HBase - Quick Guide

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HBase - Overview

Since 1970, RDBMS is the solution for data storage and maintenance related problems. After the advent of big data, companies realized the benefit of processing big data and started opting for solutions like Hadoop.

Hadoop uses distributed file system for storing big data, and MapReduce to process it. Hadoop excels in storing and processing of huge data of various formats such as arbitrary, semi-, or even unstructured.

Limitations of Hadoop

Hadoop can perform only batch processing, and data will be accessed only in a sequential manner. That means one has to search the entire dataset even for the simplest of jobs.

A huge dataset when processed results in another huge data set, which should also be processed sequentially. At this point, a new solution is needed to access any point of data in a single unit of time (random access).

Hadoop Random Access Databases

Applications such as HBase, Cassandra, couchDB, Dynamo, and MongoDB are some of the databases that store huge amounts of data and access the data in a random manner.

What is HBase?

HBase is a distributed column-oriented database built on top of the Hadoop file system. It is an open-source project and is horizontally scalable.

HBase is a data model that is similar to Google’s big table designed to provide quick random access to huge amounts of structured data. It leverages the fault tolerance provided by the Hadoop File System (HDFS).

It is a part of the Hadoop ecosystem that provides random real-time read/write access to data in the Hadoop File System.

One can store the data in HDFS either directly or through HBase. Data consumer reads/accesses the data in HDFS randomly using HBase. HBase sits on top of the Hadoop File System and provides read and write access.

HBase and HDFS

HDFS	HBase
HDFS is a distributed file system suitable for storing large files.	HBase is a database built on top of the HDFS.
HDFS does not support fast individual record lookups.	HBase provides fast lookups for larger tables.
It provides high latency batch processing; no concept of batch processing.	It provides low latency access to single rows from billions of records (Random access).
It provides only sequential access of data.	HBase internally uses Hash tables and provides random access, and it stores the data in indexed HDFS files for faster lookups.

Storage Mechanism in HBase

HBase is a column-oriented database and the tables in it are sorted by row. The table schema defines only column families, which are the key value pairs. A table have multiple column families and each column family can have any number of columns. Subsequent column values are stored contiguously on the disk. Each cell value of the table has a timestamp. In short, in an HBase:

• Table is a collection of rows.
• Row is a collection of column families.
• Column family is a collection of columns.
• Column is a collection of key value pairs.

Given below is an example schema of table in HBase.

Rowid	Column Family			Column Family			Column Family			Column Family
	col1	col2	col3	col1	col2	col3	col1	col2	col3	col1	col2	col3
1
2
3

Column Oriented and Row Oriented

Column-oriented databases are those that store data tables as sections of columns of data, rather than as rows of data. Shortly, they will have column families.

Row-Oriented Database	Column-Oriented Database
It is suitable for Online Transaction Process (OLTP).	It is suitable for Online Analytical Processing (OLAP).
Such databases are designed for small number of rows and columns.	Column-oriented databases are designed for huge tables.

The following image shows column families in a column-oriented database:

HBase and RDBMS

HBase	RDBMS
HBase is schema-less, it doesn't have the concept of fixed columns schema; defines only column families.	An RDBMS is governed by its schema, which describes the whole structure of tables.
It is built for wide tables. HBase is horizontally scalable.	It is thin and built for small tables. Hard to scale.
No transactions are there in HBase.	RDBMS is transactional.
It has de-normalized data.	It will have normalized data.
It is good for semi-structured as well as structured data.	It is good for structured data.

Features of HBase

• HBase is linearly scalable.
• It has automatic failure support.
• It provides consistent read and writes.
• It integrates with Hadoop, both as a source and a destination.
• It has easy java API for client.
• It provides data replication across clusters.

Where to Use HBase

• Apache HBase is used to have random, real-time read/write access to Big Data.

• It hosts very large tables on top of clusters of commodity hardware.

• Apache HBase is a non-relational database modeled after Google's Bigtable. Bigtable acts up on Google File System, likewise Apache HBase works on top of Hadoop and HDFS.

Applications of HBase

• It is used whenever there is a need to write heavy applications.
• HBase is used whenever we need to provide fast random access to available data.
• Companies such as Facebook, Twitter, Yahoo, and Adobe use HBase internally.

HBase History

Year	Event
Nov 2006	Google released the paper on BigTable.
Feb 2007	Initial HBase prototype was created as a Hadoop contribution.
Oct 2007	The first usable HBase along with Hadoop 0.15.0 was released.
Jan 2008	HBase became the sub project of Hadoop.
Oct 2008	HBase 0.18.1 was released.
Jan 2009	HBase 0.19.0 was released.
Sept 2009	HBase 0.20.0 was released.
May 2010	HBase became Apache top-level project.

HBase - Architecture

In HBase, tables are split into regions and are served by the region servers. Regions are vertically divided by column families into “Stores”. Stores are saved as files in HDFS. Shown below is the architecture of HBase.

Note: The term ‘store’ is used for regions to explain the storage structure.

HBase has three major components: the client library, a master server, and region servers. Region servers can be added or removed as per requirement.

MasterServer

The master server -

• Assigns regions to the region servers and takes the help of Apache ZooKeeper for this task.

• Handles load balancing of the regions across region servers. It unloads the busy servers and shifts the regions to less occupied servers.

• Maintains the state of the cluster by negotiating the load balancing.

• Is responsible for schema changes and other metadata operations such as creation of tables and column families.

Regions

Regions are nothing but tables that are split up and spread across the region servers.

Region server

The region servers have regions that -

• Communicate with the client and handle data-related operations.
• Handle read and write requests for all the regions under it.
• Decide the size of the region by following the region size thresholds.

When we take a deeper look into the region server, it contain regions and stores as shown below:

The store contains memory store and HFiles. Memstore is just like a cache memory. Anything that is entered into the HBase is stored here initially. Later, the data is transferred and saved in Hfiles as blocks and the memstore is flushed.

Zookeeper

• Zookeeper is an open-source project that provides services like maintaining configuration information, naming, providing distributed synchronization, etc.

• Zookeeper has ephemeral nodes representing different region servers. Master servers use these nodes to discover available servers.

• In addition to availability, the nodes are also used to track server failures or network partitions.

• Clients communicate with region servers via zookeeper.

• In pseudo and standalone modes, HBase itself will take care of zookeeper.

HBase - Installation

This chapter explains how HBase is installed and initially configured. Java and Hadoop are required to proceed with HBase, so you have to download and install java and Hadoop in your system.

Pre-Installation Setup

Before installing Hadoop into Linux environment, we need to set up Linux using ssh (Secure Shell). Follow the steps given below for setting up the Linux environment.

Creating a User

First of all, it is recommended to create a separate user for Hadoop to isolate the Hadoop file system from the Unix file system. Follow the steps given below to create a user.

• Open the root using the command “su”.
• Create a user from the root account using the command “useradd username”.
• Now you can open an existing user account using the command “su username”.

Open the Linux terminal and type the following commands to create a user.

$ su
password:
# useradd hadoop
# passwd hadoop
New passwd:
Retype new passwd

SSH Setup and Key Generation

SSH setup is required to perform different operations on the cluster such as start, stop, and distributed daemon shell operations. To authenticate different users of Hadoop, it is required to provide public/private key pair for a Hadoop user and share it with different users.

The following commands are used to generate a key value pair using SSH. Copy the public keys form id_rsa.pub to authorized_keys, and provide owner, read and write permissions to authorized_keys file respectively.

$ ssh-keygen -t rsa
$ cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys
$ chmod 0600 ~/.ssh/authorized_keys

Verify ssh

ssh localhost

Installing Java

Java is the main prerequisite for Hadoop and HBase. First of all, you should verify the existence of java in your system using “java -version”. The syntax of java version command is given below.

$ java -version

If everything works fine, it will give you the following output.

java version "1.7.0_71"
Java(TM) SE Runtime Environment (build 1.7.0_71-b13)
Java HotSpot(TM) Client VM (build 25.0-b02, mixed mode)

If java is not installed in your system, then follow the steps given below for installing java.

Step 1

Download java (JDK <latest version> - X64.tar.gz) by visiting the following link Oracle Java.

Then jdk-7u71-linux-x64.tar.gz will be downloaded into your system.

Step 2

Generally you will find the downloaded java file in Downloads folder. Verify it and extract the jdk-7u71-linux-x64.gz file using the following commands.

$ cd Downloads/
$ ls
jdk-7u71-linux-x64.gz

$ tar zxf jdk-7u71-linux-x64.gz
$ ls
jdk1.7.0_71 jdk-7u71-linux-x64.gz

Step 3

To make java available to all the users, you have to move it to the location “/usr/local/”. Open root and type the following commands.

$ su
password:
# mv jdk1.7.0_71 /usr/local/
# exit

Step 4

For setting up PATH and JAVA_HOME variables, add the following commands to ~/.bashrc file.

export JAVA_HOME=/usr/local/jdk1.7.0_71
export PATH= $PATH:$JAVA_HOME/bin

Now apply all the changes into the current running system.

$ source ~/.bashrc

Step 5

Use the following commands to configure java alternatives:

# alternatives --install /usr/bin/java java usr/local/java/bin/java 2

# alternatives --install /usr/bin/javac javac usr/local/java/bin/javac 2

# alternatives --install /usr/bin/jar jar usr/local/java/bin/jar 2


# alternatives --set java usr/local/java/bin/java

# alternatives --set javac usr/local/java/bin/javac

# alternatives --set jar usr/local/java/bin/jar

Now verify the java -version command from the terminal as explained above.

Downloading Hadoop

After installing java, you have to install Hadoop. First of all, verify the existence of Hadoop using “ Hadoop version ” command as shown below.

hadoop version

If everything works fine, it will give you the following output.

Hadoop 2.6.0
Compiled by jenkins on 2014-11-13T21:10Z
Compiled with protoc 2.5.0
From source with checksum 18e43357c8f927c0695f1e9522859d6a
This command was run using
/home/hadoop/hadoop/share/hadoop/common/hadoop-common-2.6.0.jar

If your system is unable to locate Hadoop, then download Hadoop in your system. Follow the commands given below to do so.

