public VectorExpression[] getVectorExpressions(List<ExprNodeDesc> exprNodes, VectorExpressionDescriptor.Mode mode)
    throws HiveException {

    int i = 0;
    if (null == exprNodes) {
      return new VectorExpression[0];
    }
    VectorExpression[] ret = new VectorExpression[exprNodes.size()];
    for (ExprNodeDesc e : exprNodes) {
      ret[i++] = getVectorExpression(e, mode);
    }
    return ret;
  }
Frees up actually marked scract columns.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorizationContext.java