hbase 是什么？
Apache HBase is an open-source, distributed, versioned, non-relational database modeled after Google's Bigtable: A Distributed Storage System for Structured Data by Chang et al. Just as Bigtable leverages the distributed data storage provided by the Google File System, Apache HBase provides Bigtable-like capabilities on top of Hadoop and HDFS.
hbase的应用场景
Use Apache HBase™ when you need random, realtime read/write access to your Big Data. This project's goal is the hosting of very large tables -- billions of rows X millions of columns -- atop clusters of commodity hardware.
hbase的特性
>>>Linear and modular scalability.
>>>Strictly consistent reads and writes.
>>>Automatic and configurable sharding of tables
>>>Automatic failover support between RegionServers.
>>>Convenient base classes for backing Hadoop MapReduce jobs with Apache HBase tables.
>>>Easy to use Java API for client access.
>>>Block cache and Bloom Filters for real-time queries.
>>>Query predicate push down via server side Filters
>>>Thrift gateway and a REST-ful Web service that supports XML, Protobuf, and binary data encoding options
>>>Extensible jruby-based (JIRB) shell
>>>Support for exporting metrics via the Hadoop metrics subsystem to files or Ganglia; or via JMX
hbase 有哪些操作？
先看一下hbase的基本操作：创建一个表，删除一个表，增加一条记录，删除一条记录，遍历一条记录。
import java.io.IOException;
import java.util.ArrayList;
import java.util.List; import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.HColumnDescriptor;
import org.apache.hadoop.hbase.HTableDescriptor;
import org.apache.hadoop.hbase.KeyValue;
import org.apache.hadoop.hbase.MasterNotRunningException;
import org.apache.hadoop.hbase.ZooKeeperConnectionException;
import org.apache.hadoop.hbase.client.Delete;
import org.apache.hadoop.hbase.client.Get;
import org.apache.hadoop.hbase.client.HBaseAdmin;
import org.apache.hadoop.hbase.client.HTable;
import org.apache.hadoop.hbase.client.Result;
import org.apache.hadoop.hbase.client.ResultScanner;
import org.apache.hadoop.hbase.client.Scan;
import org.apache.hadoop.hbase.client.Put;
import org.apache.hadoop.hbase.util.Bytes; public class HBaseTest { private static Configuration conf = null;
/**
* Initialization
*/
static {
conf = HBaseConfiguration.create();
} /**
* Create a table
*/
public static void creatTable(String tableName, String[] familys)
throws Exception {
HBaseAdmin admin = new HBaseAdmin(conf);
if (admin.tableExists(tableName)) {
System.out.println("table already exists!");
} else {
HTableDescriptor tableDesc = new HTableDescriptor(tableName);
for (int i = 0; i < familys.length; i++) {
tableDesc.addFamily(new HColumnDescriptor(familys[i]));
}
admin.createTable(tableDesc);
System.out.println("create table " + tableName + " ok.");
}
} /**
* Delete a table
*/
public static void deleteTable(String tableName) throws Exception {
try {
HBaseAdmin admin = new HBaseAdmin(conf);
admin.disableTable(tableName);
admin.deleteTable(tableName);
System.out.println("delete table " + tableName + " ok.");
} catch (MasterNotRunningException e) {
e.printStackTrace();
} catch (ZooKeeperConnectionException e) {
e.printStackTrace();
}
} /**
* Put (or insert) a row
*/
public static void addRecord(String tableName, String rowKey,
String family, String qualifier, String value) throws Exception {
try {
HTable table = new HTable(conf, tableName);
Put put = new Put(Bytes.toBytes(rowKey));
put.add(Bytes.toBytes(family), Bytes.toBytes(qualifier), Bytes
.toBytes(value));
table.put(put);
System.out.println("insert recored " + rowKey + " to table "
+ tableName + " ok.");
} catch (IOException e) {
e.printStackTrace();
}
} /**
* Delete a row
*/
public static void delRecord(String tableName, String rowKey)
throws IOException {
HTable table = new HTable(conf, tableName);
List<Delete> list = new ArrayList<Delete>();
Delete del = new Delete(rowKey.getBytes());
list.add(del);
table.delete(list);
System.out.println("del recored " + rowKey + " ok.");
} /**
* Get a row
*/
public static void getOneRecord (String tableName, String rowKey) throws IOException{
HTable table = new HTable(conf, tableName);
Get get = new Get(rowKey.getBytes());
Result rs = table.get(get);
for(KeyValue kv : rs.raw()){
System.out.print(new String(kv.getRow()) + " " );
System.out.print(new String(kv.getFamily()) + ":" );