Download and extract hadoop-2.6.0 from Apache Software Foundation using the following commands.

$ su
password:
# cd /usr/local
# wget http://mirrors.advancedhosters.com/apache/hadoop/common/hadoop-
2.6.0/hadoop-2.6.0-src.tar.gz
# tar xzf hadoop-2.6.0-src.tar.gz
# mv hadoop-2.6.0/* hadoop/
# exit

Installing Hadoop

Install Hadoop in any of the required mode. Here, we are demonstrating HBase functionalities in pseudo distributed mode, therefore install Hadoop in pseudo distributed mode.

The following steps are used for installing Hadoop 2.4.1.

Step 1 - Setting up Hadoop

You can set Hadoop environment variables by appending the following commands to ~/.bashrc file.

export HADOOP_HOME=/usr/local/hadoop
export HADOOP_MAPRED_HOME=$HADOOP_HOME
export HADOOP_COMMON_HOME=$HADOOP_HOME
export HADOOP_HDFS_HOME=$HADOOP_HOME
export YARN_HOME=$HADOOP_HOME
export HADOOP_COMMON_LIB_NATIVE_DIR=$HADOOP_HOME/lib/native
export PATH=$PATH:$HADOOP_HOME/sbin:$HADOOP_HOME/bin
export HADOOP_INSTALL=$HADOOP_HOME

Now apply all the changes into the current running system.

$ source ~/.bashrc

Step 2 - Hadoop Configuration

You can find all the Hadoop configuration files in the location “$HADOOP_HOME/etc/hadoop”. You need to make changes in those configuration files according to your Hadoop infrastructure.

$ cd $HADOOP_HOME/etc/hadoop

In order to develop Hadoop programs in java, you have to reset the java environment variable in hadoop-env.sh file by replacing JAVA_HOME value with the location of java in your system.

export JAVA_HOME=/usr/local/jdk1.7.0_71

You will have to edit the following files to configure Hadoop.

core-site.xml

The core-site.xml file contains information such as the port number used for Hadoop instance, memory allocated for file system, memory limit for storing data, and the size of Read/Write buffers.

Open core-site.xml and add the following properties in between the <configuration> and </configuration> tags.

<configuration>
   <property>
      <name>fs.default.name</name>
      <value>hdfs://localhost:9000</value>
   </property>
</configuration>

hdfs-site.xml

The hdfs-site.xml file contains information such as the value of replication data, namenode path, and datanode path of your local file systems, where you want to store the Hadoop infrastructure.

Let us assume the following data.

dfs.replication (data replication value) = 1
(In the below given path /hadoop/ is the user name.
hadoopinfra/hdfs/namenode is the directory created by hdfs file system.)

namenode path = //home/hadoop/hadoopinfra/hdfs/namenode
(hadoopinfra/hdfs/datanode is the directory created by hdfs file system.)

datanode path = //home/hadoop/hadoopinfra/hdfs/datanode

Open this file and add the following properties in between the <configuration>, </configuration> tags.

<configuration>
   <property>
      <name>dfs.replication</name >
      <value>1</value>
   </property>
	
   <property>
      <name>dfs.name.dir</name>
      <value>file:///home/hadoop/hadoopinfra/hdfs/namenode</value>
   </property>
	
   <property>
      <name>dfs.data.dir</name>
      <value>file:///home/hadoop/hadoopinfra/hdfs/datanode</value>
   </property>
</configuration>

Note: In the above file, all the property values are user-defined and you can make changes according to your Hadoop infrastructure.

yarn-site.xml

This file is used to configure yarn into Hadoop. Open the yarn-site.xml file and add the following property in between the <configuration$gt;, </configuration$gt; tags in this file.

<configuration>
   <property>
      <name>yarn.nodemanager.aux-services</name>
      <value>mapreduce_shuffle</value>
   </property>
</configuration>

mapred-site.xml

This file is used to specify which MapReduce framework we are using. By default, Hadoop contains a template of yarn-site.xml. First of all, it is required to copy the file from mapred-site.xml.template to mapred-site.xml file using the following command.

$ cp mapred-site.xml.template mapred-site.xml

Open mapred-site.xml file and add the following properties in between the <configuration> and </configuration> tags.

<configuration>
   <property>
      <name>mapreduce.framework.name</name>
      <value>yarn</value>
   </property>
</configuration>

Verifying Hadoop Installation

The following steps are used to verify the Hadoop installation.

Step 1 - Name Node Setup

Set up the namenode using the command “hdfs namenode -format” as follows.

$ cd ~
$ hdfs namenode -format

The expected result is as follows.

10/24/14 21:30:55 INFO namenode.NameNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting NameNode
STARTUP_MSG: host = localhost/192.168.1.11
STARTUP_MSG: args = [-format]
STARTUP_MSG: version = 2.4.1
...
...
10/24/14 21:30:56 INFO common.Storage: Storage directory
/home/hadoop/hadoopinfra/hdfs/namenode has been successfully formatted.
10/24/14 21:30:56 INFO namenode.NNStorageRetentionManager: Going to
retain 1 images with txid >= 0
10/24/14 21:30:56 INFO util.ExitUtil: Exiting with status 0
10/24/14 21:30:56 INFO namenode.NameNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down NameNode at localhost/192.168.1.11
************************************************************/

Step 2 - Verifying Hadoop dfs

The following command is used to start dfs. Executing this command will start your Hadoop file system.

$ start-dfs.sh

The expected output is as follows.

10/24/14 21:37:56
Starting namenodes on [localhost]
localhost: starting namenode, logging to /home/hadoop/hadoop-
2.4.1/logs/hadoop-hadoop-namenode-localhost.out
localhost: starting datanode, logging to /home/hadoop/hadoop-
2.4.1/logs/hadoop-hadoop-datanode-localhost.out
Starting secondary namenodes [0.0.0.0]

Step 3 - Verifying Yarn Script

The following command is used to start the yarn script. Executing this command will start your yarn daemons.

$ start-yarn.sh

The expected output is as follows.

starting yarn daemons
starting resourcemanager, logging to /home/hadoop/hadoop-
2.4.1/logs/yarn-hadoop-resourcemanager-localhost.out
localhost: starting nodemanager, logging to /home/hadoop/hadoop-
2.4.1/logs/yarn-hadoop-nodemanager-localhost.out

Step 4 - Accessing Hadoop on Browser

The default port number to access Hadoop is 50070. Use the following url to get Hadoop services on your browser.

http://localhost:50070

Step 5 - Verify all Applications of Cluster

The default port number to access all the applications of cluster is 8088. Use the following url to visit this service.

http://localhost:8088/

Installing HBase

We can install HBase in any of the three modes: Standalone mode, Pseudo Distributed mode, and Fully Distributed mode.

Installing HBase in Standalone Mode

Download the latest stable version of HBase form http://www.interior-dsgn.com/apache/hbase/stable/ using “wget” command, and extract it using the tar “zxvf” command. See the following command.

$cd usr/local/
$wget http://www.interior-dsgn.com/apache/hbase/stable/hbase-0.98.8-
hadoop2-bin.tar.gz
$tar -zxvf hbase-0.98.8-hadoop2-bin.tar.gz

Shift to super user mode and move the HBase folder to /usr/local as shown below.

$su
$password: enter your password here
mv hbase-0.99.1/* Hbase/

Configuring HBase in Standalone Mode

Before proceeding with HBase, you have to edit the following files and configure HBase.

hbase-env.sh

Set the java Home for HBase and open hbase-env.sh file from the conf folder. Edit JAVA_HOME environment variable and change the existing path to your current JAVA_HOME variable as shown below.

cd /usr/local/Hbase/conf
gedit hbase-env.sh

This will open the env.sh file of HBase. Now replace the existing JAVA_HOME value with your current value as shown below.

export JAVA_HOME=/usr/lib/jvm/java-1.7.0

hbase-site.xml

This is the main configuration file of HBase. Set the data directory to an appropriate location by opening the HBase home folder in /usr/local/HBase. Inside the conf folder, you will find several files, open the hbase-site.xml file as shown below.

#cd /usr/local/HBase/
#cd conf
# gedit hbase-site.xml

Inside the hbase-site.xml file, you will find the <configuration> and </configuration> tags. Within them, set the HBase directory under the property key with the name “hbase.rootdir” as shown below.

<configuration>
   //Here you have to set the path where you want HBase to store its files.
   <property>
      <name>hbase.rootdir</name>
      <value>file:/home/hadoop/HBase/HFiles</value>
   </property>
	
   //Here you have to set the path where you want HBase to store its built in zookeeper  files.
   <property>
      <name>hbase.zookeeper.property.dataDir</name>
      <value>/home/hadoop/zookeeper</value>
   </property>
</configuration>

With this, the HBase installation and configuration part is successfully complete. We can start HBase by using start-hbase.sh script provided in the bin folder of HBase. For that, open HBase Home Folder and run HBase start script as shown below.

$cd /usr/local/HBase/bin
$./start-hbase.sh

If everything goes well, when you try to run HBase start script, it will prompt you a message saying that HBase has started.

starting master, logging to /usr/local/HBase/bin/../logs/hbase-tpmaster-localhost.localdomain.out

Installing HBase in Pseudo-Distributed Mode

Let us now check how HBase is installed in pseudo-distributed mode.

Configuring HBase

Before proceeding with HBase, configure Hadoop and HDFS on your local system or on a remote system and make sure they are running. Stop HBase if it is running.

hbase-site.xml

Edit hbase-site.xml file to add the following properties.

<property>
   <name>hbase.cluster.distributed</name>
   <value>true</value>
</property>

It will mention in which mode HBase should be run. In the same file from the local file system, change the hbase.rootdir, your HDFS instance address, using the hdfs://// URI syntax. We are running HDFS on the localhost at port 8030.

<property>
   <name>hbase.rootdir</name>
   <value>hdfs://localhost:8030/hbase</value>
</property>

Starting HBase

After configuration is over, browse to HBase home folder and start HBase using the following command.

