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