- HBase : Introduction
- Linux Shell
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 secondsScan 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 secondsNumber 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
- 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 :)
