Class Expr

fe/src/main/java/org/apache/impala/analysis/Expr.java:66–2066

Root of the expr node hierarchy.

 * Root of the expr node hierarchy.
 */
abstract public class Expr extends TreeNode<Expr> implements ParseNode, Cloneable {
  private static final Logger LOG = LoggerFactory.getLogger(Expr.class);

  // Limits on the number of expr children and the depth of an expr tree. These maximum
  // values guard against crashes due to stack overflows (IMPALA-432) and were
  // experimentally determined to be safe.
  public static final int EXPR_CHILDREN_LIMIT = 10000;
  // The expr depth limit is mostly due to our recursive implementation of clone().
  public static final int EXPR_DEPTH_LIMIT = 1000;

  // Name of the function that needs to be implemented by every Expr that
  // supports negation.
  private static final String NEGATE_FN = "negate";

  // To be used where we cannot come up with a better estimate (selectivity_ is -1).
  public static final double DEFAULT_SELECTIVITY = 0.1;

  // The relative costs of different Exprs. These numbers are not intended as a precise
  // reflection of running times, but as simple heuristics for ordering Exprs from cheap
  // to expensive.
  // TODO(tmwarshall): Get these costs in a more principled way, eg. with a benchmark.
  public static final float ARITHMETIC_OP_COST = 1;
  public static final float BINARY_PREDICATE_COST = 1;
  public static final float VAR_LEN_BINARY_PREDICATE_COST = 5;
  public static final float COMPOUND_PREDICATE_COST = 1;
  public static final float FUNCTION_CALL_COST = 10;
  public static final float JAVA_FUNCTION_CALL_COST = 100;
  public static final float IS_NOT_EMPTY_COST = 1;
  public static final float IS_NULL_COST = 1;
  public static final float LIKE_COST = 10;
  public static final float LITERAL_COST = 1;
  public static final float SLOT_REF_COST = 1;
  public static final float TIMESTAMP_ARITHMETIC_COST = 5;
  public static final float UNKNOWN_COST = -1;

  // Arbitrary max exprs considered for constant propagation due to O(n^2) complexity.
  private static final int CONST_PROPAGATION_EXPR_LIMIT = 200;

  // To be used when estimating the cost of Exprs of type string where we don't otherwise
  // have an estimate of how long the strings produced by that Expr are.
  public static final int DEFAULT_AVG_STRING_LENGTH = 5;

  // returns true if an Expr is a non-analytic aggregate.
  public static final com.google.common.base.Predicate<Expr> IS_AGGREGATE =
      new com.google.common.base.Predicate<Expr>() {
        @Override
        public boolean apply(Expr arg) {
          return arg instanceof FunctionCallExpr &&
              ((FunctionCallExpr)arg).isAggregateFunction();
        }
      };

  // Returns true if an Expr is a NOT CompoundPredicate.
  public static final com.google.common.base.Predicate<Expr> IS_NOT_PREDICATE =
      new com.google.common.base.Predicate<Expr>() {
        @Override
        public boolean apply(Expr arg) {
          return arg instanceof CompoundPredicate &&