VTICosting

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org.apache.derby.vti
Interface VTICosting

public interface VTICosting

VTICosting is the interface that the query optimizer uses to cost VTIs. The methods on the interface provide the optimizer with the following information:

the estimated number of rows returned by the VTI in a single instantiation.
the estimated cost to instantiate and iterate through the VTI.
whether or not the VTI can be instantiated multiple times within a single query execution

This class can only be used within an SQL-J statement. Using the methods in application-side Java code results in Exceptions being thrown.

IBM Corp reserves the right to change, rename, or remove this interface at any time.

Field Summary

static double defaultEstimatedCost
          A useful constant: The default estimated cost of instantiating and iterating throught a VTI.

static double defaultEstimatedRowCount
          A useful constant: the default estimated number of rows returned by a VTI.

Method Summary

double getEstimatedCostPerInstantiation(VTIEnvironment vtiEnvironment)
          Get the estimated cost for a single instantiation of a VTI.

double getEstimatedRowCount(VTIEnvironment vtiEnvironment)
          Get the estimated row count for a single scan of a VTI.

boolean supportsMultipleInstantiations(VTIEnvironment vtiEnvironment)
          Find out if the ResultSet of the VTI can be instantiated multiple times.

Field Detail

defaultEstimatedRowCount

public static final double defaultEstimatedRowCount

A useful constant: the default estimated number of rows returned by a VTI.

See Also:: Constant Field Values

defaultEstimatedCost

public static final double defaultEstimatedCost

A useful constant: The default estimated cost of instantiating and iterating throught a VTI.

See Also:: Constant Field Values

Method Detail

getEstimatedRowCount

public double getEstimatedRowCount(VTIEnvironment vtiEnvironment)
                            throws java.sql.SQLException

Get the estimated row count for a single scan of a VTI.

getEstimatedCostPerInstantiation

public double getEstimatedCostPerInstantiation(VTIEnvironment vtiEnvironment)
                                        throws java.sql.SQLException

Get the estimated cost for a single instantiation of a VTI.

supportsMultipleInstantiations

public boolean supportsMultipleInstantiations(VTIEnvironment vtiEnvironment)
                                       throws java.sql.SQLException

Find out if the ResultSet of the VTI can be instantiated multiple times.