System.out.print(new String(kv.getQualifier()) + " " );
System.out.print(kv.getTimestamp() + " " );
System.out.println(new String(kv.getValue()));
}
}
/**
* Scan (or list) a table
*/
public static void getAllRecord (String tableName) {
try{
HTable table = new HTable(conf, tableName);
Scan s = new Scan();
ResultScanner ss = table.getScanner(s);
for(Result r:ss){
for(KeyValue kv : r.raw()){
System.out.print(new String(kv.getRow()) + " ");
System.out.print(new String(kv.getFamily()) + ":");
System.out.print(new String(kv.getQualifier()) + " ");
System.out.print(kv.getTimestamp() + " ");
System.out.println(new String(kv.getValue()));
}
}
} catch (IOException e){
e.printStackTrace();
}
} public static void main(String[] agrs) {
try {
String tablename = "scores";
String[] familys = { "grade", "course" };
HBaseTest.creatTable(tablename, familys); // add record zkb
HBaseTest.addRecord(tablename, "zkb", "grade", "", "5");
HBaseTest.addRecord(tablename, "zkb", "course", "", "90");
HBaseTest.addRecord(tablename, "zkb", "course", "math", "97");
HBaseTest.addRecord(tablename, "zkb", "course", "art", "87");
// add record baoniu
HBaseTest.addRecord(tablename, "baoniu", "grade", "", "4");
HBaseTest.addRecord(tablename, "baoniu", "course", "math", "89"); System.out.println("===========get one record========");
HBaseTest.getOneRecord(tablename, "zkb"); System.out.println("===========show all record========");
HBaseTest.getAllRecord(tablename); System.out.println("===========del one record========");
HBaseTest.delRecord(tablename, "baoniu");
HBaseTest.getAllRecord(tablename); System.out.println("===========show all record========");
HBaseTest.getAllRecord(tablename);
} catch (Exception e) {
e.printStackTrace();
}
}
}
基本概念
HTable
核心概念，实现了Table，用来和hbase的一个单表进行通信。轻量级的，提供获取和关闭方法。
这个类不能通过构造函数直接构建出来。可以通过Connection获取该类的一个实例。参考ConnectionFactory类生成实例：
Connection connection = ConnectionFactory.createConnection(config);
Table table = connection.getTable(TableName.valueOf("table1"));
try {
// Use the table as needed, for a single operation and a single thread
} finally {
table.close();
connection.close();
}
Htable的字段有哪些呢？
public class HTable implements HTableInterface, RegionLocator {
private static final Log LOG = LogFactory.getLog(HTable.class);
protected ClusterConnection connection;
private final TableName tableName;
private volatile Configuration configuration;
private TableConfiguration tableConfiguration;
protected BufferedMutatorImpl mutator;
private boolean autoFlush = true;
private boolean closed = false;
protected int scannerCaching;
private ExecutorService pool; // For Multi & Scan
private int operationTimeout;
private final boolean cleanupPoolOnClose; // shutdown the pool in close()
private final boolean cleanupConnectionOnClose; // close the connection in close()
private Consistency defaultConsistency = Consistency.STRONG;
/** The Async process for batch */
protected AsyncProcess multiAp;
private RpcRetryingCallerFactory rpcCallerFactory;
private RpcControllerFactory rpcControllerFactory;
}
HTableDescriptor包含了HBase表的详细信息，例如所有列家族的描述，该表是否一个分类表，ROOT或者hbase:meta，该表是否只读，当region分片时memstore的最大值，关联的coprocessor等等。
Htable继承并实现了Table，Table用来和一个hbase单表进行通信，从表中获取，插入，删除或者扫描数据。使用Connection来获取Table实例，使用完毕后调用close()方法。
Htable也继承实现了RegionLocator，RegionLocator用来定位一张Hbase单表的区域位置信息，可以通过Connection获取该类的实例，RegionLocator的getRegionLocation方法返回HRegionLocation。
HRegionLocation
记录HRegionInfo和HRegionServer的主机地址的数据结构。
构造函数：
public HRegionLocation(HRegionInfo regionInfo, ServerName serverName) {
this(regionInfo, serverName, HConstants.NO_SEQNUM);
}
public HRegionLocation(HRegionInfo regionInfo, ServerName serverName, long seqNum) {
this.regionInfo = regionInfo;
this.serverName = serverName;
this.seqNum = seqNum;
}
HRegionInfo
一个区域的信息。区域是在一张表的整个键空间中一系列的键，一个标识(时间戳)区分不同子序列(在区间分隔之后)，一个复制ID区分同一序列和同一区域状态信息的不同实例。
一个区域有一个位于的名称，名称由下列的字段组成：
表名(tableName)：表的名称。
开始键(startKey)：一个区间的开始键。
区域ID(regionId)：创建区域的时间戳。
复制ID(replicaId)：一个区分同一区域序列的Id，从0开始，保存到不同的服务器，同一个区域的序列可以保存在多个位置中。
加密后的名称(encodedName):md5加密后的区域名称。
除了区域名称外，区域信息还包含：
结束键(endkey):区域的结束键(独有的)
分片(split)：区域是否分片
离线(offline)：区域是否离线
在0.98版本或者之前，一组表的区域会完全包含所有的键空间，在任何时间点，一个行键通常属于一个单独的区域，该单独区域又属于一个单独的服务器。在0.99+版本，一个区域可以有多个实例（叫做备份），因此一行可以对应多个HRegionInfo。这些HRI除了备份Id字段外都可以共用字段。若备份Id未设置，默认为0。
/**
* The new format for a region name contains its encodedName at the end.
