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/*
* 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.*;
import java.util.Map.Entry;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.Iterables;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.cassandra.db.ColumnFamilyStore;
import org.apache.cassandra.db.Directories;
import org.apache.cassandra.db.compaction.writers.CompactionAwareWriter;
import org.apache.cassandra.db.compaction.writers.SplittingSizeTieredCompactionWriter;
import org.apache.cassandra.db.lifecycle.LifecycleTransaction;
import org.apache.cassandra.exceptions.ConfigurationException;
import org.apache.cassandra.io.sstable.format.SSTableReader;
import org.apache.cassandra.schema.CompactionParams;
import org.apache.cassandra.utils.Pair;
import static com.google.common.collect.Iterables.filter;
public class SizeTieredCompactionStrategy extends AbstractCompactionStrategy
{
private static final Logger logger = LoggerFactory.getLogger(SizeTieredCompactionStrategy.class);
private static final Comparator,Double>> bucketsByHotnessComparator = new Comparator, Double>>()
{
public int compare(Pair, Double> o1, Pair, Double> o2)
{
int comparison = Double.compare(o1.right, o2.right);
if (comparison != 0)
return comparison;
// break ties by compacting the smallest sstables first (this will probably only happen for
// system tables and new/unread sstables)
return Long.compare(avgSize(o1.left), avgSize(o2.left));
}
private long avgSize(List sstables)
{
long n = 0;
for (SSTableReader sstable : sstables)
n += sstable.bytesOnDisk();
return n / sstables.size();
}
};
protected SizeTieredCompactionStrategyOptions sizeTieredOptions;
protected volatile int estimatedRemainingTasks;
@VisibleForTesting
protected final Set sstables = new HashSet<>();
public SizeTieredCompactionStrategy(ColumnFamilyStore cfs, Map options)
{
super(cfs, options);
this.estimatedRemainingTasks = 0;
this.sizeTieredOptions = new SizeTieredCompactionStrategyOptions(options);
}
private synchronized List getNextBackgroundSSTables(final int gcBefore)
{
// make local copies so they can't be changed out from under us mid-method
int minThreshold = cfs.getMinimumCompactionThreshold();
int maxThreshold = cfs.getMaximumCompactionThreshold();
Iterable candidates = filterSuspectSSTables(filter(cfs.getUncompactingSSTables(), sstables::contains));
List> buckets = getBuckets(createSSTableAndLengthPairs(candidates), sizeTieredOptions.bucketHigh, sizeTieredOptions.bucketLow, sizeTieredOptions.minSSTableSize);
logger.trace("Compaction buckets are {}", buckets);
estimatedRemainingTasks = getEstimatedCompactionsByTasks(cfs, buckets);
cfs.getCompactionStrategyManager().compactionLogger.pending(this, estimatedRemainingTasks);
List mostInteresting = mostInterestingBucket(buckets, minThreshold, maxThreshold);
if (!mostInteresting.isEmpty())
return mostInteresting;
// if there is no sstable to compact in standard way, try compacting single sstable whose droppable tombstone
// ratio is greater than threshold.
List sstablesWithTombstones = new ArrayList<>();
for (SSTableReader sstable : candidates)
{
if (worthDroppingTombstones(sstable, gcBefore))
sstablesWithTombstones.add(sstable);
}
if (sstablesWithTombstones.isEmpty())
return Collections.emptyList();
return Collections.singletonList(Collections.max(sstablesWithTombstones, SSTableReader.sizeComparator));
}
/**
* @param buckets list of buckets from which to return the most interesting, where "interesting" is the total hotness for reads
* @param minThreshold minimum number of sstables in a bucket to qualify as interesting
* @param maxThreshold maximum number of sstables to compact at once (the returned bucket will be trimmed down to this)
* @return a bucket (list) of sstables to compact
*/
public static List mostInterestingBucket(List> buckets, int minThreshold, int maxThreshold)
{
// skip buckets containing less than minThreshold sstables, and limit other buckets to maxThreshold sstables
final List, Double>> prunedBucketsAndHotness = new ArrayList<>(buckets.size());
for (List bucket : buckets)
{
Pair, Double> bucketAndHotness = trimToThresholdWithHotness(bucket, maxThreshold);
if (bucketAndHotness != null && bucketAndHotness.left.size() >= minThreshold)
prunedBucketsAndHotness.add(bucketAndHotness);
}
if (prunedBucketsAndHotness.isEmpty())
return Collections.emptyList();
Pair, Double> hottest = Collections.max(prunedBucketsAndHotness, bucketsByHotnessComparator);
return hottest.left;
}
/**
* Returns a (bucket, hotness) pair or null if there were not enough sstables in the bucket to meet minThreshold.
