作
        List cells = put.get(Bytes.toBytes(FAMILY_NAME),
                Bytes.toBytes(ONLY_READ_COL));
        if (cells != null && cells.size() != 0) {
            LOG.warn("User is not allowed to write read_only col.");
            throw new IOException("User is not allowed to write read_only col.");
        }

        // 检查A列
        //这里的get()方法是通过能够匹配的column family and qualifier去寻找一个put操作
        cells = put.get(Bytes.toBytes(FAMILY_NAME),
                Bytes.toBytes(ONLY_PUT_COL));
        if (cells == null || cells.size() == 0) {
            //当不存在对于A列的操作的时候则不做任何的处理，直接放行即可
            LOG.info("Column A don't have operation, just do it.");
            return;
        }

        //当A列存在的情况下，再进行值的检查，查看是否插入了整数
        byte[] aValue = null;
        for (Cell cell : cells) {
            try {
                aValue = CellUtil.cloneValue(cell);
                LOG.warn("aValue = " + Bytes.toString(aValue));
                Integer.valueOf(Bytes.toString(aValue));
            } catch (Exception e1) {
                LOG.warn("Can not put un number value to A col.");
                throw new IOException("Can not put un number value to A col.");
            }
        }

        //当一切都通过时，再去构建B列的值，因为按照需求，插入A列的时候需要同时插入B列
        LOG.info("B col also been put value!");
        put.addColumn(Bytes.toBytes(FAMILY_NAME),
                Bytes.toBytes(ONLY_READ_COL), aValue);
    }

    /**
     * 需求
     * 1.不能直接删除B列
     * 2.只能删除A列
     * 3.删除A列的时候需要同步删除B列
     * 4.preDelete这个操作肯定是针对delete操作，所以delete是其一个参数
     */
    @Override
    public void preDelete(
            final ObserverContext e,
            final Delete delete, final WALEdit edit, final Durability durability)
            throws IOException{

        //首先查看是否对于B列进行了指定删除
        List cells = delete.getFamilyCellMap().get(Bytes.toBytes(FAMILY_NAME));
        if (cells == null || cells.size() == 0) {
            //如果客户端没有针对于FAMILY_NAME列族的操作则不用关心，让其继续操作即可。
            LOG.info("NO F family operation ,just do it.");
            return;
        }

        // 开始检查F列族内的操作情况
        byte[] qualifierName = null;
        boolean aDeleteFlg = false;
        for (Cell cell : cells) {
            qualifierName = CellUtil.cloneQualifier(cell);

            // 检查是否对B列进行了删除，这个是不允许的
            if (Arrays.equals(qualifierName, Bytes.toBytes(ONLY_READ_COL))) {
                LOG.info("Can not delete read only B col.");
                throw new IOException("Can not delete read only B col.");
            }

            // 检查是否存在对于A队列的删除
            if (Arrays.equals(qualifierName, Bytes.toBytes(ONLY_PUT_COL))) {
                LOG.info("there is A col in delete operation!");
                aDeleteFlg = true;
            }
        }
        // 如果对于A列有删除，则需要对B列也要删除
        if (aDeleteFlg)
        {
            LOG.info("B col also been deleted!");
            delete.addColumn(Bytes.toBytes(FAMILY_NAME), Bytes.toBytes(ONLY_READ_COL));
        }
    }
}

这里对文件pom.xml中的内容不做介绍，只要适合自己集群中的大数据组件的依赖即可。将该程序打包，提交到集群hdfs上。

step 2.使用Hbase shell创建表

创建表coprocessor_table，列族为F。

hbase(main):022:0> create 'coprocessor_table','F'
0 row(s) in 1.2450 seconds

=> Hbase::Table - coprocessor_table

为表添加协处理器

hbase(main):023:0> alter 'coprocessor_table',METHOD =>'table_att','coprocessor'=>'hdfs://192.168.211.3:9000/MyHBaseInAction-1.0-SNAPSHOT.jar|HBaseIA.TwitBase.hbase.MyRegionObserver|1001'
Updating all regions with the new schema...
1/1 regions updated.
Done.
0 row(s) in 1.9270 seconds

