/** Clean up aborted transactions from txns that have no components in txn_components. */
 public void cleanEmptyAbortedTxns() throws MetaException {
   try {
     Connection dbConn = getDbConn();
     try {
       Statement stmt = dbConn.createStatement();
       String s =
           "select txn_id from TXNS where "
               + "txn_id not in (select tc_txnid from TXN_COMPONENTS) and "
               + "txn_state = '"
               + TXN_ABORTED
               + "'";
       LOG.debug("Going to execute query <" + s + ">");
       ResultSet rs = stmt.executeQuery(s);
       Set<Long> txnids = new HashSet<Long>();
       while (rs.next()) txnids.add(rs.getLong(1));
       if (txnids.size() > 0) {
         StringBuffer buf = new StringBuffer("delete from TXNS where txn_id in (");
         boolean first = true;
         for (long tid : txnids) {
           if (first) first = false;
           else buf.append(", ");
           buf.append(tid);
         }
         buf.append(")");
         LOG.debug("Going to execute update <" + buf.toString() + ">");
         int rc = stmt.executeUpdate(buf.toString());
         LOG.debug("Removed " + rc + " records from txns");
         LOG.debug("Going to commit");
         dbConn.commit();
       }
     } catch (SQLException e) {
       LOG.error("Unable to delete from txns table " + e.getMessage());
       LOG.debug("Going to rollback");
       try {
         dbConn.rollback();
       } catch (SQLException e1) {
       }
       detectDeadlock(e, "cleanEmptyAbortedTxns");
       throw new MetaException(
           "Unable to connect to transaction database " + StringUtils.stringifyException(e));
     } finally {
       closeDbConn(dbConn);
     }
   } catch (DeadlockException e) {
     cleanEmptyAbortedTxns();
   } finally {
     deadlockCnt = 0;
   }
 }
  /**
   * 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 remove an entry from the queue after it has been compacted.
   *
   * @param info info on the compaction entry to remove
   */
  public void markCleaned(CompactionInfo info) throws MetaException {
    try {
      Connection dbConn = getDbConn();
      try {
        Statement stmt = dbConn.createStatement();
        String s = "delete from COMPACTION_QUEUE where cq_id = " + info.id;
        LOG.debug("Going to execute update <" + s + ">");
        if (stmt.executeUpdate(s) != 1) {
          LOG.error("Unable to delete compaction record");
          LOG.debug("Going to rollback");
          dbConn.rollback();
        }

        // Remove entries from completed_txn_components as well, so we don't start looking there
        // again.
        s =
            "delete from COMPLETED_TXN_COMPONENTS where ctc_database = '"
                + info.dbname
                + "' and "
                + "ctc_table = '"
                + info.tableName
                + "'";
        if (info.partName != null) {
          s += " and ctc_partition = '" + info.partName + "'";
        }
        LOG.debug("Going to execute update <" + s + ">");
        if (stmt.executeUpdate(s) < 1) {
          LOG.error(
              "Expected to remove at least one row from completed_txn_components when "
                  + "marking compaction entry as clean!");
        }

        s =
            "select txn_id from TXNS, TXN_COMPONENTS where txn_id = tc_txnid and txn_state = '"
                + TXN_ABORTED
                + "' and tc_database = '"
                + info.dbname
                + "' and tc_table = '"
                + info.tableName
                + "'";
        if (info.partName != null) s += " and tc_partition = '" + info.partName + "'";
        LOG.debug("Going to execute update <" + s + ">");
        ResultSet rs = stmt.executeQuery(s);
        Set<Long> txnids = new HashSet<Long>();
        while (rs.next()) txnids.add(rs.getLong(1));
        if (txnids.size() > 0) {

          // Remove entries from txn_components, as there may be aborted txn components
          StringBuffer buf = new StringBuffer();
          buf.append("delete from TXN_COMPONENTS where tc_txnid in (");
          boolean first = true;
          for (long id : txnids) {
            if (first) first = false;
            else buf.append(", ");
            buf.append(id);
          }

          buf.append(") and tc_database = '");
          buf.append(info.dbname);
          buf.append("' and tc_table = '");
          buf.append(info.tableName);
          buf.append("'");
          if (info.partName != null) {
            buf.append(" and tc_partition = '");
            buf.append(info.partName);
            buf.append("'");
          }
          LOG.debug("Going to execute update <" + buf.toString() + ">");
          int rc = stmt.executeUpdate(buf.toString());
          LOG.debug("Removed " + rc + " records from txn_components");

          // Don't bother cleaning from the txns table.  A separate call will do that.  We don't
          // know here which txns still have components from other tables or partitions in the
          // table, so we don't know which ones we can and cannot clean.
        }

        LOG.debug("Going to commit");
        dbConn.commit();
      } catch (SQLException e) {
        try {
          LOG.error("Unable to delete from compaction queue " + e.getMessage());
          LOG.debug("Going to rollback");
          dbConn.rollback();
        } catch (SQLException e1) {
        }
        detectDeadlock(e, "markCleaned");
        throw new MetaException(
            "Unable to connect to transaction database " + StringUtils.stringifyException(e));
      } finally {
        closeDbConn(dbConn);
      }
    } catch (DeadlockException e) {
      markCleaned(info);
    } finally {
      deadlockCnt = 0;
    }
  }
  /**
   * 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;
    }
  }