* If there are more than maxThreshold sstables, the coldest sstables will be trimmed to meet the threshold.
**/
@VisibleForTesting
static Pair, Double> trimToThresholdWithHotness(List bucket, int maxThreshold)
{
// Sort by sstable hotness (descending). We first build a map because the hotness may change during the sort.
final Map hotnessSnapshot = getHotnessMap(bucket);
Collections.sort(bucket, new Comparator()
{
public int compare(SSTableReader o1, SSTableReader o2)
{
return -1 * Double.compare(hotnessSnapshot.get(o1), hotnessSnapshot.get(o2));
}
});
// and then trim the coldest sstables off the end to meet the maxThreshold
List prunedBucket = bucket.subList(0, Math.min(bucket.size(), maxThreshold));
// bucket hotness is the sum of the hotness of all sstable members
double bucketHotness = 0.0;
for (SSTableReader sstr : prunedBucket)
bucketHotness += hotness(sstr);
return Pair.create(prunedBucket, bucketHotness);
}
private static Map getHotnessMap(Collection sstables)
{
Map hotness = new HashMap<>(sstables.size());
for (SSTableReader sstable : sstables)
hotness.put(sstable, hotness(sstable));
return hotness;
}
/**
* Returns the reads per second per key for this sstable, or 0.0 if the sstable has no read meter
*/
private static double hotness(SSTableReader sstr)
{
// system tables don't have read meters, just use 0.0 for the hotness
return sstr.getReadMeter() == null ? 0.0 : sstr.getReadMeter().twoHourRate() / sstr.estimatedKeys();
}
@SuppressWarnings("resource")
public AbstractCompactionTask getNextBackgroundTask(int gcBefore)
{
List previousCandidate = null;
while (true)
{
List hottestBucket = getNextBackgroundSSTables(gcBefore);
if (hottestBucket.isEmpty())
return null;
// Already tried acquiring references without success. It means there is a race with
// the tracker but candidate SSTables were not yet replaced in the compaction strategy manager
if (hottestBucket.equals(previousCandidate))
{
logger.warn("Could not acquire references for compacting SSTables {} which is not a problem per se," +
"unless it happens frequently, in which case it must be reported. Will retry later.",
hottestBucket);
return null;
}
LifecycleTransaction transaction = cfs.getTracker().tryModify(hottestBucket, OperationType.COMPACTION);
if (transaction != null)
return new CompactionTask(cfs, transaction, gcBefore);
previousCandidate = hottestBucket;
}
}
@SuppressWarnings("resource")
public synchronized Collection getMaximalTask(final int gcBefore, boolean splitOutput)
{
Iterable filteredSSTables = filterSuspectSSTables(sstables);
if (Iterables.isEmpty(filteredSSTables))
return null;
LifecycleTransaction txn = cfs.getTracker().tryModify(filteredSSTables, OperationType.COMPACTION);
if (txn == null)
return null;
if (splitOutput)
return Arrays.asList(new SplittingCompactionTask(cfs, txn, gcBefore));
return Arrays.asList(new CompactionTask(cfs, txn, gcBefore));
}
@SuppressWarnings("resource")
public AbstractCompactionTask getUserDefinedTask(Collection sstables, final int gcBefore)
{
assert !sstables.isEmpty(); // checked for by CM.submitUserDefined
LifecycleTransaction transaction = cfs.getTracker().tryModify(sstables, OperationType.COMPACTION);
if (transaction == null)
{
logger.trace("Unable to mark {} for compaction; probably a background compaction got to it first. You can disable background compactions temporarily if this is a problem", sstables);
return null;
}
return new CompactionTask(cfs, transaction, gcBefore).setUserDefined(true);
}
public int getEstimatedRemainingTasks()
{
return estimatedRemainingTasks;
}
public static List> createSSTableAndLengthPairs(Iterable sstables)
{
List> sstableLengthPairs = new ArrayList<>(Iterables.size(sstables));
for(SSTableReader sstable : sstables)
sstableLengthPairs.add(Pair.create(sstable, sstable.onDiskLength()));
return sstableLengthPairs;
}
/*
* Group files of similar size into buckets.
