本文是笔者学习过程中的简单笔记,日后会逐渐增加内容,主要参考资料是《Hbase The Definitive Guide》。
我们可以通过Filter来减少从Server到Client在网络上传输的数据总量,以提升效率。通过HBase的Coprocessor特性,我们甚至可以将计算(computation)移动到数据所在的节点。
Introduction to Coprocessors
coprocessor使你能够直接在每个region server上执行任意的代码。更精确地说,它提供一些通过事件触发的功能,以region为基础执行code;这很像关系型数据库系统中的procedures(存储过程)。
在使用coprocessor时,你需要基于特定的interface创建专门的类,以jar包的形式提供给region server (如:可以将jar包放到$HBASE_HOME/lib/目录下)。这些coprocessor类可以通过配置文件静态加载,也可以在程序代码中动态加载。
corpocessor 框架提供了两种coprocessor基类:
1.Observer
这种coprocessor跟触发器相像:当特定的时间发生时,回调函数就会执行。
RegionObserver
处理数据操纵事件(data manipulationevents),这种coprocessor是和表的region紧密相连的。可以看作DML Coprocessor
MasterObserver
处理数据管理事件,是cluster范围的coprocessor。可以看做DDL Coprocessor
WALObserver
处理 write-ahead log processing 事件
2.Endpoint
The Coprocessor Class
所有的coprocessor类必须实现org.apache.hadoop.hbase.Coprocessor接口。
1.属性
PRIORITY_HIGHEST,PRIORITY_SYSTEM,PRIORITY_USER,PRIORITY_LOWEST四个静态常量表示coprocessor的优先级.值越低优先级越高。
2.方法
start(env) stop(env) :这两个方法在coprocessor开始及退役的时候被调用(these two methods are called when the coprocessor class is started,and eventually when it is decommissioned)
evn参数用来保存coprocessor整个生命周期的状态。
- package org.apache.hadoop.hbase;
-
- import java.io.IOException;
-
- /**
- * Coprocess interface.
- */
- public interface Coprocessor {
- static final int VERSION = 1;
-
- /** Highest installation priority */
- static final int PRIORITY_HIGHEST = 0;
- /** High (system) installation priority */
- static final int PRIORITY_SYSTEM = Integer.MAX_VALUE / 4;
- /** Default installation priority for user coprocessors */
- static final int PRIORITY_USER = Integer.MAX_VALUE / 2;
- /** Lowest installation priority */
- static final int PRIORITY_LOWEST = Integer.MAX_VALUE;
-
- /**
- * Lifecycle state of a given coprocessor instance.
- */
- public enum State {
- UNINSTALLED,
- INSTALLED,
- STARTING,
- ACTIVE,
- STOPPING,
- STOPPED
- }
-
- // Interface
- void start(CoprocessorEnvironment env) throws IOException;
-
- void stop(CoprocessorEnvironment env) throws IOException;
- }
Coprocessor Loading 加载coprocessor
静态加载和动态加载。
静态加载:在hbase-site.xml中做类似下面的配置
- <property>
- <name>hbase.coprocessor.region.classes</name>
- <value>coprocessor.RegionObserverExample,coprocessor.AnotherCoprocessor</value>
- </property>
- <property>
- <name>hbase.coprocessor.master.classes</name>
- <value>coprocessor.MasterObserverExample</value>
- </property>
- <property>
- <name>hbase.coprocessor.wal.classes</name>
- <value>coprocessor.WALObserverExample,bar.foo.MyWALObserver</value>
- </property>
动态加载:通过table descriptor提供的接口实现;看下面的例子,创建表testtable,动态加载RegionObserverExample到该表的region
- public class LoadWithTableDescriptorExample {
-
- public static void main(String[] args) throws IOException
- {
- Configuration conf = HBaseConfiguration.create();
- FileSystem fs = FileSystem.get(conf);
- //coprocessor所在的jar包的存放路径
- Path path = new Path(fs.getUri() + Path.SEPARATOR +"test/coprocessor/"+
- "test.jar");
- //HTableDescriptor
- HTableDescriptor htd = new HTableDescriptor("testtable");
- //addFamily
- htd.addFamily(new HColumnDescriptor("colfam1"));
- //
- //设置要加载的corpocessor
- htd.setValue("COPROCESSOR$1", path.toString() +
- "|" + RegionObserverExample.class.getCanonicalName() +
- "|" + Coprocessor.PRIORITY_USER);
- //
- HBaseAdmin admin = new HBaseAdmin(conf);
-
- //创建表"testtable"
- admin.createTable(htd);
-
- System.out.println("end");
- }
- }
