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/**

Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016.  All rights reserved.

Contact:
     SYSTAP, LLC DBA Blazegraph
     2501 Calvert ST NW #106
     Washington, DC 20008
     licenses@blazegraph.com

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.

This program 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 General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/
/*
 * Created on Oct 23, 2006
 */

package com.bigdata.btree.isolation;

import java.io.Serializable;

import com.bigdata.btree.IIndex;
import com.bigdata.btree.ITuple;
import com.bigdata.journal.Journal;
import com.bigdata.journal.Tx;

/**
 * 

* An interface invoked during backward validation when a write-write conflict * has been detected. The implementation must either resolve the write-write * conflict by returning a new version in which the conflict is resolved or * report an unresolvable conflict, in which case backward validation will force * the transaction to abort. *

* * @see http://www.cs.brown.edu/~mph/Herlihy90a/p96-herlihy.pdf for an excellent * discussion of data type specific state-based conflict resolution, * including examples for things such as bank accounts. * * @todo Write tests in which we do state-based conflict resolution for both the * bank account examples in Herlihy and the examples that we will find in * race conditions for the lexical terms and statements in an RDF model. * * @todo How to handle cascading dependencies. For example, if there is a * write-write conflict on the terms index of an RDF store then the * reverse index and any statements written in the transaction for the * term with which the write-write conflict exists must also be updated. * This will require lots of application knowledge and access to the * {@link Tx} object itself? * * @todo The burden of deserialization is on the application and its * implementation of this interface at present. Will object * deserialization be buffered by a cache? Cache integrity is tricky here * since the objects being reconciled belong to different transactional * states. I can see a situation in which conflict resolution requires * multiple changes in a graph structure, and could require simultaneous * traversal of both a read-only view of the last committed state on the * journal and a read-write view of the transaction. Resolution would then * proceed by WRITE or DELETE operations on the transaction. The method * signature would be changed to: * * This would have to allow READ,WRITE,and DELETE operations during PREPARE.
* * Handling distributed conflicts could also require awareness of the int64 * identifier. That is accessible to the caller if they have saved a reference * to the {@link Journal} in the constructor. Such resolution would have to be * network aware (i.e., aware that there was a distributed database).
* * If we change to allowing object graph traversals during conflict resolution, * then we need to closely consider whether cycles can form and how they will * ground out. * * @author Bryan Thompson * @version $Id$ */ public interface IConflictResolver extends Serializable { /** *

* Resolve a write-write conflict between a committed version on the journal * and the current version within a transaction that is validating. *

* * @param writeSet * The view on which conflict resolver must write the resolved * index entry. * * @param txTuple * The tuple written by the transaction that is being validated. * * @param currentTuple * The current tuple committed in the global state with which the * write-write conflict exists. * * @return true iff the conflict was resolved. */ public boolean resolveConflict(IIndex writeSet, ITuple txTuple, ITuple currentTuple) throws Exception; }




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