Creating a Table

Function Description

HBase allows you to create a table using the createTable method of the org.apache.hadoop.hbase.client.Admin object. You need to specify a table name and a column family name. You can create a table by using either of the following methods, but the latter one is recommended.

• Quickly create a table. A newly created table contains only one region, which will be automatically split into multiple new regions as data increases.
• Create a table using pre-assigned regions. You can pre-assign multiple regions before creating a table. This mode accelerates data write at the beginning of massive data write.

The column name and column family name of a table consist of letters, digits, and underscores (_) but cannot contain any special characters.

Sample Code

The following code snippets are in the testCreateTable method in the HBaseSample class of the com.huawei.bigdata.hbase.examples packet.

public static void testCreateTable() {
    LOG.info("Entering testCreateTable.");
    // Specify the table descriptor.
    HTableDescriptor htd = new HTableDescriptor(tableName);

    // Set the column family name to info.
    HColumnDescriptor hcd = new HColumnDescriptor("info");

    // Set data encoding methods.HBase provides DIFF,FAST_DIFF,PREFIX
    // and PREFIX_TREE
    hcd.setDataBlockEncoding(DataBlockEncoding.FAST_DIFF);

    // Set compression methods,HBase provides two default compression
    // methods:GZ and SNAPPY
    // GZ has the highest compression rate,but low compression and
    // decompression effeciency,fit for cold data
    // SNAPPY has low compression rate, but high compression and
    // decompression effeciency,fit for hot data.
    // it is advised to use SANPPY
    hcd.setCompressionType(Compression.Algorithm.SNAPPY);

    htd.addFamily(hcd);

    Admin admin = null;
    try {
        // Instantiate an Admin object.
        admin = conn.getAdmin();
        if (!admin.tableExists(tableName)) {
            LOG.info("Creating table...");
            // create table
            admin.createTable(htd);
            LOG.info(admin.getClusterStatus());
            LOG.info(admin.listNamespaceDescriptors());
            LOG.info("Table created successfully.");
        } else {
            LOG.warn("table already exists");
        }
    } catch (IOException e) {
        LOG.error("Create table failed.", e);
    } finally {
        if (admin != null) {
            try {
                // Close the Admin object.
                admin.close();
            } catch (IOException e) {
                LOG.error("Failed to close admin ", e);
            }
        }
    }
    LOG.info("Exiting testCreateTable.");
}