[HBASE-14267] In Mapreduce on HBase scenario, restart in TableInputFormat will result in getting wrong data.

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Abandoned
• Component/s: Client, mapreduce
• Assignee: Unassigned
• Reporter: Qianxi Zhang
• Created: 20/Aug/15 08:14
• Updated: 01/Jul/22 21:00
• Resolved: 01/Jul/22 21:00

Description

When I run a mapreduce job on HBase, I will modify the row got from Result.getRow(), for example, reverse the row. Since my program is very complicated to handle data, it takes long time, and the lease int Region server expired.
Result#195

  public byte [] getRow() {
    if (this.row == null) {
      this.row = (this.cells == null || this.cells.length == 0) ?
          null :
          CellUtil.cloneRow(this.cells[0]);
    }
    return this.row;
  }

TableInputFormat will restart the scan from last row, but the row has been modified, so it will read wrong data.
TableRecordReaderImpl#218

      } catch (IOException e) {
        // do not retry if the exception tells us not to do so
        if (e instanceof DoNotRetryIOException) {
          throw e;
        }
        // try to handle all other IOExceptions by restarting
        // the scanner, if the second call fails, it will be rethrown
        LOG.info("recovered from " + StringUtils.stringifyException(e));
        if (lastSuccessfulRow == null) {
          LOG.warn("We are restarting the first next() invocation," +
              " if your mapper has restarted a few other times like this" +
              " then you should consider killing this job and investigate" +
              " why it's taking so long.");
        }
        if (lastSuccessfulRow == null) {
          restart(scan.getStartRow());
        } else {
          restart(lastSuccessfulRow);
          scanner.next();    // skip presumed already mapped row
        }
        value = scanner.next();
        if (value != null && value.isStale()) numStale++;
        numRestarts++;
      }
      if (value != null && value.size() > 0) {
        key.set(value.getRow());
        lastSuccessfulRow = key.get();
        return true;
      }