optimizablelist.java

来自「derby database source code.good for you.」· Java 代码 · 共 113 行

/*

   Derby - Class org.apache.derby.iapi.sql.compile.OptimizableList

   Copyright 1997, 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.iapi.sql.compile;

import org.apache.derby.iapi.error.StandardException;

import org.apache.derby.iapi.sql.dictionary.DataDictionary;

/**
 * OptimizableList provides services for optimizing a list of
 * Optimizables (tables) in a query.
 */

public interface OptimizableList {

	/**
	 *  Return the number of Optimizables in the list.
	 *
	 *  @return integer		The number of Optimizables in the list.
	 */
	public int size();

	/**
	 *  Return the nth Optimizable in the list.
	 *
	 *  @param n				"index" (0 based) into the list.
	 *
	 *  @return Optimizable		The nth Optimizables in the list.
	 */
	public Optimizable getOptimizable(int n);

	/**
	 * Set the nth Optimizable to the specified Optimizable.
	 *
	 *  @param n				"index" (0 based) into the list.
	 *  @param optimizable		New nth Optimizable.
	 *
	 *  @return Nothing.
	 */
	public void setOptimizable(int n, Optimizable optimizable);

	/** 
	 * Verify that the Properties list with optimizer overrides, if specified, is valid
	 *
	 * @param dDictionary	The DataDictionary to use.
	 *
	 * @return Nothing.
	 * @exception StandardException		Thrown on error
	 */
	public void verifyProperties(DataDictionary dDictionary) throws StandardException;

	/**
	 * Set the join order for this list of optimizables.  The join order is
	 * represented as an array of integers - each entry in the array stands
	 * for the order of the corresponding element in the list.  For example,
	 * a joinOrder of {2, 0, 1} means that the 3rd Optimizable in the list
	 * (element 2, since we are zero-based) is the first one in the join
	 * order, followed by the 1st element in the list, and finally by the
	 * 2nd element in the list.
	 *
	 * This method shuffles this OptimizableList to match the join order.
	 *
	 * Obviously, the size of the array must equal the number of elements in
	 * the array, and the values in the array must be between 0 and the
	 * number of elements in the array minus 1, and the values in the array
	 * must be unique.
	 */
	public void reOrder(int[] joinOrder);

	/**
	 * user can specify that s/he doesn't want statistics to be considered when
	 * optimizing the query.
	 */
	public boolean useStatistics();

	/**
	 * Tell whether the join order should be optimized.
	 */
	public boolean optimizeJoinOrder();

	/**
	 * Tell whether the join order is legal.
	 */
	public boolean legalJoinOrder(int numTablesInQuery);

	/**
	 * Init the access paths for these optimizables.
	 *
	 * @param optimizer The optimizer being used.
	 *
	 * @return Nothing.
	 */
	public void initAccessPaths(Optimizer optimizer);
}