private void renameColumn(
      String databaseName, String tableName, CatalogProtos.AlterColumnProto alterColumnProto) {
    HiveCatalogStoreClientPool.HiveCatalogStoreClient client = null;
    try {

      client = clientPool.getClient();
      Table table = client.getHiveClient().getTable(databaseName, tableName);
      List<FieldSchema> columns = table.getSd().getCols();

      for (final FieldSchema currentColumn : columns) {
        if (currentColumn.getName().equalsIgnoreCase(alterColumnProto.getOldColumnName())) {
          currentColumn.setName(alterColumnProto.getNewColumnName());
        }
      }
      client.getHiveClient().alter_table(databaseName, tableName, table);

    } catch (NoSuchObjectException nsoe) {
    } catch (Exception e) {
      throw new TajoInternalError(e);
    } finally {
      if (client != null) {
        client.release();
      }
    }
  }
  private boolean existColumn(
      final String databaseName, final String tableName, final String columnName)
      throws CatalogException {
    boolean exist = false;
    HiveCatalogStoreClientPool.HiveCatalogStoreClient client = null;

    try {

      client = clientPool.getClient();
      Table table = client.getHiveClient().getTable(databaseName, tableName);
      List<FieldSchema> columns = table.getSd().getCols();

      for (final FieldSchema currentColumn : columns) {
        if (currentColumn.getName().equalsIgnoreCase(columnName)) {
          exist = true;
        }
      }
      client.getHiveClient().alter_table(databaseName, tableName, table);

    } catch (NoSuchObjectException nsoe) {
    } catch (Exception e) {
      throw new TajoInternalError(e);
    } finally {
      if (client != null) {
        client.release();
      }
    }

    return exist;
  }
  @Override
  public final CatalogProtos.TableDescProto getTable(String databaseName, final String tableName)
      throws CatalogException {
    org.apache.hadoop.hive.ql.metadata.Table table = null;
    HiveCatalogStoreClientPool.HiveCatalogStoreClient client = null;
    Path path = null;
    String storeType = null;
    org.apache.tajo.catalog.Schema schema = null;
    KeyValueSet options = null;
    TableStats stats = null;
    PartitionMethodDesc partitions = null;

    //////////////////////////////////
    // set tajo table schema.
    //////////////////////////////////
    try {
      // get hive table schema
      try {
        client = clientPool.getClient();
        table = HiveCatalogUtil.getTable(client.getHiveClient(), databaseName, tableName);
        path = table.getPath();
      } catch (NoSuchObjectException nsoe) {
        throw new UndefinedTableException(tableName);
      } catch (Exception e) {
        throw new TajoInternalError(e);
      }

      // convert HiveCatalogStore field schema into tajo field schema.
      schema = new org.apache.tajo.catalog.Schema();

      List<FieldSchema> fieldSchemaList = table.getCols();
      boolean isPartitionKey = false;
      for (FieldSchema eachField : fieldSchemaList) {
        isPartitionKey = false;

        if (table.getPartitionKeys() != null) {
          for (FieldSchema partitionKey : table.getPartitionKeys()) {
            if (partitionKey.getName().equals(eachField.getName())) {
              isPartitionKey = true;
            }
          }
        }

        if (!isPartitionKey) {
          String fieldName =
              databaseName
                  + CatalogConstants.IDENTIFIER_DELIMITER
                  + tableName
                  + CatalogConstants.IDENTIFIER_DELIMITER
                  + eachField.getName();
          TajoDataTypes.Type dataType =
              HiveCatalogUtil.getTajoFieldType(eachField.getType().toString());
          schema.addColumn(fieldName, dataType);
        }
      }

      // validate field schema.
      HiveCatalogUtil.validateSchema(table);

      stats = new TableStats();
      options = new KeyValueSet();
      options.putAll(table.getParameters());
      options.remove("EXTERNAL");

      Properties properties = table.getMetadata();
      if (properties != null) {
        // set field delimiter
        String fieldDelimiter = "", nullFormat = "";
        if (properties.getProperty(serdeConstants.FIELD_DELIM) != null) {
          fieldDelimiter = properties.getProperty(serdeConstants.FIELD_DELIM);
        } else {
          // if hive table used default row format delimiter, Properties doesn't have it.
          // So, Tajo must set as follows:
          fieldDelimiter = "\u0001";
        }

