问题导读:
1.hbase协处理器分为几种?
2.钩子分为几种,各自的作用是什么?
3.你认为如何将数据插入索引表?
HBase在0.92之后引入了coprocessors,提供了一系列的钩子,让我们能够轻易实现访问控制和二级索引的特性。下面简单介绍下两种coprocessors,第一种是Observers,它实际类似于触发器,第二种是Endpoint,它类似与存储过程。由于这里只用到了Observers,所以只介绍Observers,想要更详细的介绍请查阅(https://blogs.apache.org/hbase/entry/coprocessor_introduction)。observers分为三种:
RegionObserver:提供数据操作事件钩子;
WALObserver:提供WAL(write ahead log)相关操作事件钩子;
MasterObserver:提供DDL操作事件钩子。
相关接口请参阅hbase api。
下面给出一个例子,该例子使用RegionObserver实现在写主表之前将索引数据先写到另外一个表:
- package com.dengchuanhua.testhbase;
-
- import java.io.IOException;
- import java.util.Iterator;
- import java.util.List;
-
- import org.apache.hadoop.hbase.CoprocessorEnvironment;
- import org.apache.hadoop.hbase.KeyValue;
- import org.apache.hadoop.hbase.client.HTable;
- 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;
-
- public class TestCoprocessor extends BaseRegionObserver {
-
- private HTable table = null;
-
- @Override
- public void start(CoprocessorEnvironment env) throws IOException {
- // pool = new HTablePool(env.getConfiguration(), 10);
- table = new HTable(env.getConfiguration(), "test_index");
- }
-
- @Override
- public void prePut(final ObserverContext<RegionCoprocessorEnvironment> e,
- final Put put, final WALEdit edit, final boolean writeToWAL)
- throws IOException {
- // set configuration
- // Configuration conf = new Configuration();
- // need conf.set...
-
- List<KeyValue> kv = put.get("family".getBytes(), "cog".getBytes());
- Iterator<KeyValue> kvItor = kv.iterator();
- while (kvItor.hasNext()) {
- KeyValue tmp = kvItor.next();
- Put indexPut = new Put(tmp.getValue());
- indexPut.add("family".getBytes(), "cog".getBytes(), tmp.getRow());
- table.put(indexPut);
- table.flushCommits();
- }
- }
-
- @Override
- public void stop(CoprocessorEnvironment env) throws IOException {
- table.close();
- }
- }
复制代码
写完后要加载到table里面去,先把该文件打包成test.jar并上传到hdfs的/demo路径下,然后操作如下:
1. disable ‘testTable’
2. alter ‘testTable’, METHOD=>’table_att’,'coprocessor’=>’hdfs:///demo/test.jar|com.dengchuanhua.testhbase.TestCoprocessor|1001′
3. enable ‘testTable’
然后往testTable里面插数据就会自动往indexTableName写数据了。
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http://491569462-qq-com.iteye.com/blog/1923166
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