下面是RegionObserverExample类的实现, 编译通过后,将该类打包成test.jar,并上传到hdfs://master:9000/test/coprocessor目录下
- package coprocessor;
-
- import java.io.IOException;
- import java.sql.Date;
- import java.util.List;
- import org.apache.commons.net.ntp.TimeStamp;
- import org.apache.hadoop.hbase.KeyValue;
- import org.apache.hadoop.hbase.client.Get;
- 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.util.Bytes;
-
- public class RegionObserverExample extends
- BaseRegionObserver {
-
- public static final byte[] FIXED_ROW =
- Bytes.toBytes("@@@GETTIME@@@");
- //实现功能:用get查询 "@@@GETTIME@@@"行时,以字节数组形式返回系统时间
- @Override
- public void preGet(
- final ObserverContext<RegionCoprocessorEnvironment> e,
- final Get get, final List<KeyValue> results) throws
- IOException {
- if (Bytes.equals(get.getRow(), FIXED_ROW)) {
- KeyValue kv = new KeyValue(get.getRow(), FIXED_ROW,
- FIXED_ROW,
- Bytes.toBytes(System.currentTimeMillis()));
- results.add(kv);
- }
- }
-
- public static void main(String args[]){
-
- System.out.println("complete!");
- }
- }
Endpoints
前面提到的RegionObserver例子通过已知的row key参数,将列计算功能添加到get请求期间。看起来这足以实现其他功能,比如恩能够返回所有给定列的value的和的聚合函数。然而,RegionObserver并不能实现上述功能,因为row key 决定了由哪个region处理request,这样就只能将计算请求(computation request)发送到单一的server上。
HBase为了克服上述RegionObserver的局限性,由coprocessor框架提供了一个动态调用实现(a dynamic call implementation),称作endpoint concept.
The CoprocessorProtocol interface
The BaseEndpointCoprocessor class
实现一个endpoint包括以下两个步骤
1.Extend the CoprocessorProtocol interface
2.Extend the BaseEndpointCoprocessor class
下面是一个小例子,实现功能:客户端通过远程调用检索每个region的行数和KeyValue的个数。
1.RowCountProtocol interface, code:
- public interface RowCountProtocol extends CoprocessorProtocol {
- //获取行数
- long getRowCount() throws IOException;
- //获取应用Filter后的结果集的行数
- long getRowCount(Filter filter) throws IOException;
- //获取KeyValue的个数
- long getKeyValueCount() throws IOException;
- }
2.RowCountEndPoint class, code:
- public class RowCountEndPoint extends BaseEndpointCoprocessor implements
- RowCountProtocol {
-
- public RowCountEndPoint() {
- // TODO Auto-generated constructor stub
- }
-
- @Override
- public long getRowCount() throws IOException {
- // TODO Auto-generated method stub
- return this.getRowCount(new FirstKeyOnlyFilter());
- }
-
- @Override
- public long getRowCount(Filter filter) throws IOException {
- // TODO Auto-generated method stub
-
-
- return this.getRowCount(filter,false);
- }
-
- @Override
- public long getKeyValueCount() throws IOException {
- // TODO Auto-generated method stub
- return this.getRowCount(null,true);
- }
-
-
- public long getRowCount(Filter filter,boolean countKeyValue) throws IOException {
- // TODO Auto-generated method stub
- Scan scan =new Scan();
- scan.setMaxVersions(1);
- if(filter !=null){
- scan.setFilter(filter);
- }
-
- RegionCoprocessorEnvironment environment=
- (RegionCoprocessorEnvironment) this.getEnvironment();
-
- //使用内部scanner做扫描。
- InternalScanner scanner = environment.getRegion().getScanner(scan);
- //
- long result=0;
-
- //计数
- try{
- boolean done=false;
- List<KeyValue> curValue = new ArrayList<KeyValue>();
- do{
- curValue.clear();
- done=scanner.next(curValue);
- result+=countKeyValue?curValue.size():1;
-
- }while(done);
-
- }catch(Exception e){
- e.printStackTrace();
- }finally{
- scanner.close();
- }
-
- return result;
- }
-
- /**
- * @param args
- */
- public static void main(String[] args) {
- // TODO Auto-generated method stub
- System.out.println("success!");
- }
- }
3.