$cd /usr/local/HBase
$bin/start-hbase.sh

Note: Before starting HBase, make sure Hadoop is running.

Checking the HBase Directory in HDFS

HBase creates its directory in HDFS. To see the created directory, browse to Hadoop bin and type the following command.

$ ./bin/hadoop fs -ls /hbase

If everything goes well, it will give you the following output.

Found 7 items
drwxr-xr-x - hbase users 0 2014-06-25 18:58 /hbase/.tmp
drwxr-xr-x - hbase users 0 2014-06-25 21:49 /hbase/WALs
drwxr-xr-x - hbase users 0 2014-06-25 18:48 /hbase/corrupt
drwxr-xr-x - hbase users 0 2014-06-25 18:58 /hbase/data
-rw-r--r-- 3 hbase users 42 2014-06-25 18:41 /hbase/hbase.id
-rw-r--r-- 3 hbase users 7 2014-06-25 18:41 /hbase/hbase.version
drwxr-xr-x - hbase users 0 2014-06-25 21:49 /hbase/oldWALs

Starting and Stopping a Master

Using the “local-master-backup.sh” you can start up to 10 servers. Open the home folder of HBase, master and execute the following command to start it.

$ ./bin/local-master-backup.sh 2 4

To kill a backup master, you need its process id, which will be stored in a file named “/tmp/hbase-USER-X-master.pid.” you can kill the backup master using the following command.

$ cat /tmp/hbase-user-1-master.pid |xargs kill -9

Starting and Stopping RegionServers

You can run multiple region servers from a single system using the following command.

$ .bin/local-regionservers.sh start 2 3

To stop a region server, use the following command.

$ .bin/local-regionservers.sh stop 3

 

Starting HBaseShell

After Installing HBase successfully, you can start HBase Shell. Below given are the sequence of steps that are to be followed to start the HBase shell. Open the terminal, and login as super user.

Start Hadoop File System

Browse through Hadoop home sbin folder and start Hadoop file system as shown below.

$cd $HADOOP_HOME/sbin
$start-all.sh

Start HBase

Browse through the HBase root directory bin folder and start HBase.

$cd /usr/local/HBase
$./bin/start-hbase.sh

Start HBase Master Server

This will be the same directory. Start it as shown below.

$./bin/local-master-backup.sh start 2 (number signifies specific
server.) 

Start Region

Start the region server as shown below.

$./bin/./local-regionservers.sh start 3

Start HBase Shell

You can start HBase shell using the following command.

$cd bin
$./hbase shell

This will give you the HBase Shell Prompt as shown below.

2014-12-09 14:24:27,526 INFO [main] Configuration.deprecation:
hadoop.native.lib is deprecated. Instead, use io.native.lib.available
HBase Shell; enter 'help<RETURN>' for list of supported commands.
Type "exit<RETURN>" to leave the HBase Shell
Version 0.98.8-hadoop2, r6cfc8d064754251365e070a10a82eb169956d5fe, Fri
Nov 14 18:26:29 PST 2014

hbase(main):001:0>

HBase Web Interface

To access the web interface of HBase, type the following url in the browser.

http://localhost:60010

This interface lists your currently running Region servers, backup masters and HBase tables.

HBase Region servers and Backup Masters

HBase Tables

Setting Java Environment

We can also communicate with HBase using Java libraries, but before accessing HBase using Java API you need to set classpath for those libraries.

Setting the Classpath

Before proceeding with programming, set the classpath to HBase libraries in .bashrc file. Open .bashrc in any of the editors as shown below.

$ gedit ~/.bashrc

Set classpath for HBase libraries (lib folder in HBase) in it as shown below.

export CLASSPATH = $CLASSPATH://home/hadoop/hbase/lib/*

This is to prevent the “class not found” exception while accessing the HBase using java API.

HBase - Shell

This chapter explains how to start HBase interactive shell that comes along with HBase.

HBase Shell

HBase contains a shell using which you can communicate with HBase. HBase uses the Hadoop File System to store its data. It will have a master server and region servers. The data storage will be in the form of regions (tables). These regions will be split up and stored in region servers.

The master server manages these region servers and all these tasks take place on HDFS. Given below are some of the commands supported by HBase Shell.

General Commands

• status - Provides the status of HBase, for example, the number of servers.

• version - Provides the version of HBase being used.

• table_help - Provides help for table-reference commands.

• whoami - Provides information about the user.

Data Definition Language

These are the commands that operate on the tables in HBase.

• create - Creates a table.

• list - Lists all the tables in HBase.

• disable - Disables a table.

• is_disabled - Verifies whether a table is disabled.

• enable - Enables a table.

• is_enabled - Verifies whether a table is enabled.

• describe - Provides the description of a table.

• alter - Alters a table.

• exists - Verifies whether a table exists.

• drop - Drops a table from HBase.

• drop_all - Drops the tables matching the ‘regex’ given in the command.

• Java Admin API - Prior to all the above commands, Java provides an Admin API to achieve DDL functionalities through programming. Under org.apache.hadoop.hbase.client package, HBaseAdmin and HTableDescriptor are the two important classes in this package that provide DDL functionalities.

Data Manipulation Language

• put - Puts a cell value at a specified column in a specified row in a particular table.

• get - Fetches the contents of row or a cell.

• delete - Deletes a cell value in a table.

• deleteall - Deletes all the cells in a given row.

• scan - Scans and returns the table data.

• count - Counts and returns the number of rows in a table.

• truncate - Disables, drops, and recreates a specified table.

• Java client API - Prior to all the above commands, Java provides a client API to achieve DML functionalities, CRUD (Create Retrieve Update Delete) operations and more through programming, under org.apache.hadoop.hbase.client package. HTable Put and Get are the important classes in this package.

Starting HBase Shell

To access the HBase shell, you have to navigate to the HBase home folder.

cd /usr/localhost/
cd Hbase

You can start the HBase interactive shell using “hbase shell” command as shown below.

./bin/hbase shell

If you have successfully installed HBase in your system, then it gives you the HBase shell prompt as shown below.

HBase Shell; enter 'help<RETURN>' for list of supported commands.
Type "exit<RETURN>" to leave the HBase Shell
Version 0.94.23, rf42302b28aceaab773b15f234aa8718fff7eea3c, Wed Aug 27
00:54:09 UTC 2014

hbase(main):001:0>

To exit the interactive shell command at any moment, type exit or use <ctrl+c>. Check the shell functioning before proceeding further. Use the list command for this purpose. List is a command used to get the list of all the tables in HBase. First of all, verify the installation and the configuration of HBase in your system using this command as shown below.

hbase(main):001:0> list

When you type this command, it gives you the following output.

hbase(main):001:0> list
TABLE

HBase - General Commands

The general commands in HBase are status, version, table_help, and whoami. This chapter explains these commands.

status

This command returns the status of the system including the details of the servers running on the system. Its syntax is as follows:

hbase(main):009:0> status

If you execute this command, it returns the following output.

hbase(main):009:0> status
3 servers, 0 dead, 1.3333 average load

version

This command returns the version of HBase used in your system. Its syntax is as follows:

hbase(main):010:0> version

If you execute this command, it returns the following output.

hbase(main):009:0> version
0.98.8-hadoop2, r6cfc8d064754251365e070a10a82eb169956d5fe, Fri Nov 14
18:26:29 PST 2014

table_help

This command guides you what and how to use table-referenced commands. Given below is the syntax to use this command.

hbase(main):02:0> table_help

When you use this command, it shows help topics for table-related commands. Given below is the partial output of this command.

hbase(main):002:0> table_help
Help for table-reference commands.
You can either create a table via 'create' and then manipulate the table
via commands like 'put', 'get', etc.
See the standard help information for how to use each of these commands.
However, as of 0.96, you can also get a reference to a table, on which
you can invoke commands.
For instance, you can get create a table and keep around a reference to
it via:
 hbase> t = create 't', 'cf'…...

whoami

This command returns the user details of HBase. If you execute this command, returns the current HBase user as shown below.

hbase(main):008:0> whoami
hadoop (auth:SIMPLE)
groups: hadoop

HBase - Admin API

HBase is written in java, therefore it provides java API to communicate with HBase. Java API is the fastest way to communicate with HBase. Given below is the referenced java Admin API that covers the tasks used to manage tables.

Class HBaseAdmin

HBaseAdmin is a class representing the Admin. This class belongs to the org.apache.hadoop.hbase.client package. Using this class, you can perform the tasks of an administrator. You can get the instance of Admin using Connection.getAdmin() method.

Methods and Description

S.No.	Methods and Description
1	void createTable(HTableDescriptor desc) Creates a new table.
2	void createTable(HTableDescriptor desc, byte[][] splitKeys) Creates a new table with an initial set of empty regions defined by the specified split keys.
3	void deleteColumn(byte[] tableName, String columnName) Deletes a column from a table.
4	void deleteColumn(String tableName, String columnName) Delete a column from a table.
5	void deleteTable(String tableName) Deletes a table.

Class Descriptor

This class contains the details about an HBase table such as:

• the descriptors of all the column families,
• if the table is a catalog table,
• if the table is read only,
• the maximum size of the mem store,
• when the region split should occur,
• co-processors associated with it, etc.

Constructors

S.No.	Constructor and summary
1	HTableDescriptor(TableName name) Constructs a table descriptor specifying a TableName object.

Methods and Description

S.No.	Methods and Description
1	HTableDescriptor addFamily(HColumnDescriptor family) Adds a column family to the given descriptor

HBase - Create Table

Creating a Table using HBase Shell

You can create a table using the create command, here you must specify the table name and the Column Family name. The syntax to create a table in HBase shell is shown below.

create ‘<table name>’,’<column family>’ 

Example

Given below is a sample schema of a table named emp. It has two column families: “personal data” and “professional data”.

Row key	personal data	professional data

You can create this table in HBase shell as shown below.

hbase(main):002:0> create 'emp', 'personal data', 'professional data'

And it will give you the following output.