*/
public static List> getBuckets(Collection> files, double bucketHigh, double bucketLow, long minSSTableSize)
{
// Sort the list in order to get deterministic results during the grouping below
List> sortedFiles = new ArrayList>(files);
Collections.sort(sortedFiles, new Comparator>()
{
public int compare(Pair p1, Pair p2)
{
return p1.right.compareTo(p2.right);
}
});
Map> buckets = new HashMap>();
outer:
for (Pair pair: sortedFiles)
{
long size = pair.right;
// look for a bucket containing similar-sized files:
// group in the same bucket if it's w/in 50% of the average for this bucket,
// or this file and the bucket are all considered "small" (less than `minSSTableSize`)
for (Entry> entry : buckets.entrySet())
{
List bucket = entry.getValue();
long oldAverageSize = entry.getKey();
if ((size > (oldAverageSize * bucketLow) && size < (oldAverageSize * bucketHigh))
|| (size < minSSTableSize && oldAverageSize < minSSTableSize))
{
// remove and re-add under new new average size
buckets.remove(oldAverageSize);
long totalSize = bucket.size() * oldAverageSize;
long newAverageSize = (totalSize + size) / (bucket.size() + 1);
bucket.add(pair.left);
buckets.put(newAverageSize, bucket);
continue outer;
}
}
// no similar bucket found; put it in a new one
ArrayList bucket = new ArrayList();
bucket.add(pair.left);
buckets.put(size, bucket);
}
return new ArrayList>(buckets.values());
}
public static int getEstimatedCompactionsByTasks(ColumnFamilyStore cfs, List> tasks)
{
int n = 0;
for (List bucket : tasks)
{
if (bucket.size() >= cfs.getMinimumCompactionThreshold())
n += Math.ceil((double)bucket.size() / cfs.getMaximumCompactionThreshold());
}
return n;
}
public long getMaxSSTableBytes()
{
return Long.MAX_VALUE;
}
public static Map validateOptions(Map options) throws ConfigurationException
{
Map uncheckedOptions = AbstractCompactionStrategy.validateOptions(options);
uncheckedOptions = SizeTieredCompactionStrategyOptions.validateOptions(options, uncheckedOptions);
uncheckedOptions.remove(CompactionParams.Option.MIN_THRESHOLD.toString());
uncheckedOptions.remove(CompactionParams.Option.MAX_THRESHOLD.toString());
return uncheckedOptions;
}
@Override
public boolean shouldDefragment()
{
return true;
}
@Override
public synchronized void addSSTable(SSTableReader added)
{
sstables.add(added);
}
@Override
public synchronized void removeSSTable(SSTableReader sstable)
{
sstables.remove(sstable);
}
public String toString()
{
return String.format("SizeTieredCompactionStrategy[%s/%s]",
cfs.getMinimumCompactionThreshold(),
cfs.getMaximumCompactionThreshold());
}
private static class SplittingCompactionTask extends CompactionTask
{
public SplittingCompactionTask(ColumnFamilyStore cfs, LifecycleTransaction txn, int gcBefore)
{
super(cfs, txn, gcBefore);
}
@Override
public CompactionAwareWriter getCompactionAwareWriter(ColumnFamilyStore cfs,
Directories directories,
LifecycleTransaction txn,
Set nonExpiredSSTables)
{
return new SplittingSizeTieredCompactionWriter(cfs, directories, txn, nonExpiredSSTables);
}
}
}