3.1将上述类打包到my_coprocessor.jar, copy到各个RegionServer节点的 $HBASE_HOME/lib目录下;
3.2修改$HBASE_HOME/conf/hbase-site.xml配置文件,添加如下信息:
- <property>
- <name>hbase.coprocessor.region.classes</name>
- <value>
- coprocessor.RegionObserverExample,
- coprocessor.RowCountEndPoint
- </value>
- </property>
3.3 重启HBase Cluster
4.通过客户端调用之前定义的EndPoint Coprocessor
- public class EndPointExample {
-
- /**
- * @author mango_song
- * @param args
- * @throws IOException
- */
- public static void main(String[] args) throws IOException {
- // TODO Auto-generated method stub
-
- Configuration conf = HBaseConfiguration.create();
-
- HTable table =new HTable(conf,"test");
-
- try {
- //
- /*table.coprocessorExec 函数的描述信息:
- * <RowCountProtocol, Long> Map<byte[], Long> org.apache.hadoop.hbase.client.HTable.coprocessorExec(
- * Class<RowCountProtocol> protocol,
- * byte[] startKey, byte[] endKey,
- * Call<RowCountProtocol, Long> callable)
- * throws IOException, Throwable
- Invoke the passed org.apache.hadoop.hbase.client.coprocessor.Batch.Call
- against the CoprocessorProtocol instances running in the selected regions.
- All regions beginning with the region containing the startKey row,
- through to the region containing the endKey row (inclusive) will be used.
- If startKey or endKey is null, the first and last regions in the table,
- respectively, will be used in the range selection.
- Specified by: coprocessorExec(...) in HTableInterface
- Parameters:
- protocol the CoprocessorProtocol implementation to call
- startKey start region selection with region containing this row
- endKey select regions up to and including the region containing this row
- callable wraps the CoprocessorProtocol implementation method calls made per-region
- Returns:
- a Map of region names to org.apache.hadoop.hbase.client.coprocessor.Batch.Call.call(Object) return values
- Throws:
- IOException
- Throwable
- */
- Map<byte[], Long> results=table.coprocessorExec(
- RowCountProtocol.class,
- null,
- null,
- new Batch.Call<RowCountProtocol, Long>() {
-
- @Override
- public Long call(RowCountProtocol instance)
- throws IOException {
- // TODO Auto-generated method stub
- return instance.getRowCount();
- }
- }
- );
-
- long total =0;
- //打印出每个region的行数及总行数
- for(Map.Entry<byte[], Long> entry:results.entrySet() ){
- total += entry.getValue();
- System.out.println("Region: "+Bytes.toString(entry.getKey()) +
- ", Count: "+entry.getValue());
- }
-
- System.out.println("Total Count: "+total);
-
-
- } catch (Throwable e) {
- // TODO Auto-generated catch block
- e.printStackTrace();
- }
- }
- }
运行结果如下,可以看出test表共由三个region组成,每个region拥有的行数分别为9,13,78
- 13/01/26 18:59:53 INFO zookeeper.ClientCnxn: Opening socket connection to server master/172.21.15.21:2181. Will not attempt to authenticate using SASL (无法定位登录配置)
- 13/01/26 18:59:53 INFO zookeeper.ClientCnxn: Socket connection established to master/172.21.15.21:2181, initiating session