0 row(s) in 1.1300 seconds
=> Hbase::Table - emp

Verification

You can verify whether the table is created using the list command as shown below. Here you can observe the created emp table.

hbase(main):002:0> list
TABLE 
emp
2 row(s) in 0.0340 seconds

Creating a Table Using java API

You can create a table in HBase using the createTable() method of HBaseAdmin class. This class belongs to the org.apache.hadoop.hbase.client package. Given below are the steps to create a table in HBase using java API.

Step1: Instantiate HBaseAdmin

This class requires the Configuration object as a parameter, therefore initially instantiate the Configuration class and pass this instance to HBaseAdmin.

Configuration conf = HBaseConfiguration.create();
HBaseAdmin admin = new HBaseAdmin(conf);

Step2: Create TableDescriptor

HTableDescriptor is a class that belongs to the org.apache.hadoop.hbase class. This class is like a container of table names and column families.

//creating table descriptor
HTableDescriptor table = new HTableDescriptor(toBytes("Table name"));

//creating column family descriptor
HColumnDescriptor family = new HColumnDescriptor(toBytes("column family"));

//adding coloumn family to HTable
table.addFamily(family);

Step 3: Execute through Admin

Using the createTable() method of HBaseAdmin class, you can execute the created table in Admin mode.

admin.createTable(table);

Given below is the complete program to create a table via admin.

import java.io.IOException;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.HColumnDescriptor;
import org.apache.hadoop.hbase.HTableDescriptor;
import org.apache.hadoop.hbase.client.HBaseAdmin;
import org.apache.hadoop.hbase.TableName;

import org.apache.hadoop.conf.Configuration;

public class CreateTable {
      
   public static void main(String[] args) throws IOException {

      // Instantiating configuration class
      Configuration con = HBaseConfiguration.create();

      // Instantiating HbaseAdmin class
      HBaseAdmin admin = new HBaseAdmin(con);

      // Instantiating table descriptor class
      HTableDescriptor tableDescriptor = new
      HTableDescriptor(TableName.valueOf("emp"));

      // Adding column families to table descriptor
      tableDescriptor.addFamily(new HColumnDescriptor("personal"));
      tableDescriptor.addFamily(new HColumnDescriptor("professional"));

      // Execute the table through admin
      admin.createTable(tableDescriptor);
      System.out.println(" Table created ");
   }
}

Compile and execute the above program as shown below.

$javac CreateTable.java
$java CreateTable

The following should be the output:

Table created

HBase - Listing Table

Listing a Table using HBase Shell

list is the command that is used to list all the tables in HBase. Given below is the syntax of the list command.

hbase(main):001:0 > list

When you type this command and execute in HBase prompt, it will display the list of all the tables in HBase as shown below.

hbase(main):001:0> list
TABLE
emp

Here you can observe a table named emp.

Listing Tables Using Java API

Follow the steps given below to get the list of tables from HBase using java API.

Step 1

You have a method called listTables() in the class HBaseAdmin to get the list of all the tables in HBase. This method returns an array of HTableDescriptor objects.

//creating a configuration object
Configuration conf = HBaseConfiguration.create();

//Creating HBaseAdmin object
HBaseAdmin admin = new HBaseAdmin(conf);

//Getting all the list of tables using HBaseAdmin object
HTableDescriptor[] tableDescriptor = admin.listTables();

Step 2

You can get the length of the HTableDescriptor[] array using the length variable of the HTableDescriptor class. Get the name of the tables from this object using getNameAsString() method. Run the ‘for’ loop using these and get the list of the tables in HBase.

Given below is the program to list all the tables in HBase using Java API.

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.HTableDescriptor;
import org.apache.hadoop.hbase.MasterNotRunningException;
import org.apache.hadoop.hbase.client.HBaseAdmin;

public class ListTables {

   public static void main(String args[])throws MasterNotRunningException, IOException{

      // Instantiating a configuration class
      Configuration conf = HBaseConfiguration.create();

      // Instantiating HBaseAdmin class
      HBaseAdmin admin = new HBaseAdmin(conf);

      // Getting all the list of tables using HBaseAdmin object
      HTableDescriptor[] tableDescriptor = admin.listTables();

      // printing all the table names.
      for (int i=0; i<tableDescriptor.length;i++ ){
         System.out.println(tableDescriptor[i].getNameAsString());
      }
   
   }
}

Compile and execute the above program as shown below.

$javac ListTables.java
$java ListTables

The following should be the output:

User
emp

HBase - Disabling a Table

Disabling a Table using HBase Shell

To delete a table or change its settings, you need to first disable the table using the disable command. You can re-enable it using the enable command.

Given below is the syntax to disable a table:

disable ‘emp’

Example

Given below is an example that shows how to disable a table.

hbase(main):025:0> disable 'emp'
0 row(s) in 1.2760 seconds

Verification

After disabling the table, you can still sense its existence through list and exists commands. You cannot scan it. It will give you the following error.

hbase(main):028:0> scan 'emp'
ROW         COLUMN + CELL
ERROR: emp is disabled.

is_disabled

This command is used to find whether a table is disabled. Its syntax is as follows.

hbase> is_disabled 'table name'

The following example verifies whether the table named emp is disabled. If it is disabled, it will return true and if not, it will return false.

hbase(main):031:0> is_disabled 'emp'
true
0 row(s) in 0.0440 seconds

disable_all

This command is used to disable all the tables matching the given regex. The syntax for disable_all command is given below.

hbase> disable_all 'r.*'

Suppose there are 5 tables in HBase, namely raja, rajani, rajendra, rajesh, and raju. The following code will disable all the tables starting with raj.

hbase(main):002:07> disable_all 'raj.*'
raja
rajani
rajendra
rajesh
raju
Disable the above 5 tables (y/n)?
y
5 tables successfully disabled

Disable a Table Using Java API

To verify whether a table is disabled, isTableDisabled() method is used and to disable a table, disableTable() method is used. These methods belong to the HBaseAdmin class. Follow the steps given below to disable a table.

Step 1

Instantiate HBaseAdmin class as shown below.

// Creating configuration object
Configuration conf = HBaseConfiguration.create();

// Creating HBaseAdmin object
HBaseAdmin admin = new HBaseAdmin(conf);

Step 2

Verify whether the table is disabled using isTableDisabled() method as shown below.

Boolean b = admin.isTableDisabled("emp");

Step 3

If the table is not disabled, disable it as shown below.

if(!b){
   admin.disableTable("emp");
   System.out.println("Table disabled");
}

Given below is the complete program to verify whether the table is disabled; if not, how to disable it.

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.MasterNotRunningException;
import org.apache.hadoop.hbase.client.HBaseAdmin;

public class DisableTable{

   public static void main(String args[]) throws MasterNotRunningException, IOException{

      // Instantiating configuration class
      Configuration conf = HBaseConfiguration.create();
 
      // Instantiating HBaseAdmin class
      HBaseAdmin admin = new HBaseAdmin(conf);

      // Verifying weather the table is disabled
      Boolean bool = admin.isTableDisabled("emp");
      System.out.println(bool);

      // Disabling the table using HBaseAdmin object
      if(!bool){
         admin.disableTable("emp");
         System.out.println("Table disabled");
      }
   }
}

Compile and execute the above program as shown below.

$javac DisableTable.java
$java DsiableTable

The following should be the output:

false
Table disabled

HBase - Enabling a Table

Enabling a Table using HBase Shell

Syntax to enable a table:

enable ‘emp’

Example

Given below is an example to enable a table.

hbase(main):005:0> enable 'emp'
0 row(s) in 0.4580 seconds

Verification

After enabling the table, scan it. If you can see the schema, your table is successfully enabled.

hbase(main):006:0> scan 'emp'

   ROW                        COLUMN + CELL

1 column = personal data:city, timestamp = 1417516501, value = hyderabad

1 column = personal data:name, timestamp = 1417525058, value = ramu

1 column = professional data:designation, timestamp = 1417532601, value = manager

1 column = professional data:salary, timestamp = 1417524244109, value = 50000

2 column = personal data:city, timestamp = 1417524574905, value = chennai

2 column = personal data:name, timestamp = 1417524556125, value = ravi

2 column = professional data:designation, timestamp = 14175292204, value = sr:engg

2 column = professional data:salary, timestamp = 1417524604221, value = 30000 

3 column = personal data:city, timestamp = 1417524681780, value = delhi

3 column = personal data:name, timestamp = 1417524672067, value = rajesh

3 column = professional data:designation, timestamp = 14175246987, value = jr:engg

3 column = professional data:salary, timestamp = 1417524702514, value = 25000

3 row(s) in 0.0400 seconds

is_enabled

This command is used to find whether a table is enabled. Its syntax is as follows:

hbase> is_enabled 'table name'

The following code verifies whether the table named emp is enabled. If it is enabled, it will return true and if not, it will return false.

hbase(main):031:0> is_enabled 'emp'
true
0 row(s) in 0.0440 seconds

Enable a Table Using Java API

To verify whether a table is enabled, isTableEnabled() method is used; and to enable a table, enableTable() method is used. These methods belong to HBaseAdmin class. Follow the steps given below to enable a table.

Step1

Instantiate HBaseAdmin class as shown below.

// Creating configuration object
Configuration conf = HBaseConfiguration.create();

// Creating HBaseAdmin object
HBaseAdmin admin = new HBaseAdmin(conf);

Step 2

Verify whether the table is enabled using isTableEnabled() method as shown below.

Boolean bool = admin.isTableEnabled("emp");

Step 3

If the table is not disabled, disable it as shown below.

if(!bool){
   admin.enableTable("emp");
   System.out.println("Table enabled");
}

Given below is the complete program to verify whether the table is enabled and if it is not, then how to enable it.

