com.bigdata.rdf.sparql.ast

Enum QueryOptimizerEnum

java.lang.Object

java.lang.Enum<QueryOptimizerEnum>

com.bigdata.rdf.sparql.ast.QueryOptimizerEnum

All Implemented Interfaces:

Serializable, Comparable<QueryOptimizerEnum>

public enum QueryOptimizerEnum
extends Enum<QueryOptimizerEnum>

The known query optimizers.

Version:

$Id$

Author:

Bryan Thompson

See Also:

QueryHints.OPTIMIZER

Enum Constant Summary

Enum Constants

Enum Constant and Description
None The query optimizer is disabled.
Runtime A runtime query optimizer based on sampling.
Static A query optimizer based on a static analysis of the query which relies on fast range counts for the basic graph patterns to estimate the cardinality of the different access paths.

Method Summary

Methods

Modifier and Type	Method and Description
static QueryOptimizerEnum	valueOf(String name) Returns the enum constant of this type with the specified name.
static QueryOptimizerEnum[]	values() Returns an array containing the constants of this enum type, in the order they are declared.

Methods inherited from class java.lang.Enum

clone, compareTo, equals, finalize, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

None

public static final QueryOptimizerEnum None

The query optimizer is disabled. The joins in the query will be evaluated in the order in which they are given. This may be used to compensate when the static query optimizer produces an inefficient join ordering.

Static

public static final QueryOptimizerEnum Static

A query optimizer based on a static analysis of the query which relies on fast range counts for the basic graph patterns to estimate the cardinality of the different access paths. This optimizer is fast but it can fail to order joins correctly as the error in the estimated cardinality of joins can grow exponentially in the number of joins in the query.

Runtime

public static final QueryOptimizerEnum Runtime

A runtime query optimizer based on sampling. The runtime query optimizer samples each of the access paths and each of the joins and builds out join paths in a breadth first manner until it finds a join ordering which is known to dominate the other possible join orderings. The runtime query optimizer takes into account the actual cardinality and correlation in the query and the data selected by that query. The runtime query optimizer can have slightly more overhead than the static query optimizer, but it never produces a bad join ordering and often identifies the best join ordering. For cases where the static query optimizer produces a bad join ordering, the runtime query optimizer can find join orderings which are orders of magnitude more efficient (10x or 100x). For long running joins, this can translates into a savings of minutes or hours.

Method Detail

values

public static QueryOptimizerEnum[] values()

Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows:

for (QueryOptimizerEnum c : QueryOptimizerEnum.values())
    System.out.println(c);

Returns:

an array containing the constants of this enum type, in the order they are declared

valueOf

public static QueryOptimizerEnum valueOf(String name)

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)

Parameters:

name - the name of the enum constant to be returned.

Returns:

the enum constant with the specified name

Throws:

IllegalArgumentException - if this enum type has no constant with the specified name

NullPointerException - if the argument is null