[HBASE-1856] HBASE-1765 broke MapReduce when using Result.list()

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 0.20.1, 0.90.0
• Fix Version/s: 0.20.1
• Hadoop Flags: Reviewed
• Assignee: Lars George
• Reporter: Lars George
• Created: 22/Sep/09 08:31
• Updated: 20/Nov/15 13:01
• Resolved: 22/Sep/09 18:49

Description

Not sure if it is just me, but using MR over HBase employing a TableReducer is not working. After the first row is read all subsequent rows get the same Result's of that very first row. After tracing this from the Map phase I found the culprit in Result and the HBASE-1765 delayed field parsing change.

This is the code I use in the reduce():

   @Override
    protected void reduce(ImmutableBytesWritable key, Iterable<Result> values,
        Context context) throws IOException, InterruptedException {
      String skey = Bytes.toString(key.get());
      context.getCounter(CountersTotals.ROWS).increment(1);
      for (Result result : values) {
        for (KeyValue kv: result.list()) {
          try {
            if (LOG.isDebugEnabled()) LOG.debug("reduce: key -> " + skey + ", kv -> " + kv);
            ...

Here is the current list() implementation:

  public List<KeyValue> list() {
    if(this.kvs == null) {
      readFields();
    }
    return isEmpty()? null: Arrays.asList(sorted());
  }

The problem is that readFields(DataInput) does not clear kvs!

  public void readFields(final DataInput in)
  throws IOException {
    familyMap = null;
    row = null;
    int totalBuffer = in.readInt();
    if(totalBuffer == 0) {
      bytes = null;
      return;
    }
    byte [] raw = new byte[totalBuffer];
    in.readFully(raw, 0, totalBuffer);
    bytes = new ImmutableBytesWritable(raw, 0, totalBuffer);
  }

The above is called by the MR framework's WritableSerialization for each map output. But since "kvs" is already set "list()" returns the old data!

I assume the only change needed is clearing kvs as well:

  public void readFields(final DataInput in)
  throws IOException {
    familyMap = null;
    row = null;
    kvs = null;
    ....

I'll test that now and report.