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.MasterNotRunningException;
import org.apache.hadoop.hbase.client.HBaseAdmin;

public class EnableTable{

   public static void main(String args[]) throws MasterNotRunningException, IOException{

      // Instantiating configuration class
      Configuration conf = HBaseConfiguration.create();

      // Instantiating HBaseAdmin class
      HBaseAdmin admin = new HBaseAdmin(conf);

      // Verifying whether the table is disabled
      Boolean bool = admin.isTableEnabled("emp");
      System.out.println(bool);

      // Enabling the table using HBaseAdmin object
      if(!bool){
         admin.enableTable("emp");
         System.out.println("Table Enabled");
      }
   }
}

Compile and execute the above program as shown below.

$javac EnableTable.java
$java EnableTable

The following should be the output:

false
Table Enabled

HBase - Describe & Alter

describe

This command returns the description of the table. Its syntax is as follows:

hbase> describe 'table name'

Given below is the output of the describe command on the emp table.

hbase(main):006:0> describe 'emp'
   DESCRIPTION
      ENABLED
      
'emp', {NAME ⇒ 'READONLY', DATA_BLOCK_ENCODING ⇒ 'NONE', BLOOMFILTER
⇒ 'ROW', REPLICATION_SCOPE ⇒ '0', COMPRESSION ⇒ 'NONE', VERSIONS ⇒
'1', TTL true

⇒ 'FOREVER', MIN_VERSIONS ⇒ '0', KEEP_DELETED_CELLS ⇒ 'false',
BLOCKSIZE ⇒ '65536', IN_MEMORY ⇒ 'false', BLOCKCACHE ⇒ 'true'}, {NAME
⇒ 'personal

data', DATA_BLOCK_ENCODING ⇒ 'NONE', BLOOMFILTER ⇒ 'ROW',
REPLICATION_SCOPE ⇒ '0', VERSIONS ⇒ '5', COMPRESSION ⇒ 'NONE',
MIN_VERSIONS ⇒ '0', TTL

⇒ 'FOREVER', KEEP_DELETED_CELLS ⇒ 'false', BLOCKSIZE ⇒ '65536',
IN_MEMORY ⇒ 'false', BLOCKCACHE ⇒ 'true'}, {NAME ⇒ 'professional
data', DATA_BLO

CK_ENCODING ⇒ 'NONE', BLOOMFILTER ⇒ 'ROW', REPLICATION_SCOPE ⇒ '0',
VERSIONS ⇒ '1', COMPRESSION ⇒ 'NONE', MIN_VERSIONS ⇒ '0', TTL ⇒
'FOREVER', K

EEP_DELETED_CELLS ⇒ 'false', BLOCKSIZE ⇒ '65536', IN_MEMORY ⇒
'false', BLOCKCACHE ⇒ 'true'}, {NAME ⇒ 'table_att_unset',
DATA_BLOCK_ENCODING ⇒ 'NO 

NE', BLOOMFILTER ⇒ 'ROW', REPLICATION_SCOPE ⇒ '0', COMPRESSION ⇒
'NONE', VERSIONS ⇒ '1', TTL ⇒ 'FOREVER', MIN_VERSIONS ⇒ '0',
KEEP_DELETED_CELLS

⇒ 'false', BLOCKSIZE ⇒ '6

alter

Alter is the command used to make changes to an existing table. Using this command, you can change the maximum number of cells of a column family, set and delete table scope operators, and delete a column family from a table.

Changing the Maximum Number of Cells of a Column Family

Given below is the syntax to change the maximum number of cells of a column family.

hbase> alter 't1', NAME ⇒ 'f1', VERSIONS ⇒ 5

In the following example, the maximum number of cells is set to 5.

hbase(main):003:0> alter 'emp', NAME ⇒ 'personal data', VERSIONS ⇒ 5
Updating all regions with the new schema...
0/1 regions updated.
1/1 regions updated.
Done.
0 row(s) in 2.3050 seconds

Table Scope Operators

Using alter, you can set and remove table scope operators such as MAX_FILESIZE, READONLY, MEMSTORE_FLUSHSIZE, DEFERRED_LOG_FLUSH, etc.

Setting Read Only

Below given is the syntax to make a table read only.

hbase>alter 't1', READONLY(option)

In the following example, we have made the emp table read only.

hbase(main):006:0> alter 'emp', READONLY
Updating all regions with the new schema...
0/1 regions updated.
1/1 regions updated.
Done.
0 row(s) in 2.2140 seconds

Removing Table Scope Operators

We can also remove the table scope operators. Given below is the syntax to remove ‘MAX_FILESIZE’ from emp table.

hbase> alter 't1', METHOD ⇒ 'table_att_unset', NAME ⇒ 'MAX_FILESIZE'

Deleting a Column Family

Using alter, you can also delete a column family. Given below is the syntax to delete a column family using alter.

hbase> alter ‘ table name ’, ‘delete’ ⇒ ‘ column family ’ 

Given below is an example to delete a column family from the ‘emp’ table.

Assume there is a table named employee in HBase. It contains the following data:

hbase(main):006:0> scan 'employee'

   ROW                   COLUMN+CELL

row1 column = personal:city, timestamp = 1418193767, value = hyderabad

row1 column = personal:name, timestamp = 1418193806767, value = raju

row1 column = professional:designation, timestamp = 1418193767, value = manager

row1 column = professional:salary, timestamp = 1418193806767, value = 50000

1 row(s) in 0.0160 seconds 

Now let us delete the column family named professional using the alter command.

hbase(main):007:0> alter 'employee','delete'⇒'professional'
Updating all regions with the new schema...
0/1 regions updated.
1/1 regions updated.
Done.
0 row(s) in 2.2380 seconds 

Now verify the data in the table after alteration. Observe the column family ‘professional’ is no more, since we have deleted it.

hbase(main):003:0> scan 'employee'
   ROW             COLUMN + CELL
row1 column = personal:city, timestamp = 14181936767, value = hyderabad

row1 column = personal:name, timestamp = 1418193806767, value = raju

1 row(s) in 0.0830 seconds

Adding a Column Family Using Java API

You can add a column family to a table using the method addColumn() of HBAseAdmin class. Follow the steps given below to add a column family to a table.

Step 1

Instantiate the HBaseAdmin class.

// Instantiating configuration object
Configuration conf = HBaseConfiguration.create();

// Instantiating HBaseAdmin class
HBaseAdmin admin = new HBaseAdmin(conf); 

Step 2

The addColumn() method requires a table name and an object of HColumnDescriptor class. Therefore instantiate the HColumnDescriptor class. The constructor of HColumnDescriptor in turn requires a column family name that is to be added. Here we are adding a column family named “contactDetails” to the existing “employee” table.

// Instantiating columnDescriptor object

HColumnDescriptor columnDescriptor = new
HColumnDescriptor("contactDetails");

Step 3

Add the column family using addColumn method. Pass the table name and the HColumnDescriptor class object as parameters to this method.

// Adding column family
admin.addColumn("employee", new HColumnDescriptor("columnDescriptor"));

Given below is the complete program to add a column family to an existing table.

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.HColumnDescriptor;
import org.apache.hadoop.hbase.MasterNotRunningException;
import org.apache.hadoop.hbase.client.HBaseAdmin;

public class AddColoumn{

   public static void main(String args[]) throws MasterNotRunningException, IOException{

      // Instantiating configuration class.
      Configuration conf = HBaseConfiguration.create();

      // Instantiating HBaseAdmin class.
      HBaseAdmin admin = new HBaseAdmin(conf);

      // Instantiating columnDescriptor class
      HColumnDescriptor columnDescriptor = new HColumnDescriptor("contactDetails");
      
      // Adding column family
      admin.addColumn("employee", columnDescriptor);
      System.out.println("coloumn added");
   }
}

Compile and execute the above program as shown below.

$javac AddColumn.java
$java AddColumn

The above compilation works only if you have set the classpath in “ .bashrc ”. If you haven't, follow the procedure given below to compile your .java file.

//if "/home/home/hadoop/hbase " is your Hbase home folder then.

$javac -cp /home/hadoop/hbase/lib/*: Demo.java

If everything goes well, it will produce the following output:

column added

Deleting a Column Family Using Java API

You can delete a column family from a table using the method deleteColumn() of HBAseAdmin class. Follow the steps given below to add a column family to a table.

Step1

Instantiate the HBaseAdmin class.

// Instantiating configuration object
Configuration conf = HBaseConfiguration.create();

// Instantiating HBaseAdmin class
HBaseAdmin admin = new HBaseAdmin(conf); 

Step2

Add the column family using deleteColumn() method. Pass the table name and the column family name as parameters to this method.

// Deleting column family
admin.deleteColumn("employee", "contactDetails"); 

Given below is the complete program to delete a column family from an existing table.

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.MasterNotRunningException;
import org.apache.hadoop.hbase.client.HBaseAdmin;

public class DeleteColoumn{

   public static void main(String args[]) throws MasterNotRunningException, IOException{

      // Instantiating configuration class.
      Configuration conf = HBaseConfiguration.create();

      // Instantiating HBaseAdmin class.
      HBaseAdmin admin = new HBaseAdmin(conf);

      // Deleting a column family
      admin.deleteColumn("employee","contactDetails");
      System.out.println("coloumn deleted"); 
   }
}

Compile and execute the above program as shown below.

$javac DeleteColumn.java
$java DeleteColumn

The following should be the output:

column deleted

HBase - Exists

Existence of Table using HBase Shell

You can verify the existence of a table using the exists command. The following example shows how to use this command.

hbase(main):024:0> exists 'emp'
Table emp does exist

0 row(s) in 0.0750 seconds

==================================================================

hbase(main):015:0> exists 'student'
Table student does not exist

0 row(s) in 0.0480 seconds

Verifying the Existence of Table Using Java API

You can verify the existence of a table in HBase using the tableExists() method of the HBaseAdmin class. Follow the steps given below to verify the existence of a table in HBase.

Step 1

Instantiate the HBaseAdimn class

// Instantiating configuration object
Configuration conf = HBaseConfiguration.create();

// Instantiating HBaseAdmin class
HBaseAdmin admin = new HBaseAdmin(conf); 

Step 2

Verify the existence of the table using the tableExists( ) method.

