public void trackMatch(int logicalSlotNum) {

    Preconditions.checkState(!isPartitioned);

    final int longWordIndex = logicalSlotNum / Long.SIZE;
    final long longBitMask = 1L << (logicalSlotNum % Long.SIZE);
    if ((longMatchFlags[longWordIndex] & longBitMask) != 0) {

      // Flag is already on.
      isFirstMatch = false;
    } else {
      longMatchFlags[longWordIndex] |= longBitMask;
      isFirstMatch = true;
    }
    if (partitionParent != null) {

      // Push match flag up.
      partitionParent.isFirstMatch = isFirstMatch;
    }
  }
Record which hash table slot entries had key matches for FULL OUTER MapJoin.
Supports partitioned match trackers for HybridHashTableContainer.
ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/MatchTracker.java