向表coprocessoer中put信息

hbase(main):024:0> put 'coprocessor_table','row1','F:A',123 
0 row(s) in 0.0090 seconds

扫描全表

hbase(main):025:0> scan 'coprocessor_table'
ROW                   COLUMN+CELL                                                  
 row1                 column=F:A, timestamp=1529434234158, value=123               
 row1                 column=F:B, timestamp=1529434234158, value=123               
1 row(s) in 0.0130 seconds

可以看到，这里列族F中列B也被添加了数据（这就是协处理的作用）
检验是否可以向指定表coprocessor_table下的指定列族F的指定列A，插入非数字内容

hbase(main):028:0> put 'coprocessor_table','row1','F:A','dfs'

ERROR: Failed 1 action: IOException: 1 time, servers with issues: littlelawson,16020,1529427401818

Here is some help for this command:
Put a cell 'value' at specified table/row/column and optionally
timestamp coordinates.  To put a cell value into table 'ns1:t1' or 't1'
at row 'r1' under column 'c1' marked with the time 'ts1', do:

  hbase> put 'ns1:t1', 'r1', 'c1', 'value'
  hbase> put 't1', 'r1', 'c1', 'value'
  hbase> put 't1', 'r1', 'c1', 'value', ts1
  hbase> put 't1', 'r1', 'c1', 'value', {ATTRIBUTES=>{'mykey'=>'myvalue'}}
  hbase> put 't1', 'r1', 'c1', 'value', ts1, {ATTRIBUTES=>{'mykey'=>'myvalue'}}
  hbase> put 't1', 'r1', 'c1', 'value', ts1, {VISIBILITY=>'PRIVATE|SECRET'}

The same commands also can be run on a table reference. Suppose you had a reference
t to table 't1', the corresponding command would be:

  hbase> t.put 'r1', 'c1', 'value', ts1, {ATTRIBUTES=>{'mykey'=>'myvalue'}}

检查是否可以向表中的列族中的B列插入数据：

hbase(main):029:0> put 'coprocessor_table','row1','F:B',456

ERROR: Failed 1 action: IOException: 1 time, servers with issues: littlelawson,16020,1529427401818

Here is some help for this command:
Put a cell 'value' at specified table/row/column and optionally
timestamp coordinates.  To put a cell value into table 'ns1:t1' or 't1'
at row 'r1' under column 'c1' marked with the time 'ts1', do:

  hbase> put 'ns1:t1', 'r1', 'c1', 'value'
  hbase> put 't1', 'r1', 'c1', 'value'
  hbase> put 't1', 'r1', 'c1', 'value', ts1
  hbase> put 't1', 'r1', 'c1', 'value', {ATTRIBUTES=>{'mykey'=>'myvalue'}}
  hbase> put 't1', 'r1', 'c1', 'value', ts1, {ATTRIBUTES=>{'mykey'=>'myvalue'}}
  hbase> put 't1', 'r1', 'c1', 'value', ts1, {VISIBILITY=>'PRIVATE|SECRET'}

The same commands also can be run on a table reference. Suppose you had a reference
t to table 't1', the corresponding command would be:

  hbase> t.put 'r1', 'c1', 'value', ts1, {ATTRIBUTES=>{'mykey'=>'myvalue'}}

3.注意

需要注意的地方有下：
- 执行命令：alter 'coprocessor_table',METHOD =>'table_att','coprocessor'=>'hdfs://192.168.211.3:9000/MyHBaseInAction-1.0-SNAPSHOT.jar|HBaseIA.TwitBase.hbase.MyRegionObserver|1001'这里需要清楚的是，将Observer所在的jar包放到了hdfs上，所以需要指定hdfs路径，否则报错如下：

ERROR: org.apache.hadoop.hbase.DoNotRetryIOException: java.net.UnknownHostException:
MyHBaseInAction-1.0-SNAPSHOT.jar Set hbase.table.sanity.checks to false at conf or 
table descriptor if you want to bypass sanity checks
....

• 上述命令中的METHOD不能小写，否则报错。【HBase是大小写敏感的】
• 本博客借鉴了网上的一些博客，若有侵权，请联系笔者。