Given below is the java program to test the existence of a table in HBase using java API.

import java.io.IOException;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.client.HBaseAdmin;

public class TableExists{

   public static void main(String args[])throws IOException{

      // Instantiating configuration class
      Configuration conf = HBaseConfiguration.create();

      // Instantiating HBaseAdmin class
      HBaseAdmin admin = new HBaseAdmin(conf);

      // Verifying the existance of the table
      boolean bool = admin.tableExists("emp");
      System.out.println( bool);
   }
} 

Compile and execute the above program as shown below.

$javac TableExists.java
$java TableExists 

The following should be the output:

true

HBase - Drop a Table

Dropping a Table using HBase Shell

Using the drop command, you can delete a table. Before dropping a table, you have to disable it.

hbase(main):018:0> disable 'emp'
0 row(s) in 1.4580 seconds

hbase(main):019:0> drop 'emp'
0 row(s) in 0.3060 seconds

Verify whether the table is deleted using the exists command.

hbase(main):020:07gt; exists 'emp'
Table emp does not exist
0 row(s) in 0.0730 seconds

drop_all

This command is used to drop the tables matching the “regex” given in the command. Its syntax is as follows:

hbase> drop_all ‘t.*’ 

Note: Before dropping a table, you must disable it.

Example

Assume there are tables named raja, rajani, rajendra, rajesh, and raju.

hbase(main):017:0> list
TABLE
raja
rajani
rajendra 
rajesh
raju
9 row(s) in 0.0270 seconds

All these tables start with the letters raj. First of all, let us disable all these tables using the disable_all command as shown below.

hbase(main):002:0> disable_all 'raj.*'
raja
rajani
rajendra
rajesh
raju
Disable the above 5 tables (y/n)?
y
5 tables successfully disabled

Now you can delete all of them using the drop_all command as given below.

hbase(main):018:0> drop_all 'raj.*'
raja
rajani
rajendra
rajesh
raju
Drop the above 5 tables (y/n)?
y
5 tables successfully dropped

Deleting a Table Using Java API

You can delete a table using the deleteTable() method in the HBaseAdmin class. Follow the steps given below to delete a table using java API.

Step 1

Instantiate the HBaseAdmin class.

// creating a configuration object
Configuration conf = HBaseConfiguration.create();

// Creating HBaseAdmin object
HBaseAdmin admin = new HBaseAdmin(conf); 

Step 2

Disable the table using the disableTable() method of the HBaseAdmin class.

admin.disableTable("emp1");

Step 3

Now delete the table using the deleteTable() method of the HBaseAdmin class.

admin.deleteTable("emp12");

Given below is the complete java program to delete a table in HBase.

import java.io.IOException;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.client.HBaseAdmin;

public class DeleteTable {

   public static void main(String[] args) throws IOException {

      // Instantiating configuration class
      Configuration conf = HBaseConfiguration.create();

      // Instantiating HBaseAdmin class
      HBaseAdmin admin = new HBaseAdmin(conf);

      // disabling table named emp
      admin.disableTable("emp12");

      // Deleting emp
      admin.deleteTable("emp12");
      System.out.println("Table deleted");
   }
}

Compile and execute the above program as shown below.

$javac DeleteTable.java
$java DeleteTable

The following should be the output:

Table deleted

HBase - Shutting Down

exit

You exit the shell by typing the exit command.

hbase(main):021:0> exit

Stopping HBase

To stop HBase, browse to the HBase home folder and type the following command.

./bin/stop-hbase.sh

Stopping HBase Using Java API

You can shut down the HBase using the shutdown() method of the HBaseAdmin class. Follow the steps given below to shut down HBase:

Step 1

Instantiate the HbaseAdmin class.

// Instantiating configuration object
Configuration conf = HBaseConfiguration.create();

// Instantiating HBaseAdmin object
HBaseAdmin admin = new HBaseAdmin(conf);

Step 2

Shut down the HBase using the shutdown() method of the HBaseAdmin class.

admin.shutdown();

Given below is the program to stop the HBase.

import java.io.IOException;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.client.HBaseAdmin;

public class ShutDownHbase{

   public static void main(String args[])throws IOException {

      // Instantiating configuration class
      Configuration conf = HBaseConfiguration.create();

      // Instantiating HBaseAdmin class
      HBaseAdmin admin = new HBaseAdmin(conf);

      // Shutting down HBase
      System.out.println("Shutting down hbase");
      admin.shutdown();
   }
}

Compile and execute the above program as shown below.

$javac ShutDownHbase.java
$java ShutDownHbase

The following should be the output:

Shutting down hbase

HBase - Client API

This chapter describes the java client API for HBase that is used to perform CRUD operations on HBase tables. HBase is written in Java and has a Java Native API. Therefore it provides programmatic access to Data Manipulation Language (DML).

Class HBase Configuration

Adds HBase configuration files to a Configuration. This class belongs to the org.apache.hadoop.hbase package.

Methods and description

S.No.	Methods and Description
1	static org.apache.hadoop.conf.Configuration create() This method creates a Configuration with HBase resources.

Class HTable

HTable is an HBase internal class that represents an HBase table. It is an implementation of table that is used to communicate with a single HBase table. This class belongs to the org.apache.hadoop.hbase.client class.

Constructors

S.No.	Constructors and Description
1	HTable()
2	HTable(TableName tableName, ClusterConnection connection, ExecutorService pool) Using this constructor, you can create an object to access an HBase table.

Methods and description

S.No.	Methods and Description
1	void close() Releases all the resources of the HTable.
2	void delete(Delete delete) Deletes the specified cells/row.
3	boolean exists(Get get) Using this method, you can test the existence of columns in the table, as specified by Get.
4	Result get(Get get) Retrieves certain cells from a given row.
5	org.apache.hadoop.conf.Configuration getConfiguration() Returns the Configuration object used by this instance.
6	TableName getName() Returns the table name instance of this table.
7	HTableDescriptor getTableDescriptor() Returns the table descriptor for this table.
8	byte[] getTableName() Returns the name of this table.
9	void put(Put put) Using this method, you can insert data into the table.

Class Put

This class is used to perform Put operations for a single row. It belongs to the org.apache.hadoop.hbase.client package.

Constructors

S.No.	Constructors and Description
1	Put(byte[] row) Using this constructor, you can create a Put operation for the specified row.
2	Put(byte[] rowArray, int rowOffset, int rowLength) Using this constructor, you can make a copy of the passed-in row key to keep local.
3	Put(byte[] rowArray, int rowOffset, int rowLength, long ts) Using this constructor, you can make a copy of the passed-in row key to keep local.
4	Put(byte[] row, long ts) Using this constructor, we can create a Put operation for the specified row, using a given timestamp.

Methods

S.No.	Methods and Description
1	Put add(byte[] family, byte[] qualifier, byte[] value) Adds the specified column and value to this Put operation.
2	Put add(byte[] family, byte[] qualifier, long ts, byte[] value) Adds the specified column and value, with the specified timestamp as its version to this Put operation.
3	Put add(byte[] family, ByteBuffer qualifier, long ts, ByteBuffer value) Adds the specified column and value, with the specified timestamp as its version to this Put operation.
4	Put add(byte[] family, ByteBuffer qualifier, long ts, ByteBuffer value) Adds the specified column and value, with the specified timestamp as its version to this Put operation.

Class Get

This class is used to perform Get operations on a single row. This class belongs to the org.apache.hadoop.hbase.client package.

Constructor

S.No.	Constructor and Description
1	Get(byte[] row) Using this constructor, you can create a Get operation for the specified row.
2	Get(Get get)

Methods

S.No.	Methods and Description
1	Get addColumn(byte[] family, byte[] qualifier) Retrieves the column from the specific family with the specified qualifier.
2	Get addFamily(byte[] family) Retrieves all columns from the specified family.

Class Delete

This class is used to perform Delete operations on a single row. To delete an entire row, instantiate a Delete object with the row to delete. This class belongs to the org.apache.hadoop.hbase.client package.

Constructor

S.No.	Constructor and Description
1	Delete(byte[] row) Creates a Delete operation for the specified row.
2	Delete(byte[] rowArray, int rowOffset, int rowLength) Creates a Delete operation for the specified row and timestamp.
3	Delete(byte[] rowArray, int rowOffset, int rowLength, long ts) Creates a Delete operation for the specified row and timestamp.
4	Delete(byte[] row, long timestamp) Creates a Delete operation for the specified row and timestamp.

Methods

S.No.	Methods and Description
1	Delete addColumn(byte[] family, byte[] qualifier) Deletes the latest version of the specified column.
2	Delete addColumns(byte[] family, byte[] qualifier, long timestamp) Deletes all versions of the specified column with a timestamp less than or equal to the specified timestamp.
3	Delete addFamily(byte[] family) Deletes all versions of all columns of the specified family.
4	Delete addFamily(byte[] family, long timestamp) Deletes all columns of the specified family with a timestamp less than or equal to the specified timestamp.

Class Result

This class is used to get a single row result of a Get or a Scan query.

Constructors

S.No.	Constructors
1	Result() Using this constructor, you can create an empty Result with no KeyValue payload; returns null if you call raw Cells().

Methods

S.No.	Methods and Description
1	byte[] getValue(byte[] family, byte[] qualifier) This method is used to get the latest version of the specified column.
2	byte[] getRow() This method is used to retrieve the row key that corresponds to the row from which this Result was created.

HBase - Create Data

Inserting Data using HBase Shell

This chapter demonstrates how to create data in an HBase table. To create data in an HBase table, the following commands and methods are used:

• put command,

• add() method of Put class, and

• put() method of HTable class.

As an example, we are going to create the following table in HBase.

