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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.Collections;
import java.util.List;
import javax.annotation.Nullable;
import org.apache.cassandra.db.ColumnFamilyStore;
import org.apache.cassandra.db.PartitionPosition;
import org.apache.cassandra.dht.Range;
import org.apache.cassandra.dht.Splitter;
import org.apache.cassandra.dht.Token;
public class ShardManagerDiskAware extends ShardManagerNoDisks
{
/**
* Positions for the disk boundaries, in covered token range. The last number defines the total token
* share owned by the node.
*/
private final double[] diskBoundaryPositions;
private final int[] diskStartRangeIndex;
private final List diskBoundaries;
public ShardManagerDiskAware(ColumnFamilyStore.VersionedLocalRanges localRanges, List diskBoundaries)
{
super(localRanges);
assert diskBoundaries != null && !diskBoundaries.isEmpty();
this.diskBoundaries = diskBoundaries;
double position = 0;
final List ranges = localRanges;
int diskIndex = 0;
diskBoundaryPositions = new double[diskBoundaries.size()];
diskStartRangeIndex = new int[diskBoundaryPositions.length];
diskStartRangeIndex[0] = 0;
for (int i = 0; i < localRangePositions.length; ++i)
{
Range range = ranges.get(i).range();
double weight = ranges.get(i).weight();
double span = localRangePositions[i] - position;
Token diskBoundary = diskBoundaries.get(diskIndex);
while (diskIndex < diskBoundaryPositions.length - 1 && (range.right.isMinimum() || diskBoundary.compareTo(range.right) < 0))
{
double leftPart = range.left.size(diskBoundary) * weight;
if (leftPart > span) // if the boundary falls on left or before it
leftPart = 0;
diskBoundaryPositions[diskIndex] = position + leftPart;
diskStartRangeIndex[diskIndex + 1] = i;
++diskIndex;
diskBoundary = diskBoundaries.get(diskIndex);
}
position += span;
}
diskBoundaryPositions[diskIndex] = position;
assert diskIndex + 1 == diskBoundaryPositions.length : "Disk boundaries are not within local ranges";
}
@Override
public double shardSetCoverage()
{
return localSpaceCoverage() / diskBoundaryPositions.length;
// The above is an approximation that works correctly for the normal allocation of disks.
// This can be properly calculated if a contained token is supplied as argument and the diskBoundaryPosition
// difference is retrieved for the disk containing that token.
// Unfortunately we don't currently have a way to get a representative position when an sstable writer is
// constructed for flushing.
}
/**
* Construct a boundary/shard iterator for the given number of shards.
*/
public ShardTracker boundaries(int shardCount)
{
return new BoundaryTrackerDiskAware(shardCount);
}
public class BoundaryTrackerDiskAware implements ShardTracker
{
private final int countPerDisk;
private double shardStep;
private double diskStart;
private int diskIndex;
private int nextShardIndex;
private int currentRange;
private Token currentStart;
@Nullable
private Token currentEnd; // null for the last shard
public BoundaryTrackerDiskAware(int countPerDisk)
{
this.countPerDisk = countPerDisk;
currentStart = localRanges.get(0).left();
diskIndex = -1;
}
void enterDisk(int diskIndex)
{
this.diskIndex = diskIndex;
currentRange = 0;
diskStart = diskIndex > 0 ? diskBoundaryPositions[diskIndex - 1] : 0;
shardStep = (diskBoundaryPositions[diskIndex] - diskStart) / countPerDisk;
nextShardIndex = 1;
}
private Token getEndToken(double toPos)
{
double left = currentRange > 0 ? localRangePositions[currentRange - 1] : 0;
double right = localRangePositions[currentRange];
while (toPos > right)
{
left = right;
right = localRangePositions[++currentRange];
}
final Range range = localRanges.get(currentRange).range();
return currentStart.getPartitioner().split(range.left, range.right, (toPos - left) / (right - left));
}
public Token shardStart()
{
return currentStart;
}
public Token shardEnd()
{
return currentEnd;
}
public Range shardSpan()
{
return new Range<>(currentStart, currentEnd != null ? currentEnd : currentStart.minValue());
}
public double shardSpanSize()
{
return shardStep;
}
/**
* 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.
*/
public boolean advanceTo(Token nextToken)
{
if (diskIndex < 0)
{
int search = Collections.binarySearch(diskBoundaries, nextToken);
if (search < 0)
search = -1 - search;
// otherwise (on equal) we are good as ranges are end-inclusive
enterDisk(search);
setEndToken();
}
if (currentEnd == null || nextToken.compareTo(currentEnd) <= 0)
return false;
do
{
currentStart = currentEnd;
if (nextShardIndex == countPerDisk)
enterDisk(diskIndex + 1);
else
++nextShardIndex;
setEndToken();
}
while (!(currentEnd == null || nextToken.compareTo(currentEnd) <= 0));
return true;
}
private void setEndToken()
{
if (nextShardIndex == countPerDisk)
{
if (diskIndex + 1 == diskBoundaryPositions.length)
currentEnd = null;
else
currentEnd = diskBoundaries.get(diskIndex);
}
else
currentEnd = getEndToken(diskStart + shardStep * nextShardIndex);
}
public int count()
{
return countPerDisk;
}
/**
* 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.
*/
public double fractionInShard(Range targetSpan)
{
Range shardSpan = shardSpan();
Range covered = targetSpan.intersectionNonWrapping(shardSpan);
if (covered == null)
return 0;
if (covered == targetSpan)
return 1;
double inShardSize = covered == shardSpan ? shardSpanSize() : ShardManagerDiskAware.this.rangeSpanned(covered);
double totalSize = ShardManagerDiskAware.this.rangeSpanned(targetSpan);
return inShardSize / totalSize;
}
public double rangeSpanned(PartitionPosition first, PartitionPosition last)
{
return ShardManagerDiskAware.this.rangeSpanned(first, last);
}
public int shardIndex()
{
return nextShardIndex - 1;
}
}
}