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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.aggregation;
import java.nio.ByteBuffer;
import java.util.List;
import org.apache.cassandra.cql3.selection.Selector;
import org.apache.cassandra.db.Clustering;
import org.apache.cassandra.db.ClusteringComparator;
import org.apache.cassandra.db.DecoratedKey;
import org.apache.cassandra.schema.ColumnMetadata;
import org.apache.cassandra.transport.ProtocolVersion;
/**
* A GroupMaker can be used to determine if some sorted rows belongs to the same group or not.
*/
public abstract class GroupMaker
{
/**
* GroupMaker that groups all the rows together.
*/
public static final GroupMaker GROUP_EVERYTHING = new GroupMaker()
{
public boolean isNewGroup(DecoratedKey partitionKey, Clustering clustering)
{
return false;
}
public boolean returnAtLeastOneRow()
{
return true;
}
};
public static GroupMaker newPkPrefixGroupMaker(ClusteringComparator comparator,
int clusteringPrefixSize,
GroupingState state)
{
return new PkPrefixGroupMaker(comparator, clusteringPrefixSize, state);
}
public static GroupMaker newPkPrefixGroupMaker(ClusteringComparator comparator, int clusteringPrefixSize)
{
return new PkPrefixGroupMaker(comparator, clusteringPrefixSize);
}
public static GroupMaker newSelectorGroupMaker(ClusteringComparator comparator,
int clusteringPrefixSize,
Selector selector,
List columns,
GroupingState state)
{
return new SelectorGroupMaker(comparator, clusteringPrefixSize, selector, columns, state);
}
public static GroupMaker newSelectorGroupMaker(ClusteringComparator comparator,
int clusteringPrefixSize,
Selector selector,
List columns)
{
return new SelectorGroupMaker(comparator, clusteringPrefixSize, selector, columns);
}
/**
* Checks if a given row belongs to the same group that the previous row or not.
*
* @param partitionKey the partition key.
* @param clustering the row clustering key
* @return true if the row belongs to the same group that the previous one, false
* otherwise.
*/
public abstract boolean isNewGroup(DecoratedKey partitionKey, Clustering clustering);
/**
* Specify if at least one row must be returned. If the selection is performing some aggregations on all the rows,
* one row should be returned even if no records were processed.
*
* @return true if at least one row must be returned, false otherwise.
*/
public boolean returnAtLeastOneRow()
{
return false;
}
private static class PkPrefixGroupMaker extends GroupMaker
{
/**
* The size of the clustering prefix used to make the groups
*/
protected final int clusteringPrefixSize;
/**
* The comparator used to compare the clustering prefixes.
*/
protected final ClusteringComparator comparator;
/**
* The last partition key seen
*/
protected ByteBuffer lastPartitionKey;
/**
* The last clustering seen
*/
protected Clustering lastClustering;
public PkPrefixGroupMaker(ClusteringComparator comparator, int clusteringPrefixSize, GroupingState state)
{
this(comparator, clusteringPrefixSize);
this.lastPartitionKey = state.partitionKey();
this.lastClustering = state.clustering;
}
public PkPrefixGroupMaker(ClusteringComparator comparator, int clusteringPrefixSize)
{
this.comparator = comparator;
this.clusteringPrefixSize = clusteringPrefixSize;
}
@Override
public boolean isNewGroup(DecoratedKey partitionKey, Clustering clustering)
{
ByteBuffer key = partitionKey.getKey();
// We are entering a new group if:
// - the partition key is a new one
// - the last clustering was not null and does not have the same prefix as the new clustering one
boolean isNew = !key.equals(lastPartitionKey)
|| lastClustering == null
|| comparator.compare(lastClustering, clustering, clusteringPrefixSize) != 0;
lastPartitionKey = key;
lastClustering = Clustering.STATIC_CLUSTERING == clustering ? null : clustering;
return isNew;
}
}
private static class SelectorGroupMaker extends PkPrefixGroupMaker
{
/**
* The selector used to build the groups.
*/
private final Selector selector;
/**
* The output of the selector call on the last clustering
*/
private ByteBuffer lastOutput;
private final Selector.InputRow input;
public SelectorGroupMaker(ClusteringComparator comparator,
int clusteringPrefixSize,
Selector selector,
List columns,
GroupingState state)
{
super(comparator, clusteringPrefixSize, state);
this.selector = selector;
this.input = new Selector.InputRow(ProtocolVersion.CURRENT, columns, false);
this.lastOutput = lastClustering == null ? null :
executeSelector(lastClustering.bufferAt(clusteringPrefixSize - 1));
}
public SelectorGroupMaker(ClusteringComparator comparator,
int clusteringPrefixSize,
Selector selector,
List columns)
{
super(comparator, clusteringPrefixSize);
this.selector = selector;
this.input = new Selector.InputRow(ProtocolVersion.CURRENT, columns, false);
}
@Override
public boolean isNewGroup(DecoratedKey partitionKey, Clustering clustering)
{
ByteBuffer output =
Clustering.STATIC_CLUSTERING == clustering ? null
: executeSelector(clustering.bufferAt(clusteringPrefixSize - 1));
ByteBuffer key = partitionKey.getKey();
// We are entering a new group if:
// - the partition key is a new one
// - the last clustering was not null and does not have the same prefix as the new clustering one
boolean isNew = !key.equals(lastPartitionKey)
|| lastClustering == null
|| comparator.compare(lastClustering, clustering, clusteringPrefixSize - 1) != 0
|| compareOutput(output) != 0;
lastPartitionKey = key;
lastClustering = Clustering.STATIC_CLUSTERING == clustering ? null : clustering;
lastOutput = output;
return isNew;
}
private int compareOutput(ByteBuffer output)
{
if (output == null)
return lastOutput == null ? 0 : -1;
if (lastOutput == null)
return 1;
return selector.getType().compare(output, lastOutput);
}
private ByteBuffer executeSelector(ByteBuffer argument)
{
input.add(argument);
// For computing groups we do not need to use the client protocol version.
selector.addInput(input);
ByteBuffer output = selector.getOutput(ProtocolVersion.CURRENT);
selector.reset();
input.reset(false);
return output;
}
}
}