        // set null format
        if (properties.getProperty(serdeConstants.SERIALIZATION_NULL_FORMAT) != null) {
          nullFormat = properties.getProperty(serdeConstants.SERIALIZATION_NULL_FORMAT);
        } else {
          nullFormat = "\\N";
        }
        options.remove(serdeConstants.SERIALIZATION_NULL_FORMAT);

        // set file output format
        String fileOutputformat =
            properties.getProperty(hive_metastoreConstants.FILE_OUTPUT_FORMAT);
        storeType = HiveCatalogUtil.getStoreType(fileOutputformat);

        if (storeType.equalsIgnoreCase("TEXT")) {
          options.set(
              StorageConstants.TEXT_DELIMITER, StringEscapeUtils.escapeJava(fieldDelimiter));
          options.set(StorageConstants.TEXT_NULL, StringEscapeUtils.escapeJava(nullFormat));
        } else if (storeType.equals("RCFILE")) {
          options.set(StorageConstants.RCFILE_NULL, StringEscapeUtils.escapeJava(nullFormat));
          String serde = properties.getProperty(serdeConstants.SERIALIZATION_LIB);
          if (LazyBinaryColumnarSerDe.class.getName().equals(serde)) {
            options.set(StorageConstants.RCFILE_SERDE, StorageConstants.DEFAULT_BINARY_SERDE);
          } else if (ColumnarSerDe.class.getName().equals(serde)) {
            options.set(StorageConstants.RCFILE_SERDE, StorageConstants.DEFAULT_TEXT_SERDE);
          }
        } else if (storeType.equals("SEQUENCEFILE")) {
          options.set(
              StorageConstants.SEQUENCEFILE_DELIMITER,
              StringEscapeUtils.escapeJava(fieldDelimiter));
          options.set(StorageConstants.SEQUENCEFILE_NULL, StringEscapeUtils.escapeJava(nullFormat));
          String serde = properties.getProperty(serdeConstants.SERIALIZATION_LIB);
          if (LazyBinarySerDe.class.getName().equals(serde)) {
            options.set(StorageConstants.SEQUENCEFILE_SERDE, StorageConstants.DEFAULT_BINARY_SERDE);
          } else if (LazySimpleSerDe.class.getName().equals(serde)) {
            options.set(StorageConstants.SEQUENCEFILE_SERDE, StorageConstants.DEFAULT_TEXT_SERDE);
          }
        }

        // set data size
        long totalSize = 0;
        if (properties.getProperty("totalSize") != null) {
          totalSize = Long.parseLong(properties.getProperty("totalSize"));
        } else {
          try {
            FileSystem fs = path.getFileSystem(conf);
            if (fs.exists(path)) {
              totalSize = fs.getContentSummary(path).getLength();
            }
          } catch (IOException ioe) {
            throw new TajoInternalError(ioe);
          }
        }
        stats.setNumBytes(totalSize);
      }

      // set partition keys
      List<FieldSchema> partitionKeys = table.getPartitionKeys();

      if (null != partitionKeys) {
        org.apache.tajo.catalog.Schema expressionSchema = new org.apache.tajo.catalog.Schema();
        StringBuilder sb = new StringBuilder();
        if (partitionKeys.size() > 0) {
          for (int i = 0; i < partitionKeys.size(); i++) {
            FieldSchema fieldSchema = partitionKeys.get(i);
            TajoDataTypes.Type dataType =
                HiveCatalogUtil.getTajoFieldType(fieldSchema.getType().toString());
            String fieldName =
                databaseName
                    + CatalogConstants.IDENTIFIER_DELIMITER
                    + tableName
                    + CatalogConstants.IDENTIFIER_DELIMITER
                    + fieldSchema.getName();
            expressionSchema.addColumn(new Column(fieldName, dataType));
            if (i > 0) {
              sb.append(",");
            }
            sb.append(fieldSchema.getName());
          }
          partitions =
              new PartitionMethodDesc(
                  databaseName, tableName, PartitionType.COLUMN, sb.toString(), expressionSchema);
        }
      }
    } finally {
      if (client != null) client.release();
    }
    TableMeta meta = new TableMeta(storeType, options);
    TableDesc tableDesc = new TableDesc(databaseName + "." + tableName, schema, meta, path.toUri());
    if (table.getTableType().equals(TableType.EXTERNAL_TABLE)) {
      tableDesc.setExternal(true);
    }
    if (stats != null) {
      tableDesc.setStats(stats);
    }
    if (partitions != null) {
      tableDesc.setPartitionMethod(partitions);
    }
    return tableDesc.getProto();
  }