org.vanilladb.core.query.algebra

Class ExplainPlan

java.lang.Object

org.vanilladb.core.query.algebra.ExplainPlan

All Implemented Interfaces:

Plan

public class ExplainPlan
extends Object
implements Plan

The Plan class corresponding to the explain relational algebra operator.

Constructor Summary

Constructors

Constructor and Description
ExplainPlan(Plan p) Creates a new explain node in the query tree, having the specified query.

Method Summary

Modifier and Type	Method and Description
long	blocksAccessed() Estimates the number of block accesses for answering explain query.
Histogram	histogram() Returns the histogram that approximates the distribution of the underlying query results.
Scan	open() Creates a explain scan for this query.
long	recordsOutput() Returns an estimate of the number of records in the query's output table.
Schema	schema() Returns the schema of the explain query, which has only one field "query-plan" of type varchar(500).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ExplainPlan

public ExplainPlan(Plan p)

Creates a new explain node in the query tree, having the specified query.

Parameters:

p - the underlying query plan

Method Detail

open

public Scan open()

Creates a explain scan for this query.

Specified by:

open in interface Plan

Returns:

a scan

See Also:

Plan.open()

blocksAccessed

public long blocksAccessed()

Estimates the number of block accesses for answering explain query.

Specified by:

blocksAccessed in interface Plan

Returns:

the estimated number of block accesses

See Also:

Plan.blocksAccessed()

schema

public Schema schema()

Returns the schema of the explain query, which has only one field "query-plan" of type varchar(500).

Specified by:

schema in interface Plan

Returns:

the query's schema

See Also:

Plan.schema()

histogram

public Histogram histogram()

Returns the histogram that approximates the distribution of the underlying query results.

Specified by:

histogram in interface Plan

Returns:

the histogram

See Also:

Plan.histogram()

recordsOutput

public long recordsOutput()

Description copied from interface: Plan

Returns an estimate of the number of records in the query's output table.

Specified by:

recordsOutput in interface Plan

Returns:

the estimated number of output records