Communicate with HBase: Linux Shell, Java API for Client access

• HBase : Introduction

HBase is a type of "NoSQL" database which runs on top of Hadoop/HDFS clusters. It stores data in form of key-value pair on Hadoop distributed file system. Table schema contains number of column-family which contain  a few to hundreds of thousand or millions of column. HBase is well suited for huge data ( Tera bytes or Peta bytes or whatever you can generate today) with random read/write access. Each row contains a rowkey as identifier and can be accessed as version# when inserted multiple times. Column values are stored with TIMESTAMP, and TTL can also be set for any column-family.

• Linux Shell

Linux Shell allows an easy access to HBase. Open a Shell/Terminal  in  your Linux system (assuming HBase is already configured on your machine), and reach to your HBase installation folder. 

Try out these commands : 

• Start HBase

user@ubuntu~$bin/start-hbase.sh // to start hbase/HMaster 

user@ubuntu~$bin/hbase shell // to enter into HBase shell

• Create

hbase(main):003:0> create 'htable', 'cf' // table name:'htable' & column-family:'cf' - it is advised to have small column-family names usually 1 or 2 letter!!
0 row(s) in 1.2200 seconds.

• Put

hbase(main):004:0> put 'htable', 'rowkey1', 'cf:qualifier1', 'value1' // rowkey:'rowkey1' & column name:'qualifier1' & column value:'value1'
0 row(s) in 1.2200 seconds.

hbase(main):005:0> put 'htable', 'rowkey2', 'cf:qualifier1', 'value2' // inserted as next row.

hbase(main):006:0> put 'htable', 'rowkey1', 'cf:qualifier1', 'value3' // inserted as next version for rowkey:'rowkey1'

any number of column/qualifier can be created while inserting data, only column-family(s) are required at the time of Table schema design.

• Scan

hbase(main):007:0> scan 'htable' // list all Rows & Columns.
ROW        COLUMN+CELL
rowkey1       column=cf:qualifier1, timestamp=1288380747188, value=value3
rowkey2       column=cf:qualifier1, timestamp=1288380738440, value=value2
2 row(s) in 0.0590 seconds

Scan only fetches latest version for any row.

• Get

hbase(main):008:0> get 'htable', 'rowkey2' // get accepts table-name & rowkey
COLUMN      CELL
cf:qualifier1        timestamp=1288380738440, value=value2
1 row(s) in 0.0400 seconds

Number of shell commands are available to work with it. But stored procedure, cursor, triggers, functions are not available here as you can find in RDBMS.

• Java API for client

HBase API provide outside applications(desktop, web etc) to access HBase table using org.apache.hadoop.hbase.client package. 

• An Example Program taken from  http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/client/package-summary.html

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import java.io.IOException;

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.Put;

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.util.Bytes;

// Class that has nothing but a main.

// Does a Put, Get and a Scan against an hbase table.

public class MyLittleHBaseClient {

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

    // You need a configuration object to tell the client where to connect.

    // When you create a HBaseConfiguration, it reads in whatever you've set

    // into your hbase-site.xml and in hbase-default.xml, as long as these can

    // be found on the CLASSPATH

    Configuration config = HBaseConfiguration.create();

    // This instantiates an HTable object that connects you to

    // the "myLittleHBaseTable" table.

    HTable table = new HTable(config, "myLittleHBaseTable");

    // To add to a row, use Put.  A Put constructor takes the name of the row

    // you want to insert into as a byte array.  In HBase, the Bytes class has

    // utility for converting all kinds of java types to byte arrays.  In the

    // below, we are converting the String "myLittleRow" into a byte array to

    // use as a row key for our update. Once you have a Put instance, you can

    // adorn it by setting the names of columns you want to update on the row,

    // the timestamp to use in your update, etc.If no timestamp, the server

    // applies current time to the edits.

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

    // To set the value you'd like to update in the row 'myLittleRow', specify

    // the column family, column qualifier, and value of the table cell you'd

    // like to update.  The column family must already exist in your table

    // schema.  The qualifier can be anything.  All must be specified as byte

    // arrays as hbase is all about byte arrays.  Lets pretend the table

    // 'myLittleHBaseTable' was created with a family 'myLittleFamily'.

    p.add(Bytes.toBytes("myLittleFamily"), Bytes.toBytes("someQualifier"),

      Bytes.toBytes("Some Value"));

    // Once you've adorned your Put instance with all the updates you want to

    // make, to commit it do the following (The HTable#put method takes the

    // Put instance you've been building and pushes the changes you made into

    // hbase)

    table.put(p);

    // Now, to retrieve the data we just wrote. The values that come back are

    // Result instances. Generally, a Result is an object that will package up

    // the hbase return into the form you find most palatable.

    Get g = new Get(Bytes.toBytes("myLittleRow"));

    Result r = table.get(g);

    byte [] value = r.getValue(Bytes.toBytes("myLittleFamily"),

      Bytes.toBytes("someQualifier"));

    // If we convert the value bytes, we should get back 'Some Value', the

    // value we inserted at this location.

    String valueStr = Bytes.toString(value);

    System.out.println("GET: " + valueStr);

    // Sometimes, you won't know the row you're looking for. In this case, you

    // use a Scanner. This will give you cursor-like interface to the contents

    // of the table.  To set up a Scanner, do like you did above making a Put

    // and a Get, create a Scan.  Adorn it with column names, etc.

    Scan s = new Scan();

    s.addColumn(Bytes.toBytes("myLittleFamily"), Bytes.toBytes("someQualifier"));

    ResultScanner scanner = table.getScanner(s);

    try {

      // Scanners return Result instances.

      // Now, for the actual iteration. One way is to use a while loop like so:

      for (Result rr = scanner.next(); rr != null; rr = scanner.next()) {

        // print out the row we found and the columns we were looking for

        System.out.println("Found row: " + rr);

      }

      // The other approach is to use a foreach loop. Scanners are iterable!

      // for (Result rr : scanner) {

      //   System.out.println("Found row: " + rr);

      // }

    } finally {

      // Make sure you close your scanners when you are done!

      // Thats why we have it inside a try/finally clause

      scanner.close();

    }

  }

}

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Above program automatically connects with local HBase configuration. To connect with  remote HBase machine, it requires path to 'hbase-site.xml' on Configuration.Path(path);

Apart from these two methods, HBase provides Thrift & REST gateways. Map Reduce programs can also read/write data to HBase clusters. 

will come with more in next post :)