simpledb.query
Class ProductPlan

java.lang.Object
  simpledb.query.ProductPlan

All Implemented Interfaces:

Plan

public class ProductPlan
extends java.lang.Object
implements Plan

The Plan class corresponding to the product relational algebra operator.

Author:

Edward Sciore

Constructor Summary

ProductPlan(Plan p1, Plan p2)
Creates a new product node in the query tree, having the two specified subqueries.

Method Summary

int	blocksAccessed() Estimates the number of block accesses in the product.
int	distinctValues(java.lang.String fldname) Estimates the distinct number of field values in the product.
Scan	open() Creates a product scan for this query.
int	recordsOutput() Estimates the number of output records in the product.
Schema	schema() Returns the schema of the product, which is the union of the schemas of the underlying queries.

Methods inherited from class java.lang.Object

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

Constructor Detail

ProductPlan

public ProductPlan(Plan p1,
                   Plan p2)

Creates a new product node in the query tree, having the two specified subqueries.

Parameters:

p1 - the left-hand subquery

p2 - the right-hand subquery

Method Detail

open

public Scan open()

Creates a product scan for this query.

Specified by:

open in interface Plan

Returns:

a scan

See Also:

Plan.open()

blocksAccessed

public int blocksAccessed()

Estimates the number of block accesses in the product. The formula is:

 B(product(p1,p2)) = B(p1) + R(p1)*B(p2) 

Specified by:

blocksAccessed in interface Plan

Returns:

the estimated number of block accesses

See Also:

Plan.blocksAccessed()

recordsOutput

public int recordsOutput()

Estimates the number of output records in the product. The formula is:

 R(product(p1,p2)) = R(p1)*R(p2) 

Specified by:

recordsOutput in interface Plan

Returns:

the estimated number of output records

See Also:

Plan.recordsOutput()

distinctValues

public int distinctValues(java.lang.String fldname)

Estimates the distinct number of field values in the product. Since the product does not increase or decrease field values, the estimate is the same as in the appropriate underlying query.

Specified by:

distinctValues in interface Plan

Parameters:

fldname - the name of a field

Returns:

the estimated number of distinct field values in the output

See Also:

Plan.distinctValues(java.lang.String)

schema

public Schema schema()

Returns the schema of the product, which is the union of the schemas of the underlying queries.

Specified by:

schema in interface Plan

Returns:

the query's schema

See Also:

Plan.schema()