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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.cassandra.db;
import java.nio.ByteBuffer;
import org.apache.cassandra.db.context.CounterContext;
public abstract class Conflicts
{
private Conflicts() {}
public enum Resolution { LEFT_WINS, MERGE, RIGHT_WINS };
public static Resolution resolveRegular(long leftTimestamp,
boolean leftLive,
int leftLocalDeletionTime,
ByteBuffer leftValue,
long rightTimestamp,
boolean rightLive,
int rightLocalDeletionTime,
ByteBuffer rightValue)
{
if (leftTimestamp != rightTimestamp)
return leftTimestamp < rightTimestamp ? Resolution.RIGHT_WINS : Resolution.LEFT_WINS;
if (leftLive != rightLive)
return leftLive ? Resolution.RIGHT_WINS : Resolution.LEFT_WINS;
int c = leftValue.compareTo(rightValue);
if (c < 0)
return Resolution.RIGHT_WINS;
else if (c > 0)
return Resolution.LEFT_WINS;
// Prefer the longest ttl if relevant
return leftLocalDeletionTime < rightLocalDeletionTime ? Resolution.RIGHT_WINS : Resolution.LEFT_WINS;
}
public static Resolution resolveCounter(long leftTimestamp,
boolean leftLive,
ByteBuffer leftValue,
long rightTimestamp,
boolean rightLive,
ByteBuffer rightValue)
{
// No matter what the counter cell's timestamp is, a tombstone always takes precedence. See CASSANDRA-7346.
if (!leftLive)
// left is a tombstone: it has precedence over right if either right is not a tombstone, or left has a greater timestamp
return rightLive || leftTimestamp > rightTimestamp ? Resolution.LEFT_WINS : Resolution.RIGHT_WINS;
// If right is a tombstone, since left isn't one, it has precedence
if (!rightLive)
return Resolution.RIGHT_WINS;
// Handle empty values. Counters can't truly have empty values, but we can have a counter cell that temporarily
// has one on read if the column for the cell is not queried by the user due to the optimization of #10657. We
// thus need to handle this (see #11726 too).
if (!leftValue.hasRemaining())
return rightValue.hasRemaining() || leftTimestamp > rightTimestamp ? Resolution.LEFT_WINS : Resolution.RIGHT_WINS;
if (!rightValue.hasRemaining())
return Resolution.RIGHT_WINS;
return Resolution.MERGE;
}
public static ByteBuffer mergeCounterValues(ByteBuffer left, ByteBuffer right)
{
return CounterContext.instance().merge(left, right);
}
}