vticosting.java

derby database source code.good for you.

/*

   Derby - Class org.apache.derby.vti.VTICosting

   Copyright 1999, 2004 The Apache Software Foundation or its licensors, as applicable.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

 */

package org.apache.derby.vti;

import java.sql.SQLException;

/**
  *	VTICosting is the interface that the query optimizer uses
  * to cost VTIs.
  * 
  The methods on the interface provide the optimizer
  * with the following information:
  <UL> 
  <LI> the estimated number of rows returned by the VTI in a single instantiation.
  <LI> the estimated cost to instantiate and iterate through the VTI.
  <LI> whether or not the VTI can be instantiated multiple times within a single query execution
  </UL>
  * <P>
  * This class can only be used within an SQL-J statement.  Using the methods
  * in application-side Java code results in Exceptions being thrown.
  *
  * @see org.apache.derby.vti.VTIEnvironment
 */
public interface VTICosting
{
	/**
	 * A useful constant: the default estimated number of rows returned by a VTI.
	 */
	public static final double defaultEstimatedRowCount		= 10000d;
	/**
	   A useful constant: The default estimated cost of instantiating and iterating throught a VTI.
	 */
	public static final double defaultEstimatedCost			= 100000d;

	/**
	 *  Get the estimated row count for a single scan of a VTI.
	 *
	 *  @param vtiEnvironment The VTIEnvironment.
	 *
	 *  @return	The estimated row count for a single scan of a VTI.
	 *
	 *  @exception SQLException thrown if the costing fails.
	 */
	public double getEstimatedRowCount(VTIEnvironment vtiEnvironment)
		throws SQLException;

	/**
	 *  Get the estimated cost for a single instantiation of a VTI.
	 *
	 *  @param vtiEnvironment The VTIEnvironment.
	 *
	 *  @return	The estimated cost for a single instantiation of a VTI.
	 *
	 *  @exception SQLException thrown if the costing fails.
	 */
	public double getEstimatedCostPerInstantiation(VTIEnvironment vtiEnvironment)
		throws SQLException;

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

		 @param vtiEnvironment The VTIEnvironment.

		 @return	True if the ResultSet can be instantiated multiple times, false if
		 can only be instantiated once.

		 @exception SQLException thrown if the costing fails.
	 */
	public boolean supportsMultipleInstantiations(VTIEnvironment vtiEnvironment)
		throws SQLException;
}