Connecting to Mapr-DB (M3) from a Java client

Question

I'm trying to interact with a MapR-DB table from a simple Java application that is running within a node of an M3 MapR cluster. It seems that I am able to connect to the cluster but apparently I am not able to connect to the table properly. This is a snippet from the code:

Configuration configuration = new Configuration();
configuration.set("hbase.zookeeper.quorum", "192.168.2.1,192.168.2.2,192.168.2.3");
configuration.set("hbase.zookeeper.property.clientPort", "5181");
configuration.set("mapr.htable.impl", "com.mapr.fs.MapRHTable");
configuration.set("hbase.table.namespace.mappings", "*:/user/mapr/");

configuration = HBaseConfiguration.create(configuration);

HConnection connection = HConnectionManager.createConnection(configuration);

System.out.println("Is Master running? " + connection.isMasterRunning());

String tableName = args[0];

HTable table = (HTable) connection.getTable(tableName.getBytes());

for (HColumnDescriptor columnFamily : table.getTableDescriptor().getColumnFamilies()) {
    System.out.println("Column family: " + columnFamily.getNameAsString());
}

I have a table that is called "/user/mapr/test_table" (I see it in the MapR Web Console and I can access it through hbase shell). Running the code with any reasonable parameter for the table name just returns this exception:

org.apache.hadoop.hbase.TableNotFoundException: /user/mapr/test_table
    at org.apache.hadoop.hbase.client.HConnectionManager$HConnectionImplementation.getHTableDescriptor(HConnectionManager.java:2750)
    at org.apache.hadoop.hbase.client.HTable.getTableDescriptor(HTable.java:701)
    at it.noovle.bigdata.hadoop.MaprDBLocalTest.main(MaprDBLocalTest.java:49)

• In several places I read that with MapR-DB it is not necessary to connect through Zookeeper. Is it true in general or only for M7? I am running M3 at the moment.
• Is there a specific way to address MapR-DB tables from the Java HBase API? In hbase shellI simply use '/user/mapr/test_table'.
• Someone can share a decent example of a running example for an M3 cluster?

Answer 1

MapR allows you, depending of your installation to use:

• HBase
• MapR-DB

The "name" of the table defines if this is a "MapR-DB" or "Hbase" table:

• full path (with /) is a MapR-DB table /apps/my_tables/users
• simple string is an Hbase table users

Then depending of the name of the table the way the client is reaching the cluster varies:

• MapR DB : will use CLDB (default would be server:7222)
• HBase : will use Zookeeper (default would be server:5181)

The client code does not change between MapR-DB or Hbase, only the table names and "configuration" change, what I mean for the configuration is:

1. You have to install and configure MapR Client
2. You have to be sure you put all the dependencies in your classpath (hadoop client, hbase-mapr client)

I have a small project available here

Answer 2

To connect to MapR-DB, you don't require to connect to Zookeeper. To open the table you have to provide absolute path. For e.g /user/mapr/test_table. Attaching a simple example below:

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.*;
import org.apache.hadoop.hbase.KeyValue;
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.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;

public class HBaseExample {
    public static void main(String[] args) throws IOException {
        Configuration config = HBaseConfiguration.create();
        HTable table = new HTable(config, "/user/mapr/test_table");
        Put p = new Put(Bytes.toBytes("row1"));
        p.add(Bytes.toBytes("cf1"), Bytes.toBytes("col2"),
                Bytes.toBytes("ABC"));

        table.put(p);
        Get g = new Get(Bytes.toBytes("row1"));
        Result r = table.get(g);
        byte[] value = r.getValue(Bytes.toBytes("cf1"),
                Bytes.toBytes("col2"));

        String valueStr = Bytes.toString(value);
        System.out.println("GET: " + valueStr);
        Scan s = new Scan();
        s.addColumn(Bytes.toBytes("cf1"), Bytes.toBytes("col2"));
        ResultScanner scanner = table.getScanner(s);
        try {
            for (Result rr = scanner.next(); rr != null; rr = scanner.next()) {
                System.out.println("Found row: " + rr);
            }

        } finally {
            scanner.close();
        }
    }
}

Here is the hbase-site.xml, it is taken from MapR sandbox.

-bash-4.1$ cat ./hbase/hbase-0.98.7/conf/hbase-site.xml
<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>
<configuration>

  <property>
    <name>hbase.rootdir</name>
    <value>maprfs:///hbase</value>
  </property>

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

  <property>
<name>hbase.zookeeper.quorum</name>
<value>maprdemo</value>
  </property>

  <property>
<name>hbase.zookeeper.property.clientPort</name>
<value>5181</value>
  </property>

  <property>
    <name>dfs.support.append</name>
    <value>true</value>
  </property>

  <property>
    <name>hbase.fsutil.maprfs.impl</name>
    <value>org.apache.hadoop.hbase.util.FSMapRUtils</value>
  </property>

  <property>
    <name>hbase.regionserver.handler.count</name>
    <value>30</value>
    <!-- default is 25 -->
  </property>

  <!-- uncomment this to enable fileclient logging
  <property>
    <name>fs.mapr.trace</name>
    <value>debug</value>
  </property>
  -->

  <!-- Allows file/db client to use 64 threads -->
  <property>
    <name>fs.mapr.threads</name>
    <value>64</value>
  </property>

</configuration>
-bash-4.1$