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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.io.sstable;
import java.io.IOException;
import java.lang.management.ManagementFactory;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import javax.management.MBeanServer;
import javax.management.ObjectName;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.Iterables;
import com.google.common.collect.Lists;
import com.google.common.collect.Multimap;
import com.google.common.collect.Sets;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.cassandra.concurrent.DebuggableScheduledThreadPoolExecutor;
import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.db.ColumnFamilyStore;
import org.apache.cassandra.db.DataTracker;
import org.apache.cassandra.db.Keyspace;
import org.apache.cassandra.utils.Pair;
import org.apache.cassandra.utils.WrappedRunnable;
import static org.apache.cassandra.io.sstable.Downsampling.BASE_SAMPLING_LEVEL;
/**
* Manages the fixed-size memory pool for index summaries, periodically resizing them
* in order to give more memory to hot sstables and less memory to cold sstables.
*/
public class IndexSummaryManager implements IndexSummaryManagerMBean
{
private static final Logger logger = LoggerFactory.getLogger(IndexSummaryManager.class);
public static final String MBEAN_NAME = "org.apache.cassandra.db:type=IndexSummaries";
public static final IndexSummaryManager instance;
private int resizeIntervalInMinutes = 0;
private long memoryPoolBytes;
// The target (or ideal) number of index summary entries must differ from the actual number of
// entries by this ratio in order to trigger an upsample or downsample of the summary. Because
// upsampling requires reading the primary index in order to rebuild the summary, the threshold
// for upsampling is is higher.
static final double UPSAMPLE_THRESHOLD = 1.5;
static final double DOWNSAMPLE_THESHOLD = 0.75;
private final DebuggableScheduledThreadPoolExecutor executor;
// our next scheduled resizing run
private ScheduledFuture future;
static
{
instance = new IndexSummaryManager();
MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
try
{
mbs.registerMBean(instance, new ObjectName(MBEAN_NAME));
}
catch (Exception e)
{
throw new RuntimeException(e);
}
}
private IndexSummaryManager()
{
executor = new DebuggableScheduledThreadPoolExecutor(1, "IndexSummaryManager", Thread.MIN_PRIORITY);
long indexSummarySizeInMB = DatabaseDescriptor.getIndexSummaryCapacityInMB();
int interval = DatabaseDescriptor.getIndexSummaryResizeIntervalInMinutes();
logger.info("Initializing index summary manager with a memory pool size of {} MB and a resize interval of {} minutes",
indexSummarySizeInMB, interval);
setMemoryPoolCapacityInMB(DatabaseDescriptor.getIndexSummaryCapacityInMB());
setResizeIntervalInMinutes(DatabaseDescriptor.getIndexSummaryResizeIntervalInMinutes());
}
public int getResizeIntervalInMinutes()
{
return resizeIntervalInMinutes;
}
public void setResizeIntervalInMinutes(int resizeIntervalInMinutes)
{
int oldInterval = this.resizeIntervalInMinutes;
this.resizeIntervalInMinutes = resizeIntervalInMinutes;
long initialDelay;
if (future != null)
{
initialDelay = oldInterval < 0
? resizeIntervalInMinutes
: Math.max(0, resizeIntervalInMinutes - (oldInterval - future.getDelay(TimeUnit.MINUTES)));
future.cancel(false);
}
else
{
initialDelay = resizeIntervalInMinutes;
}
if (this.resizeIntervalInMinutes < 0)
{
future = null;
return;
}
future = executor.scheduleWithFixedDelay(new WrappedRunnable()
{
protected void runMayThrow() throws Exception
{
redistributeSummaries();
}
}, initialDelay, resizeIntervalInMinutes, TimeUnit.MINUTES);
}
// for testing only
@VisibleForTesting
Long getTimeToNextResize(TimeUnit timeUnit)
{
if (future == null)
return null;
return future.getDelay(timeUnit);
}
public long getMemoryPoolCapacityInMB()
{
return memoryPoolBytes / 1024L / 1024L;
}
public Map getIndexIntervals()
{
List sstables = getAllSSTables();
Map intervals = new HashMap<>(sstables.size());
for (SSTableReader sstable : sstables)
intervals.put(sstable.getFilename(), (int) Math.round(sstable.getEffectiveIndexInterval()));
return intervals;
}
public double getAverageIndexInterval()
{
List sstables = getAllSSTables();
double total = 0.0;
for (SSTableReader sstable : sstables)
total += sstable.getEffectiveIndexInterval();
return total / sstables.size();
}
public void setMemoryPoolCapacityInMB(long memoryPoolCapacityInMB)
{
this.memoryPoolBytes = memoryPoolCapacityInMB * 1024L * 1024L;
}
/**
* Returns the actual space consumed by index summaries for all sstables.
