hbase count

1. Enable AggregationClient coprocessor

You have two choices :

You can enable aggregation coprocessor on all your tables by adding the following lines tohbase-site.xml :

 <property>
   <name>hbase.coprocessor.user.region.classes</name>
   <value>org.apache.hadoop.hbase.coprocessor.AggregateImplementation</value>
 </property>

or ...you can enable coprocessor only on a table throught the HBase shell :

1. disable the table
hbase> disable 'mytable'

2. add the coprocessor
hbase> alter 'mytable', METHOD => 'table_att','coprocessor'=>'|org.apache.hadoop.hbase.coprocessor.AggregateImplementation||'

3. re-enable the table
hbase> enable 'mytable'

2. Increase RPC timeout (opt)

In some cases the following exception could be raised : 
java.net.SocketTimeoutException: Call to node2/55.37.68.154:60020 failed on socket timeout exception
On large table or if you are expecting slow I/O this might be necessary:

 <property>
   <name>hbase.rpc.timeout</name>
   <value>300000</value>
 </property>

n.b. : you can also specify this property directly in the client source code, see next section

3. ''RowCount' Snippet

public class MyAggregationClient {

    private static final byte[] TABLE_NAME = Bytes.toBytes("mytable");
    private static final byte[] CF = Bytes.toBytes("d");

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

        Configuration customConf = new Configuration();
        customConf.setStrings("hbase.zookeeper.quorum",
                "node0,node1,node2");
        // Increase RPC timeout, in case of a slow computation
        customConf.setLong("hbase.rpc.timeout", 600000);
        // Default is 1, set to a higher value for faster scanner.next(..)
        customConf.setLong("hbase.client.scanner.caching", 1000);
        Configuration configuration = HBaseConfiguration.create(customConf);
        AggregationClient aggregationClient = new AggregationClient(
                configuration);
        Scan scan = new Scan();
        scan.addFamily(CF);
        long rowCount = aggregationClient.rowCount(TABLE_NAME, null, scan);
        System.out.println("row count is " + rowCount);

    }
}