Reading HBase Cold and Hot Separation Data Using the GET Command

Function Description

Before reading data from a table, create a table instance and a Get object. You can also set parameters for the Get object, such as the column family name and column name. Query results are stored in the Result object that stores multiple Cells.

For a column family with the cold and hot data separation feature enabled, you can choose to only query the cold or hot data by specifying parameters.

Sample Code

• The query that does not contain the HOT_ONLY hint may hit cold data.

  public void testGet() {
    LOG.info("Entering testGet.");
    // Specify the column family name.
    byte[] familyName = Bytes.toBytes("info");
    // Specify the column name.
    byte[][] qualifier = { Bytes.toBytes("temp"), Bytes.toBytes("hum") };
    // Specify RowKey.
    byte[] rowKey = Bytes.toBytes("Shenzhen#Longgang#2017/7/1 03:00:00");
    Table table = null;
    try {
      // Create the Table instance.
      table = conn.getTable(tableName);
      // Instantiate a Get object.
      Get get = new Get(rowKey);
      // Set the column family name and column name.
      get.addColumn(familyName, qualifier[0]);
      get.addColumn(familyName, qualifier[1]);
      // Submit a get request.
      Result result = table.get(get);
      // Print query results.
      for (Cell cell : result.rawCells()) {
        LOG.info(Bytes.toString(CellUtil.cloneRow(cell)) + ":"
            + Bytes.toString(CellUtil.cloneFamily(cell)) + ","
            + Bytes.toString(CellUtil.cloneQualifier(cell)) + ","
            + Bytes.toString(CellUtil.cloneValue(cell)));
      }
      LOG.info("Get data successfully.");
    } catch (IOException e) {
      LOG.error("Get data failed " ,e);
    } finally {
      if (table != null) {
        try {
          // Close the HTable object.
          table.close();
        } catch (IOException e) {
          LOG.error("Close table failed " ,e);
        }
      }
    }
    LOG.info("Exiting testGet.");
  } 

• The query that contains the HOT_ONLY hint hits only hot data.

  public void testGet() {
    LOG.info("Entering testGet.");
    // Specify the column family name.
    byte[] familyName = Bytes.toBytes("info");
    // Specify the column name.
    byte[][] qualifier = { Bytes.toBytes("temp"), Bytes.toBytes("hum") };
    // Specify RowKey.
    byte[] rowKey = Bytes.toBytes("Shenzhen#Longgang#2017/7/2 10:00:00");
    Table table = null;
    try {
      // Create the Table instance.
      table = conn.getTable(tableName);
      // Instantiate a Get object.
      Get get = new Get(rowKey);
      // Set HOT_ONLY.
      get.setAttribute(HBaseConstants.HOT_ONLY, Bytes.toBytes(true));
      // Set the column family name and column name.
      get.addColumn(familyName, qualifier[0]);
      get.addColumn(familyName, qualifier[1]);
      // Submit a get request.
      Result result = table.get(get);
      // Print query results.
      for (Cell cell : result.rawCells()) {
        LOG.info(Bytes.toString(CellUtil.cloneRow(cell)) + ":"
            + Bytes.toString(CellUtil.cloneFamily(cell)) + ","
            + Bytes.toString(CellUtil.cloneQualifier(cell)) + ","
            + Bytes.toString(CellUtil.cloneValue(cell)));
      }
      LOG.info("Get data successfully.");
    } catch (IOException e) {
      LOG.error("Get data failed " ,e);
    } finally {
      if (table != null) {
        try {
          // Close the HTable object.
          table.close();
        } catch (IOException e) {
          LOG.error("Close table failed " ,e);
        }
      }
    }
    LOG.info("Exiting testGet.");
  }