Source Code Cross Referenced for Undoable.java in  » Database-DBMS » db-derby-10.2 » org » apache » derby » iapi » store » raw » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Database DBMS » db derby 10.2 » org.apache.derby.iapi.store.raw 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:
003:           Derby - Class org.apache.derby.iapi.store.raw.Undoable
004:
005:           Licensed to the Apache Software Foundation (ASF) under one or more
006:           contributor license agreements.  See the NOTICE file distributed with
007:           this work for additional information regarding copyright ownership.
008:           The ASF licenses this file to you under the Apache License, Version 2.0
009:           (the "License"); you may not use this file except in compliance with
010:           the License.  You may obtain a copy of the License at
011:
012:              http://www.apache.org/licenses/LICENSE-2.0
013:
014:           Unless required by applicable law or agreed to in writing, software
015:           distributed under the License is distributed on an "AS IS" BASIS,
016:           WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
017:           See the License for the specific language governing permissions and
018:           limitations under the License.
019:
020:         */
021:
022:        package org.apache.derby.iapi.store.raw;
023:
024:        import org.apache.derby.iapi.error.StandardException;
025:
026:        import org.apache.derby.iapi.services.io.LimitObjectInput;
027:        import java.io.IOException;
028:
029:        /**
030:         An Undoable operation is an operation that changed the state of the RawStore
031:         in the context of a transaction and this change can be rolled back.
032:
033:         @see Transaction#logAndDo
034:         @see Compensation
035:         */
036:
037:        public interface Undoable extends Loggable {
038:
039:            /**
040:            	Generate a loggable which will undo this change, using the optional
041:            	input if necessary.
042:
043:            	<P><B>NOTE</B><BR>Any logical undo logic must be hidden behind generateUndo.
044:            	During recovery redo, it should not depend on any logical undo logic.
045:
046:            	<P>
047:            	There are 3 ways to implement a redo-only log record:
048:            	<NL>
049:            	<LI>Make the log record a Loggable instead of an Undoable, this is the
050:            	cleanest method.
051:            	<LI>If you want to extend a log operation class that is an Undoable,
052:            	you can then either have generateUndo return null - this is preferred -
053:            	(the log operation's undoMe should never be called, so you can put a
054:            	null body there if the super class you are extending does not implement
055:            	a undoMe).
056:            	<LI>Or, have undoMe do nothing - this is least preferred.
057:            	</NL>
058:
059:            	<P>Any resource (e.g., latched page) that is needed for the
060:            	undoable.undoMe() must be acquired in undoable.generateUndo().
061:            	Moreover, that resource must be identified in the compensation
062:            	operation, and reacquired in the compensation.needsRedo() method during
063:            	recovery redo.
064:            	<BR><B>If you do write your own generateUndo or needsRedo, any
065:            	resource you latch or acquire, you must release them in
066:            	Compensation.doMe() or in Compensation.releaseResource().</B>
067:
068:            	<P> To write a generateUndo operation, find the object that needs to be
069:            	rolled back.  Assuming that it is a page, latch it, put together a
070:            	Compensation operation with the undoOp set to this operation, and save
071:            	the page number in the compensation operation, then
072:            	return the Compensation operation to the logging system.
073:
074:            	<P>
075:            	The sequence of events in a rollback of a undoable operation is
076:            	<NL>
077:            	<LI> The logging system calls undoable.generateUndo.  If this returns
078:            	null, then there is nothing to undo.
079:            	<LI> If generateUndo returns a Compensation operation, then the logging
080:            	system will log the Compensation log record and call
081:            	Compenstation.doMe().  (Hopefully, this just calls the undoable's
082:            	undoMe)
083:            	<LI> After the Compensation operation has been applied, the logging
084:            	system will call compensation.releaseResource(). If you do overwrite a
085:            	super class's releaseResource(), it would be prudent to call
086:            	super.releaseResource() first.
087:            	</NL>
088:
089:            	<P> The available() method of in indicates how much data can be read, i.e.
090:            	how much was originally written.
091:
092:            	@param xact	the transaction doing the rollback
093:            	@return the compensation operation that will rollback this change, or
094:            	null if nothing to undo. 
095:
096:            	@exception IOException Can be thrown by any of the methods of ObjectInput.
097:            	@exception StandardException Standard Cloudscape policy.
098:
099:            	@see Loggable#releaseResource
100:            	@see Loggable#needsRedo
101:
102:             */
103:            public Compensation generateUndo(Transaction xact,
104:                    LimitObjectInput in) throws StandardException, IOException;
105:
106:        }
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