public void freeMarkedScratchColumns() {
      if (markedScratchColumns == null) {
        throw new RuntimeException("Illegal call");
      }
      for (int i = 0; i < markedScratchColumns.length; i++) {
        if (markedScratchColumns[i]) {
          scratchColumnTrackWasUsed[i] = false;
        }
      }
      markedScratchColumns = null;
    }
Context class for vectorization execution.
Main role is to map column names to column indices and serves as a
factory class for building vectorized expressions out of descriptors.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorizationContext.java