Using put command, you can insert rows into a table. Its syntax is as follows:

put ’<table name>’,’row1’,’<colfamily:colname>’,’<value>’

Inserting the First Row

Let us insert the first row values into the emp table as shown below.

hbase(main):005:0> put 'emp','1','personal data:name','raju'
0 row(s) in 0.6600 seconds
hbase(main):006:0> put 'emp','1','personal data:city','hyderabad'
0 row(s) in 0.0410 seconds
hbase(main):007:0> put 'emp','1','professional
data:designation','manager'
0 row(s) in 0.0240 seconds
hbase(main):007:0> put 'emp','1','professional data:salary','50000'
0 row(s) in 0.0240 seconds

Insert the remaining rows using the put command in the same way. If you insert the whole table, you will get the following output.

hbase(main):022:0> scan 'emp'

   ROW                        COLUMN+CELL
1 column=personal data:city, timestamp=1417524216501, value=hyderabad

1 column=personal data:name, timestamp=1417524185058, value=ramu

1 column=professional data:designation, timestamp=1417524232601,

 value=manager
 
1 column=professional data:salary, timestamp=1417524244109, value=50000

2 column=personal data:city, timestamp=1417524574905, value=chennai

2 column=personal data:name, timestamp=1417524556125, value=ravi

2 column=professional data:designation, timestamp=1417524592204,

 value=sr:engg
 
2 column=professional data:salary, timestamp=1417524604221, value=30000

3 column=personal data:city, timestamp=1417524681780, value=delhi

3 column=personal data:name, timestamp=1417524672067, value=rajesh

3 column=professional data:designation, timestamp=1417524693187,

value=jr:engg
3 column=professional data:salary, timestamp=1417524702514,

value=25000 

Inserting Data Using Java API

You can insert data into Hbase using the add() method of the Put class. You can save it using the put() method of the HTable class. These classes belong to the org.apache.hadoop.hbase.client package. Below given are the steps to create data in a Table of HBase.

Step 1:Instantiate the Configuration Class

The Configuration class adds HBase configuration files to its object. You can create a configuration object using the create() method of the HbaseConfiguration class as shown below.

Configuration conf = HbaseConfiguration.create();

Step 2:Instantiate the HTable Class

You have a class called HTable, an implementation of Table in HBase. This class is used to communicate with a single HBase table. While instantiating this class, it accepts configuration object and table name as parameters. You can instantiate HTable class as shown below.

HTable hTable = new HTable(conf, tableName);

Step 3: Instantiate the PutClass

To insert data into an HBase table, the add() method and its variants are used. This method belongs to Put, therefore instantiate the put class. This class requires the row name you want to insert the data into, in string format. You can instantiate the Put class as shown below.

Put p = new Put(Bytes.toBytes("row1"));

Step 4: InsertData

The add() method of Put class is used to insert data. It requires 3 byte arrays representing column family, column qualifier (column name), and the value to be inserted, respectively. Insert data into the HBase table using the add() method as shown below.

p.add(Bytes.toBytes("coloumn family "), Bytes.toBytes("column
name"),Bytes.toBytes("value"));

Step 5: Save the Data in Table

After inserting the required rows, save the changes by adding the put instance to the put() method of HTable class as shown below.

hTable.put(p); 

Step 6: Close the HTable Instance

After creating data in the HBase Table, close the HTable instance using the close() method as shown below.

hTable.close(); 

Given below is the complete program to create data in HBase Table.

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.client.HTable;
import org.apache.hadoop.hbase.client.Put;
import org.apache.hadoop.hbase.util.Bytes;

public class InsertData{

   public static void main(String[] args) throws IOException {

      // Instantiating Configuration class
      Configuration config = HBaseConfiguration.create();

      // Instantiating HTable class
      HTable hTable = new HTable(config, "emp");

      // Instantiating Put class
      // accepts a row name.
      Put p = new Put(Bytes.toBytes("row1")); 

      // adding values using add() method
      // accepts column family name, qualifier/row name ,value
      p.add(Bytes.toBytes("personal"),
      Bytes.toBytes("name"),Bytes.toBytes("raju"));

      p.add(Bytes.toBytes("personal"),
      Bytes.toBytes("city"),Bytes.toBytes("hyderabad"));

      p.add(Bytes.toBytes("professional"),Bytes.toBytes("designation"),
      Bytes.toBytes("manager"));

      p.add(Bytes.toBytes("professional"),Bytes.toBytes("salary"),
      Bytes.toBytes("50000"));
      
      // Saving the put Instance to the HTable.
      hTable.put(p);
      System.out.println("data inserted");
      
      // closing HTable
      hTable.close();
   }
}

Compile and execute the above program as shown below.

$javac InsertData.java
$java InsertData

The following should be the output:

data inserted

HBase - Update Data

Updating Data using HBase Shell

You can update an existing cell value using the put command. To do so, just follow the same syntax and mention your new value as shown below.

put ‘table name’,’row ’,'Column family:column name',’new value’

The newly given value replaces the existing value, updating the row.

Example

Suppose there is a table in HBase called emp with the following data.

hbase(main):003:0> scan 'emp'
 ROW              COLUMN + CELL
row1 column = personal:name, timestamp = 1418051555, value = raju
row1 column = personal:city, timestamp = 1418275907, value = Hyderabad
row1 column = professional:designation, timestamp = 14180555,value = manager
row1 column = professional:salary, timestamp = 1418035791555,value = 50000
1 row(s) in 0.0100 seconds

The following command will update the city value of the employee named ‘Raju’ to Delhi.

hbase(main):002:0> put 'emp','row1','personal:city','Delhi'
0 row(s) in 0.0400 seconds

The updated table looks as follows where you can observe the city of Raju has been changed to ‘Delhi’.

hbase(main):003:0> scan 'emp'
  ROW          COLUMN + CELL
row1 column = personal:name, timestamp = 1418035791555, value = raju
row1 column = personal:city, timestamp = 1418274645907, value = Delhi
row1 column = professional:designation, timestamp = 141857555,value = manager
row1 column = professional:salary, timestamp = 1418039555, value = 50000
1 row(s) in 0.0100 seconds

Updating Data Using Java API

You can update the data in a particular cell using the put() method. Follow the steps given below to update an existing cell value of a table.

Step 1: Instantiate the Configuration Class

Configuration class adds HBase configuration files to its object. You can create a configuration object using the create() method of the HbaseConfiguration class as shown below.

Configuration conf = HbaseConfiguration.create();

Step 2: Instantiate the HTable Class

You have a class called HTable, an implementation of Table in HBase. This class is used to communicate with a single HBase table. While instantiating this class, it accepts the configuration object and the table name as parameters. You can instantiate the HTable class as shown below.

HTable hTable = new HTable(conf, tableName);

Step 3: Instantiate the Put Class

To insert data into HBase Table, the add() method and its variants are used. This method belongs to Put, therefore instantiate the put class. This class requires the row name you want to insert the data into, in string format. You can instantiate the Put class as shown below.

Put p = new Put(Bytes.toBytes("row1"));

Step 4: Update an Existing Cell

The add() method of Put class is used to insert data. It requires 3 byte arrays representing column family, column qualifier (column name), and the value to be inserted, respectively. Insert data into HBase table using the add() method as shown below.

p.add(Bytes.toBytes("coloumn family "), Bytes.toBytes("column
name"),Bytes.toBytes("value"));
p.add(Bytes.toBytes("personal"),
Bytes.toBytes("city"),Bytes.toBytes("Delih"));

Step 5: Save the Data in Table

After inserting the required rows, save the changes by adding the put instance to the put() method of the HTable class as shown below.

hTable.put(p); 

Step 6: Close HTable Instance

After creating data in HBase Table, close the HTable instance using the close() method as shown below.

hTable.close();

Given below is the complete program to update data in a particular table.

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.client.HTable;
import org.apache.hadoop.hbase.client.Put;
import org.apache.hadoop.hbase.util.Bytes;

public class UpdateData{

   public static void main(String[] args) throws IOException {

      // Instantiating Configuration class
      Configuration config = HBaseConfiguration.create();

      // Instantiating HTable class
      HTable hTable = new HTable(config, "emp");

      // Instantiating Put class
      //accepts a row name
      Put p = new Put(Bytes.toBytes("row1"));

      // Updating a cell value
      p.add(Bytes.toBytes("personal"),
      Bytes.toBytes("city"),Bytes.toBytes("Delih"));

      // Saving the put Instance to the HTable.
      hTable.put(p);
      System.out.println("data Updated");

      // closing HTable
      hTable.close();
   }
}

Compile and execute the above program as shown below.

$javac UpdateData.java
$java UpdateData

The following should be the output:

data Updated

HBase - Read Data

Reading Data using HBase Shell

The get command and the get() method of HTable class are used to read data from a table in HBase. Using get command, you can get a single row of data at a time. Its syntax is as follows:

get ’<table name>’,’row1’

Example

The following example shows how to use the get command. Let us scan the first row of the emp table.

hbase(main):012:0> get 'emp', '1'

   COLUMN                     CELL
   
personal : city timestamp = 1417521848375, value = hyderabad

personal : name timestamp = 1417521785385, value = ramu

professional: designation timestamp = 1417521885277, value = manager

professional: salary timestamp = 1417521903862, value = 50000

4 row(s) in 0.0270 seconds

Reading a Specific Column

Given below is the syntax to read a specific column using the get method.

hbase> get 'table name', ‘rowid’, {COLUMN ⇒ ‘column family:column name ’}

Example

Given below is the example to read a specific column in HBase table.

hbase(main):015:0> get 'emp', 'row1', {COLUMN ⇒ 'personal:name'}
  COLUMN                CELL  
personal:name timestamp = 1418035791555, value = raju
1 row(s) in 0.0080 seconds

Reading Data Using Java API

To read data from an HBase table, use the get() method of the HTable class. This method requires an instance of the Get class. Follow the steps given below to retrieve data from the HBase table.

Step 1: Instantiate the Configuration Class

Configuration class adds HBase configuration files to its object. You can create a configuration object using the create() method of the HbaseConfiguration class as shown below.

Configuration conf = HbaseConfiguration.create();

Step 2: Instantiate the HTable Class

You have a class called HTable, an implementation of Table in HBase. This class is used to communicate with a single HBase table. While instantiating this class, it accepts the configuration object and the table name as parameters. You can instantiate the HTable class as shown below.

