storeimpl.java

java 数据库 功能强大 效率高 SmallSQL Database is a free DBMS library for the Java(tm) platform. It runs on

/* =============================================================
 * SmallSQL : a free Java DBMS library for the Java(tm) platform
 * =============================================================
 *
 * (C) Copyright 2004-2007, by Volker Berlin.
 *
 * Project Info:  http://www.smallsql.de/
 *
 * This library is free software; you can redistribute it and/or modify it 
 * under the terms of the GNU Lesser General Public License as published by 
 * the Free Software Foundation; either version 2.1 of the License, or 
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but 
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, 
 * USA.  
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc. 
 * in the United States and other countries.]
 *
 * ---------------
 * StoreImpl.java
 * ---------------
 * Author: Volker Berlin
 * 
 */
package smallsql.database;

import java.io.*;
import java.sql.SQLException;


public class StoreImpl extends Store {

    private static final int DEFAULT_PAGE_SIZE = 8192; // 8 Kb
	private static final int PAGE_MAGIC = 0x12DD13DE; // are used for repairing a table
    /**
     * The structure of the Page Control Block is:
     * 4 byte - page magic
     * 4 Byte - Status 0:normal; 1:deleted; 2:Pointer to an update; 3: updated page
     * 4 Byte - used size of the page
     * 4 byte - physical size of the page
     * 4 byte - offset to the next page
     * 8 byte - position of an updated page
     */
	private static final int PAGE_CONTROL_SIZE = 28;
	private static final byte[] page_control = new byte[PAGE_CONTROL_SIZE]; 
	private int status; // valid value are follow:
	private static final int NORMAL = 0;
    private static final int DELETED = 1;
    /**
     * Using of UPDATE_POINTER and UPDATED_PAGE
     * 	If a page are updated and the new data are larger as the old data then
     *  the old page are changed to a UPDATE_POINTER. The new page is 
     *  a UPDATED_PAGE. On reading the pages only the UPDATE_POINTER is read.
     *  The UPDATED_PAGE are skipped. Thats a row change not it position.
     */
	private static final int UPDATE_POINTER = 2;
	private static final int UPDATED_PAGE = 3;
    
    final private Table table;
    private byte[] page; // Data of one page
    private StorePage storePage;
    private long filePos; // Position in the file
    private int sizeUsed;
    private int sizePhysical;
    private int nextPageOffset;
    private long filePosUpdated;
    private int type;
    
    private StoreImpl updatePointer;

    private StoreImpl( Table table, StorePage storePage, int type, long filePos ){
		this.table     = table;
		this.storePage    = storePage;
		this.filePos   = filePos;
		this.type      = type;
    }
    
    
    /** folgende Arten von StoreImpl Types sind m鰃lich
        INSERT: Eine Page die neue Daten enthalten wird. filePos ist noch nicht spezifiziert.
        CREATE: Eine spezielle Art von INSERT.
        SELECT: Nur Leseoperationen sind m鰃lich.
        UPDATE: Hat eine filePos, wenn neue gr鲞e zu klein, mu