* @return space currently used in MB
*/
public double getMemoryPoolSizeInMB()
{
long total = 0;
for (SSTableReader sstable : getAllSSTables())
total += sstable.getIndexSummaryOffHeapSize();
return total / 1024.0 / 1024.0;
}
private List getAllSSTables()
{
List result = new ArrayList<>();
for (Keyspace ks : Keyspace.all())
{
for (ColumnFamilyStore cfStore: ks.getColumnFamilyStores())
result.addAll(cfStore.getSSTables());
}
return result;
}
/**
* Returns a Pair of all compacting and non-compacting sstables. Non-compacting sstables will be marked as
* compacting.
*/
private Pair, Multimap> getCompactingAndNonCompactingSSTables()
{
List allCompacting = new ArrayList<>();
Multimap allNonCompacting = HashMultimap.create();
for (Keyspace ks : Keyspace.all())
{
for (ColumnFamilyStore cfStore: ks.getColumnFamilyStores())
{
Set nonCompacting, allSSTables;
do
{
allSSTables = cfStore.getDataTracker().getSSTables();
nonCompacting = Sets.newHashSet(cfStore.getDataTracker().getUncompactingSSTables(allSSTables));
}
while (!(nonCompacting.isEmpty() || cfStore.getDataTracker().markCompacting(nonCompacting)));
allNonCompacting.putAll(cfStore.getDataTracker(), nonCompacting);
allCompacting.addAll(Sets.difference(allSSTables, nonCompacting));
}
}
return Pair.create(allCompacting, allNonCompacting);
}
public void redistributeSummaries() throws IOException
{
Pair, Multimap> compactingAndNonCompacting = getCompactingAndNonCompactingSSTables();
try
{
redistributeSummaries(compactingAndNonCompacting.left, Lists.newArrayList(compactingAndNonCompacting.right.values()), this.memoryPoolBytes);
}
finally
{
for(DataTracker tracker : compactingAndNonCompacting.right.keySet())
tracker.unmarkCompacting(compactingAndNonCompacting.right.get(tracker));
}
}
/**
* Attempts to fairly distribute a fixed pool of memory for index summaries across a set of SSTables based on
* their recent read rates.
* @param nonCompacting a list of sstables to share the memory pool across
* @param memoryPoolBytes a size (in bytes) that the total index summary space usage should stay close to or
* under, if possible
* @return a list of new SSTableReader instances
*/
@VisibleForTesting
public static List redistributeSummaries(List compacting, List nonCompacting, long memoryPoolBytes) throws IOException
{
long total = 0;
for (SSTableReader sstable : Iterables.concat(compacting, nonCompacting))
total += sstable.getIndexSummaryOffHeapSize();
logger.debug("Beginning redistribution of index summaries for {} sstables with memory pool size {} MB; current spaced used is {} MB",
nonCompacting.size(), memoryPoolBytes / 1024L / 1024L, total / 1024.0 / 1024.0);
final Map readRates = new HashMap<>(nonCompacting.size());
double totalReadsPerSec = 0.0;
for (SSTableReader sstable : nonCompacting)
{
if (sstable.readMeter != null)
{
Double readRate = sstable.readMeter.fifteenMinuteRate();
totalReadsPerSec += readRate;
readRates.put(sstable, readRate);
}
}
logger.trace("Total reads/sec across all sstables in index summary resize process: {}", totalReadsPerSec);
// copy and sort by read rates (ascending)
List sstablesByHotness = new ArrayList<>(nonCompacting);
Collections.sort(sstablesByHotness, new ReadRateComparator(readRates));
long remainingBytes = memoryPoolBytes;
for (SSTableReader sstable : compacting)
remainingBytes -= sstable.getIndexSummaryOffHeapSize();
logger.trace("Index summaries for compacting SSTables are using {} MB of space",
(memoryPoolBytes - remainingBytes) / 1024.0 / 1024.0);
List newSSTables = adjustSamplingLevels(sstablesByHotness, totalReadsPerSec, remainingBytes);
total = 0;
for (SSTableReader sstable : Iterables.concat(compacting, newSSTables))
total += sstable.getIndexSummaryOffHeapSize();
logger.debug("Completed resizing of index summaries; current approximate memory used: {} MB",
total / 1024.0 / 1024.0);
return newSSTables;
}
private static List adjustSamplingLevels(List sstables,
double totalReadsPerSec, long memoryPoolCapacity) throws IOException
{
List toDownsample = new ArrayList<>(sstables.size() / 4);
List toUpsample = new ArrayList<>(sstables.size() / 4);
List forceResample = new ArrayList<>();
List forceUpsample = new ArrayList<>();
List newSSTables = new ArrayList<>(sstables.size());
// Going from the coldest to the hottest sstables, try to give each sstable an amount of space proportional
// to the number of total reads/sec it handles.