HTable hTable = new HTable(conf, tableName);

Step 3: Instantiate the Get Class

You can retrieve data from the HBase table using the get() method of the HTable class. This method extracts a cell from a given row. It requires a Get class object as parameter. Create it as shown below.

Get get = new Get(toBytes("row1"));

Step 4: Read the Data

While retrieving data, you can get a single row by id, or get a set of rows by a set of row ids, or scan an entire table or a subset of rows.

You can retrieve an HBase table data using the add method variants in Get class.

To get a specific column from a specific column family, use the following method.

get.addFamily(personal) 

To get all the columns from a specific column family, use the following method.

get.addColumn(personal, name) 

Step 5: Get the Result

Get the result by passing your Get class instance to the get method of the HTable class. This method returns the Result class object, which holds the requested result. Given below is the usage of get() method.

Result result = table.get(g);  

Step 6: Reading Values from the Result Instance

The Result class provides the getValue() method to read the values from its instance. Use it as shown below to read the values from the Result instance.

byte [] value = result.getValue(Bytes.toBytes("personal"),Bytes.toBytes("name"));
byte [] value1 = result.getValue(Bytes.toBytes("personal"),Bytes.toBytes("city"));

Given below is the complete program to read values from an HBase table.

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.client.Get;
import org.apache.hadoop.hbase.client.HTable;
import org.apache.hadoop.hbase.client.Result;
import org.apache.hadoop.hbase.util.Bytes;

public class RetriveData{

   public static void main(String[] args) throws IOException, Exception{
   
      // Instantiating Configuration class
      Configuration config = HBaseConfiguration.create();

      // Instantiating HTable class
      HTable table = new HTable(config, "emp");

      // Instantiating Get class
      Get g = new Get(Bytes.toBytes("row1"));

      // Reading the data
      Result result = table.get(g);

      // Reading values from Result class object
      byte [] value = result.getValue(Bytes.toBytes("personal"),Bytes.toBytes("name"));

      byte [] value1 = result.getValue(Bytes.toBytes("personal"),Bytes.toBytes("city"));

      // Printing the values
      String name = Bytes.toString(value);
      String city = Bytes.toString(value1);
      
      System.out.println("name: " + name + " city: " + city);
   }
}

Compile and execute the above program as shown below.

$javac RetriveData.java
$java RetriveData

The following should be the output:

name: Raju city: Delhi

HBase - Delete Data

Deleting a Specific Cell in a Table

Using the delete command, you can delete a specific cell in a table. The syntax of delete command is as follows:

delete ‘<table name>’, ‘<row>’, ‘<column name >’, ‘<time stamp>’

Example

Here is an example to delete a specific cell. Here we are deleting the salary.

hbase(main):006:0> delete 'emp', '1', 'personal data:city',
1417521848375
0 row(s) in 0.0060 seconds

Deleting All Cells in a Table

Using the “deleteall” command, you can delete all the cells in a row. Given below is the syntax of deleteall command.

deleteall ‘<table name>’, ‘<row>’,

Example

Here is an example of “deleteall” command, where we are deleting all the cells of row1 of emp table.

hbase(main):007:0> deleteall 'emp','1'
0 row(s) in 0.0240 seconds

Verify the table using the scan command. A snapshot of the table after deleting the table is given below.

hbase(main):022:0> scan 'emp'

ROW                  COLUMN + CELL

2 column = personal data:city, timestamp = 1417524574905, value = chennai 

2 column = personal data:name, timestamp = 1417524556125, value = ravi

2 column = professional data:designation, timestamp = 1417524204, value = sr:engg

2 column = professional data:salary, timestamp = 1417524604221, value = 30000

3 column = personal data:city, timestamp = 1417524681780, value = delhi

3 column = personal data:name, timestamp = 1417524672067, value = rajesh
 
3 column = professional data:designation, timestamp = 1417523187, value = jr:engg

3 column = professional data:salary, timestamp = 1417524702514, value = 25000

Deleting Data Using Java API

You can delete data from an HBase table using the delete() method of the HTable class. Follow the steps given below to delete data from a table.

Step 1: Instantiate the Configuration Class

Configuration class adds HBase configuration files to its object. You can create a configuration object using the create() method of the the HbaseConfiguration class as shown below.

Configuration conf = HbaseConfiguration.create();

Step 2: Instantiate the HTable Class

You have a class called HTable, an implementation of Table in HBase. This class is used to communicate with a single HBase table. While instantiating this class, it accepts the configuration object and the table name as parameters. You can instantiate the HTable class as shown below.

HTable hTable = new HTable(conf, tableName); 

Step 3: Instantiate the Delete Class

Instantiate the Delete class by passing the rowid of the row that is to be deleted, in byte array format. You can also pass timestamp and Rowlock to this constructor.

Delete delete = new Delete(toBytes("row1"));

Step 4: Select the Data to be Deleted

You can delete the data using the delete methods of the Delete class. This class has various delete methods. Choose the columns or column families to be deleted using those methods. Take a look at the following examples that show the usage of Delete class methods.

delete.deleteColumn(Bytes.toBytes("personal"), Bytes.toBytes("name"));
delete.deleteFamily(Bytes.toBytes("professional"));

Step 5: Delete the Data

Delete the selected data by passing the delete instance to the delete() method of the HTable class as shown below.

table.delete(delete); 

Step 6: Close the HTableInstance

After deleting the data, close the HTable Instance.

table.close();

Given below is the complete program to delete data from the HBase table.

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.client.Delete;
import org.apache.hadoop.hbase.client.HTable;
import org.apache.hadoop.hbase.util.Bytes;

public class DeleteData {

   public static void main(String[] args) throws IOException {

      // Instantiating Configuration class
      Configuration conf = HBaseConfiguration.create();

      // Instantiating HTable class
      HTable table = new HTable(conf, "employee");

      // Instantiating Delete class
      Delete delete = new Delete(Bytes.toBytes("row1"));
      delete.deleteColumn(Bytes.toBytes("personal"), Bytes.toBytes("name"));
      delete.deleteFamily(Bytes.toBytes("professional"));

      // deleting the data
      table.delete(delete);

      // closing the HTable object
      table.close();
      System.out.println("data deleted.....");
   }
}

Compile and execute the above program as shown below.

$javac Deletedata.java
$java DeleteData

The following should be the output:

data deleted

HBase - Scan

Scaning using HBase Shell

The scan command is used to view the data in HTable. Using the scan command, you can get the table data. Its syntax is as follows:

scan ‘<table name>’ 

Example

The following example shows how to read data from a table using the scan command. Here we are reading the emp table.

hbase(main):010:0> scan 'emp'

ROW                           COLUMN + CELL

1 column = personal data:city, timestamp = 1417521848375, value = hyderabad
 
1 column = personal data:name, timestamp = 1417521785385, value = ramu

1 column = professional data:designation, timestamp = 1417585277,value = manager

1 column = professional data:salary, timestamp = 1417521903862, value = 50000

1 row(s) in 0.0370 seconds

Scanning Using Java API

The complete program to scan the entire table data using java API is as follows.

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.util.Bytes;

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;


public class ScanTable{

   public static void main(String args[]) throws IOException{

      // Instantiating Configuration class
      Configuration config = HBaseConfiguration.create();

      // Instantiating HTable class
      HTable table = new HTable(config, "emp");

      // Instantiating the Scan class
      Scan scan = new Scan();

      // Scanning the required columns
      scan.addColumn(Bytes.toBytes("personal"), Bytes.toBytes("name"));
      scan.addColumn(Bytes.toBytes("personal"), Bytes.toBytes("city"));

      // Getting the scan result
      ResultScanner scanner = table.getScanner(scan);

      // Reading values from scan result
      for (Result result = scanner.next(); result != null; result = Scanner.next())

      System.out.println("Found row : " + result);
      //closing the scanner
      scanner.close();
   }
}

Compile and execute the above program as shown below.

$javac ScanTable.java
$java ScanTable 

The following should be the output:

Found row :
keyvalues={row1/personal:city/1418275612888/Put/vlen=5/mvcc=0,
row1/personal:name/1418035791555/Put/vlen=4/mvcc=0}

HBase - Count & Truncate

count

You can count the number of rows of a table using the count command. Its syntax is as follows:

count ‘<table name>’ 

After deleting the first row, emp table will have two rows. Verify it as shown below.

hbase(main):023:0> count 'emp'
2 row(s) in 0.090 seconds
⇒ 2 

truncate

This command disables drops and recreates a table. The syntax of truncate is as follows:

hbase> truncate 'table name'

Example

Given below is the example of truncate command. Here we have truncated the emp table.

hbase(main):011:0> truncate 'emp'
Truncating 'one' table (it may take a while):
   - Disabling table...
   - Truncating table...
   0 row(s) in 1.5950 seconds

After truncating the table, use the scan command to verify. You will get a table with zero rows.

hbase(main):017:0> scan ‘emp’
ROW                  COLUMN + CELL
0 row(s) in 0.3110 seconds

HBase - Security

We can grant and revoke permissions to users in HBase. There are three commands for security purpose: grant, revoke, and user_permission.

grant

The grant command grants specific rights such as read, write, execute, and admin on a table to a certain user. The syntax of grant command is as follows:

hbase> grant <user> <permissions> [<table> [<column family> [&ltcolumn; qualifier>]]

We can grant zero or more privileges to a user from the set of RWXCA, where

• R - represents read privilege.
• W - represents write privilege.
• X - represents execute privilege.
• C - represents create privilege.
• A - represents admin privilege.

Given below is an example that grants all privileges to a user named ‘Howcodex’.

hbase(main):018:0> grant 'Howcodex', 'RWXCA'

revoke

The revoke command is used to revoke a user's access rights of a table. Its syntax is as follows:

hbase> revoke <user>

The following code revokes all the permissions from the user named ‘Howcodex’.

hbase(main):006:0> revoke 'Howcodex'

user_permission

This command is used to list all the permissions for a particular table. The syntax of user_permission is as follows:

hbase>user_permission ‘tablename’

The following code lists all the user permissions of ‘emp’ table.

hbase(main):013:0> user_permission 'emp'