* The encoded name also serves as the directory name for the region
* in the filesystem.
*
* New region name format:
* <tablename>,,<startkey>,<regionIdTimestamp>.<encodedName>.
* where,
* <encodedName> is a hex version of the MD5 hash of
* <tablename>,<startkey>,<regionIdTimestamp>
*
* The old region name format:
* <tablename>,<startkey>,<regionIdTimestamp>
* For region names in the old format, the encoded name is a 32-bit
* JenkinsHash integer value (in its decimal notation, string form).
*<p>
* **NOTE**
*
* The first hbase:meta region, and regions created by an older
* version of HBase (0.20 or prior) will continue to use the
* old region name format.
*/ /** Separator used to demarcate the encodedName in a region name
* in the new format. See description on new format above.
*/
private static final int ENC_SEPARATOR = '.';
public static final int MD5_HEX_LENGTH = 32; /** A non-capture group so that this can be embedded. */
public static final String ENCODED_REGION_NAME_REGEX = "(?:[a-f0-9]+)"; // to keep appended int's sorted in string format. Only allows 2 bytes to be
// sorted for replicaId
public static final String REPLICA_ID_FORMAT = "%04X"; public static final byte REPLICA_ID_DELIMITER = (byte)'_'; private static final int MAX_REPLICA_ID = 0xFFFF;
static final int DEFAULT_REPLICA_ID = 0; private byte [] endKey = HConstants.EMPTY_BYTE_ARRAY;
// This flag is in the parent of a split while the parent is still referenced
// by daughter regions. We USED to set this flag when we disabled a table
// but now table state is kept up in zookeeper as of 0.90.0 HBase.
private boolean offLine = false;
private long regionId = -1;
private transient byte [] regionName = HConstants.EMPTY_BYTE_ARRAY;
private boolean split = false;
private byte [] startKey = HConstants.EMPTY_BYTE_ARRAY;
private int hashCode = -1;
//TODO: Move NO_HASH to HStoreFile which is really the only place it is used.
public static final String NO_HASH = null;
private String encodedName = null;
private byte [] encodedNameAsBytes = null;
private int replicaId = DEFAULT_REPLICA_ID; // Current TableName
private TableName tableName = null; /** HRegionInfo for first meta region */
public static final HRegionInfo FIRST_META_REGIONINFO =
new HRegionInfo(1L, TableName.META_TABLE_NAME);
先了解一下HBase的数据结构：
组成部件说明：
Row Key： Table主键 行键 Table中记录按照Row Key排序
Timestamp： 每次对数据操作对应的时间戳，也即数据的version number
Column Family： 列簇，一个table在水平方向有一个或者多个列簇，列簇可由任意多个Column组成，列簇支持动态扩展，无须预定义数量及类型，二进制存储，用户需自行进行类型转换。
行操作
Get用来对一个单独的行进行Get操作：
获取一个row的所有信息前，需要实例化一个Get对象。
获取特定家族的所有列，使用addFamily(byte[])。
获取特定列，使用addColumn(byte[], byte[])
获取在特定的时间戳内的一系列列，使用setTimeRange(long, long)
获取在特定时间戳的列，使用setTimeStamp(long)
限制返回的列数，使用setMaxVersions(int)
增加过滤器，使用setFilter(Filter)。 Put用来对一个单独的列进行Put操作：
使用Put前需初始化Put对象，来插入一行使用add(byte[], byte[], byte[])，若设定时间戳则使用add(byte[], byte[], long, byte[])。 Append 操作：
对一行增加多个列，使用add(byte[], byte[], byte[])；
参考文献：
【1】http://hbase.apache.org/
【2】https://autofei.wordpress.com/2012/04/02/java-example-code-using-hbase-data-model-operations/
【3】http://www.cnblogs.com/shitouer/archive/2012/06/04/2533518.html