long remainingSpace = memoryPoolCapacity;
for (SSTableReader sstable : sstables)
{
int minIndexInterval = sstable.metadata.getMinIndexInterval();
int maxIndexInterval = sstable.metadata.getMaxIndexInterval();
double readsPerSec = sstable.readMeter == null ? 0.0 : sstable.readMeter.fifteenMinuteRate();
long idealSpace = Math.round(remainingSpace * (readsPerSec / totalReadsPerSec));
// figure out how many entries our idealSpace would buy us, and pick a new sampling level based on that
int currentNumEntries = sstable.getIndexSummarySize();
double avgEntrySize = sstable.getIndexSummaryOffHeapSize() / (double) currentNumEntries;
long targetNumEntries = Math.max(1, Math.round(idealSpace / avgEntrySize));
int currentSamplingLevel = sstable.getIndexSummarySamplingLevel();
int maxSummarySize = sstable.getMaxIndexSummarySize();
// if the min_index_interval changed, calculate what our current sampling level would be under the new min
if (sstable.getMinIndexInterval() != minIndexInterval)
{
int effectiveSamplingLevel = (int) Math.round(currentSamplingLevel * (minIndexInterval / (double) sstable.getMinIndexInterval()));
maxSummarySize = (int) Math.round(maxSummarySize * (sstable.getMinIndexInterval() / (double) minIndexInterval));
logger.trace("min_index_interval changed from {} to {}, so the current sampling level for {} is effectively now {} (was {})",
sstable.getMinIndexInterval(), minIndexInterval, sstable, effectiveSamplingLevel, currentSamplingLevel);
currentSamplingLevel = effectiveSamplingLevel;
}
int newSamplingLevel = IndexSummaryBuilder.calculateSamplingLevel(currentSamplingLevel, currentNumEntries, targetNumEntries,
minIndexInterval, maxIndexInterval);
int numEntriesAtNewSamplingLevel = IndexSummaryBuilder.entriesAtSamplingLevel(newSamplingLevel, maxSummarySize);
double effectiveIndexInterval = sstable.getEffectiveIndexInterval();
logger.trace("{} has {} reads/sec; ideal space for index summary: {} bytes ({} entries); considering moving " +
"from level {} ({} entries, {} bytes) to level {} ({} entries, {} bytes)",
sstable.getFilename(), readsPerSec, idealSpace, targetNumEntries, currentSamplingLevel, currentNumEntries,
currentNumEntries * avgEntrySize, newSamplingLevel, numEntriesAtNewSamplingLevel,
numEntriesAtNewSamplingLevel * avgEntrySize);
if (effectiveIndexInterval < minIndexInterval)
{
// The min_index_interval was changed; re-sample to match it.
logger.debug("Forcing resample of {} because the current index interval ({}) is below min_index_interval ({})",
sstable, effectiveIndexInterval, minIndexInterval);
long spaceUsed = (long) Math.ceil(avgEntrySize * numEntriesAtNewSamplingLevel);
forceResample.add(new ResampleEntry(sstable, spaceUsed, newSamplingLevel));
remainingSpace -= spaceUsed;
}
else if (effectiveIndexInterval > maxIndexInterval)
{
// The max_index_interval was lowered; force an upsample to the effective minimum sampling level
logger.debug("Forcing upsample of {} because the current index interval ({}) is above max_index_interval ({})",
sstable, effectiveIndexInterval, maxIndexInterval);
newSamplingLevel = Math.max(1, (BASE_SAMPLING_LEVEL * minIndexInterval) / maxIndexInterval);
numEntriesAtNewSamplingLevel = IndexSummaryBuilder.entriesAtSamplingLevel(newSamplingLevel, sstable.getMaxIndexSummarySize());
long spaceUsed = (long) Math.ceil(avgEntrySize * numEntriesAtNewSamplingLevel);
forceUpsample.add(new ResampleEntry(sstable, spaceUsed, newSamplingLevel));
remainingSpace -= avgEntrySize * numEntriesAtNewSamplingLevel;
}
else if (targetNumEntries >= currentNumEntries * UPSAMPLE_THRESHOLD && newSamplingLevel > currentSamplingLevel)
{
long spaceUsed = (long) Math.ceil(avgEntrySize * numEntriesAtNewSamplingLevel);
toUpsample.add(new ResampleEntry(sstable, spaceUsed, newSamplingLevel));
remainingSpace -= avgEntrySize * numEntriesAtNewSamplingLevel;
}
else if (targetNumEntries < currentNumEntries * DOWNSAMPLE_THESHOLD && newSamplingLevel < currentSamplingLevel)
{
