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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.compaction;
import java.util.Set;
import javax.annotation.Nullable;
import org.apache.cassandra.db.PartitionPosition;
import org.apache.cassandra.dht.Range;
import org.apache.cassandra.dht.Token;
import org.apache.cassandra.io.sstable.format.SSTableReader;
import org.apache.cassandra.io.sstable.format.SSTableWriter;
public interface ShardTracker
{
Token shardStart();
@Nullable
Token shardEnd();
Range shardSpan();
double shardSpanSize();
/**
* Advance to the given token (e.g. before writing a key). Returns true if this resulted in advancing to a new
* shard, and false otherwise.
*/
boolean advanceTo(Token nextToken);
int count();
/**
* Returns the fraction of the given token range's coverage that falls within this shard.
* E.g. if the span covers two shards exactly and the current shard is one of them, it will return 0.5.
*/
double fractionInShard(Range targetSpan);
double rangeSpanned(PartitionPosition first, PartitionPosition last);
int shardIndex();
default long shardAdjustedKeyCount(Set sstables)
{
// Note: computationally non-trivial; can be optimized if we save start/stop shards and size per table.
long shardAdjustedKeyCount = 0;
for (SSTableReader sstable : sstables)
shardAdjustedKeyCount += sstable.estimatedKeys() * fractionInShard(ShardManager.coveringRange(sstable));
return shardAdjustedKeyCount;
}
default void applyTokenSpaceCoverage(SSTableWriter writer)
{
if (writer.getFirst() != null)
writer.setTokenSpaceCoverage(rangeSpanned(writer.getFirst(), writer.getLast()));
}
}
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