- 13/01/26 18:59:53 INFO zookeeper.ClientCnxn: Session establishment complete on server master/172.21.15.21:2181, sessionid = 0x13c6a82639f000c, negotiated timeout = 40000
- Region: test,,1358337586380.f3e04b8b43d073a509e9a374f643277a., Count: 9
- Region: test,209,1358337769870.be5a99319eca6f2881ccd73789bfafb0., Count: 13
- Region: test,222,1358337769870.94685f417a95e91d0c9185a95974f866., Count: 78
- Total Count: 100
Batch类提供了一个更方便的方法来获取远程endpoint, Batch.forMethod() ,你可以得到一个配置好的Batch.Call实例用来传递到远程的region servers. 下面对EndPointExample做了修改,看起来是不是好看多了~~
- Batch.Call call =Batch.forMethod(RowCountEndPoint.class, "getKeyValueCount");
-
- Map<byte[], Long> results=table.coprocessorExec(
- RowCountProtocol.class,
- null,
- null,
- call
- );
然而,通过直接implementing Batch.Call 更加灵活和强大,(you can perform additional processing on the results ,implementing Batch.call directly will provide more power and flexibility.) 下面的例子,同时获取rowCount和keyvalueCount
- Map<byte[],Pair<Long,Long>> results=table.coprocessorExec(
- RowCountProtocol.class,
- null,
- null,
- new Batch.Call<RowCountProtocol,Pair<Long,Long>>() {
-
- @Override
- public Pair<Long, Long> call(RowCountProtocol instance)
- throws IOException {
- // TODO Auto-generated method stub
- return new Pair<Long, Long>(
- instance.getRowCount(),
- instance.getKeyValueCount()
- );
- }
- }
- );
-
- //
- long totalRows=0;
- long totalKeyValues=0;
- for(Map.Entry<byte[], Pair<Long,Long>> entry:results.entrySet() ){
-
- totalRows+=entry.getValue().getFirst();
- totalKeyValues+=entry.getValue().getSecond();
-
- System.out.println("region="+Bytes.toString(entry.getKey())+
- " , rowCount="+entry.getValue().getFirst()+
- " , keyValueCount="+entry.getValue().getSecond());
- }
- System.out.println("totalRows="+totalRows+
- ",totalKeyValues="+totalKeyValues);
当然,我们也可以通过coprocessorProxy()方法获取endpoint的client-side 代理,通过该代理,可以在给定的row key所在的region做你想要的操作 (如果row key不存在,则该对应的region为rowkey范围包含该row key的region)。
- RowCountProtocol protocol=table.coprocessorProxy(RowCountProtocol.class, Bytes.toBytes("202"));
-
- long rowsInRegion = protocol.getRowCount();
-
- System.out.println("Region Row Count: "+rowsInRegion);
另一种动态加载方法,通过modifytable修改表方式:
- public static void main(String[] args) throws MasterNotRunningException,
- Exception {
- // TODO Auto-generated method stub
- byte[] tableName = Bytes.toBytes("userinfo");
- Configuration conf = HBaseConfiguration.create();
- HBaseAdmin admin = new HBaseAdmin(conf);
- admin.disableTable(tableName);
-
- HTableDescriptor htd = admin.getTableDescriptor(tableName);
- htd.addCoprocessor(AggregateImplementation.class.getName(), new Path("hdfs://master68:8020/sharelib/aggregate.jar"), 1001, null);
- //htd.removeCoprocessor(RowCountEndpoint.class.getName());
- admin.modifyTable(tableName, htd);
- admin.enableTable(tableName);
- admin.close();
-
- }
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