simpledb.multibuffer
Class MultiBufferProductPlan

java.lang.Object
  simpledb.multibuffer.MultiBufferProductPlan

All Implemented Interfaces:

Plan

public class MultiBufferProductPlan
extends Object
implements Plan

The Plan class for the muti-buffer version of the product operator.

Author:

Edward Sciore

Constructor Summary

MultiBufferProductPlan(Plan lhs, Plan rhs, Transaction tx)
Creates a product plan for the specified queries.

Method Summary

int	blocksAccessed() Returns an estimate of the number of block accesses required to execute the query.
int	distinctValues(String fldname) Estimates the distinct number of field values in the product.
Scan	open() A scan for this query is created and returned, as follows.
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

MultiBufferProductPlan

public MultiBufferProductPlan(Plan lhs,
                              Plan rhs,
                              Transaction tx)

Creates a product plan for the specified queries.

Parameters:

lhs - the plan for the LHS query

rhs - the plan for the RHS query

tx - the calling transaction

Method Detail

open

public Scan open()

A scan for this query is created and returned, as follows. First, the method materializes its RHS query. It then determines the optimal chunk size, based on the size of the materialized file and the number of available buffers. It creates a chunk plan for each chunk, saving them in a list. Finally, it creates a multiscan for this list of plans, and returns that scan.

Specified by:

open in interface Plan

Returns:

a scan

See Also:

Plan.open()

blocksAccessed

public int blocksAccessed()

Returns an estimate of the number of block accesses required to execute the query. The formula is:

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

where C(p2) is the number of chunks of p2. The method uses the current number of available buffers to calculate C(p2), and so this value may differ when the query scan is opened.

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(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()