long spaceUsed = (long) Math.ceil(avgEntrySize * numEntriesAtNewSamplingLevel);
toDownsample.add(new ResampleEntry(sstable, spaceUsed, newSamplingLevel));
remainingSpace -= spaceUsed;
}
else
{
// keep the same sampling level
logger.trace("SSTable {} is within thresholds of ideal sampling", sstable);
remainingSpace -= sstable.getIndexSummaryOffHeapSize();
newSSTables.add(sstable);
}
totalReadsPerSec -= readsPerSec;
}
if (remainingSpace > 0)
{
Pair, List> result = distributeRemainingSpace(toDownsample, remainingSpace);
toDownsample = result.right;
newSSTables.addAll(result.left);
}
// downsample first, then upsample
toDownsample.addAll(forceResample);
toDownsample.addAll(toUpsample);
toDownsample.addAll(forceUpsample);
Multimap replacedByTracker = HashMultimap.create();
Multimap replacementsByTracker = HashMultimap.create();
for (ResampleEntry entry : toDownsample)
{
SSTableReader sstable = entry.sstable;
logger.debug("Re-sampling index summary for {} from {}/{} to {}/{} of the original number of entries",
sstable, sstable.getIndexSummarySamplingLevel(), Downsampling.BASE_SAMPLING_LEVEL,
entry.newSamplingLevel, Downsampling.BASE_SAMPLING_LEVEL);
ColumnFamilyStore cfs = Keyspace.open(sstable.getKeyspaceName()).getColumnFamilyStore(sstable.getColumnFamilyName());
SSTableReader replacement = sstable.cloneWithNewSummarySamplingLevel(cfs, entry.newSamplingLevel);
DataTracker tracker = cfs.getDataTracker();
replacedByTracker.put(tracker, sstable);
replacementsByTracker.put(tracker, replacement);
}
for (DataTracker tracker : replacedByTracker.keySet())
{
tracker.replaceWithNewInstances(replacedByTracker.get(tracker), replacementsByTracker.get(tracker));
newSSTables.addAll(replacementsByTracker.get(tracker));
}
return newSSTables;
}
@VisibleForTesting
static Pair, List> distributeRemainingSpace(List toDownsample, long remainingSpace)
{
// sort by the amount of space regained by doing the downsample operation; we want to try to avoid operations
// that will make little difference.
Collections.sort(toDownsample, new Comparator()
{
public int compare(ResampleEntry o1, ResampleEntry o2)
{
return Double.compare(o1.sstable.getIndexSummaryOffHeapSize() - o1.newSpaceUsed,
o2.sstable.getIndexSummaryOffHeapSize() - o2.newSpaceUsed);
}
});
int noDownsampleCutoff = 0;
List willNotDownsample = new ArrayList<>();
while (remainingSpace > 0 && noDownsampleCutoff < toDownsample.size())
{
ResampleEntry entry = toDownsample.get(noDownsampleCutoff);
long extraSpaceRequired = entry.sstable.getIndexSummaryOffHeapSize() - entry.newSpaceUsed;
// see if we have enough leftover space to keep the current sampling level
if (extraSpaceRequired <= remainingSpace)
{
logger.trace("Using leftover space to keep {} at the current sampling level ({})",
entry.sstable, entry.sstable.getIndexSummarySamplingLevel());
willNotDownsample.add(entry.sstable);
remainingSpace -= extraSpaceRequired;
}
else
{
break;
}
noDownsampleCutoff++;
}
return Pair.create(willNotDownsample, toDownsample.subList(noDownsampleCutoff, toDownsample.size()));
}
private static class ResampleEntry
{
public final SSTableReader sstable;
public final long newSpaceUsed;
public final int newSamplingLevel;
public ResampleEntry(SSTableReader sstable, long newSpaceUsed, int newSamplingLevel)
{
this.sstable = sstable;
this.newSpaceUsed = newSpaceUsed;
this.newSamplingLevel = newSamplingLevel;
}
}
/** Utility class for sorting sstables by their read rates. */
private static class ReadRateComparator implements Comparator
{
private final Map readRates;
public ReadRateComparator(Map readRates)
{
this.readRates = readRates;
}
@Override
public int compare(SSTableReader o1, SSTableReader o2)
{
Double readRate1 = readRates.get(o1);
Double readRate2 = readRates.get(o2);
if (readRate1 == null && readRate2 == null)
return 0;
else if (readRate1 == null)
return -1;
else if (readRate2 == null)
return 1;
else
return Double.compare(readRate1, readRate2);
}
}
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