/**
   * Find entries in the queue that are ready to be cleaned.
   *
   * @return information on the entry in the queue.
   */
  public List<CompactionInfo> findReadyToClean() throws MetaException {
    Connection dbConn = getDbConn();
    List<CompactionInfo> rc = new ArrayList<CompactionInfo>();

    try {
      Statement stmt = dbConn.createStatement();
      String s =
          "select cq_id, cq_database, cq_table, cq_partition, "
              + "cq_type, cq_run_as from COMPACTION_QUEUE where cq_state = '"
              + READY_FOR_CLEANING
              + "'";
      LOG.debug("Going to execute query <" + s + ">");
      ResultSet rs = stmt.executeQuery(s);
      while (rs.next()) {
        CompactionInfo info = new CompactionInfo();
        info.id = rs.getLong(1);
        info.dbname = rs.getString(2);
        info.tableName = rs.getString(3);
        info.partName = rs.getString(4);
        switch (rs.getString(5).charAt(0)) {
          case MAJOR_TYPE:
            info.type = CompactionType.MAJOR;
            break;
          case MINOR_TYPE:
            info.type = CompactionType.MINOR;
            break;
          default:
            throw new MetaException("Unexpected compaction type " + rs.getString(5));
        }
        info.runAs = rs.getString(6);
        rc.add(info);
      }
      LOG.debug("Going to rollback");
      dbConn.rollback();
      return rc;
    } catch (SQLException e) {
      LOG.error("Unable to select next element for cleaning, " + e.getMessage());
      try {
        LOG.debug("Going to rollback");
        dbConn.rollback();
      } catch (SQLException e1) {
      }
      throw new MetaException(
          "Unable to connect to transaction database " + StringUtils.stringifyException(e));
    } finally {
      closeDbConn(dbConn);
    }
  }
  /**
   * This will grab the next compaction request off of the queue, and assign it to the worker.
   *
   * @param workerId id of the worker calling this, will be recorded in the db
   * @return an info element for this compaction request, or null if there is no work to do now.
   */
  public CompactionInfo findNextToCompact(String workerId) throws MetaException {
    try {
      Connection dbConn = getDbConn();
      CompactionInfo info = new CompactionInfo();

      try {
        Statement stmt = dbConn.createStatement();
        String s =
            "select cq_id, cq_database, cq_table, cq_partition, "
                + "cq_type from COMPACTION_QUEUE where cq_state = '"
                + INITIATED_STATE
                + "' for update";
        LOG.debug("Going to execute query <" + s + ">");
        ResultSet rs = stmt.executeQuery(s);
        if (!rs.next()) {
          LOG.debug("No compactions found ready to compact");
          dbConn.rollback();
          return null;
        }
        info.id = rs.getLong(1);
        info.dbname = rs.getString(2);
        info.tableName = rs.getString(3);
        info.partName = rs.getString(4);
        switch (rs.getString(5).charAt(0)) {
          case MAJOR_TYPE:
            info.type = CompactionType.MAJOR;
            break;
          case MINOR_TYPE:
            info.type = CompactionType.MINOR;
            break;
          default:
            throw new MetaException("Unexpected compaction type " + rs.getString(5));
        }

        // Now, update this record as being worked on by this worker.
        long now = System.currentTimeMillis();
        s =
            "update COMPACTION_QUEUE set cq_worker_id = '"
                + workerId
                + "', "
                + "cq_start = "
                + now
                + ", cq_state = '"
                + WORKING_STATE
                + "' where cq_id = "
                + info.id;
        LOG.debug("Going to execute update <" + s + ">");
        if (stmt.executeUpdate(s) != 1) {
          LOG.error("Unable to update compaction record");
          LOG.debug("Going to rollback");
          dbConn.rollback();
        }
        LOG.debug("Going to commit");
        dbConn.commit();
        return info;
      } catch (SQLException e) {
        LOG.error("Unable to select next element for compaction, " + e.getMessage());
        try {
          LOG.debug("Going to rollback");
          dbConn.rollback();
        } catch (SQLException e1) {
        }
        detectDeadlock(e, "findNextToCompact");
        throw new MetaException(
            "Unable to connect to transaction database " + StringUtils.stringifyException(e));
      } finally {
        closeDbConn(dbConn);
      }
    } catch (DeadlockException e) {
      return findNextToCompact(workerId);
    } finally {
      deadlockCnt = 0;
    }
  }