protected final Path getOutPath(int bucketId) {
    String fileName = AcidUtils.BUCKET_PREFIX + String.format(AcidUtils.BUCKET_DIGITS, bucketId);
    Path out = new Path(outPath, fileName);
    return out;
  }
Validates that each input path belongs to the same partition since each
mapper merges the input to a single output directory

@param inputPath - input path
ql/src/java/org/apache/hadoop/hive/ql/exec/AbstractFileMergeOperator.java