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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.
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package org.apache.cassandra.db.memtable;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NavigableSet;
import java.util.Objects;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.ReentrantLock;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.Iterators;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.db.BufferDecoratedKey;
import org.apache.cassandra.db.Clustering;
import org.apache.cassandra.db.ColumnFamilyStore;
import org.apache.cassandra.db.DataRange;
import org.apache.cassandra.db.DecoratedKey;
import org.apache.cassandra.db.DeletionInfo;
import org.apache.cassandra.db.PartitionPosition;
import org.apache.cassandra.db.RegularAndStaticColumns;
import org.apache.cassandra.db.Slices;
import org.apache.cassandra.db.commitlog.CommitLogPosition;
import org.apache.cassandra.db.filter.ClusteringIndexFilter;
import org.apache.cassandra.db.filter.ColumnFilter;
import org.apache.cassandra.db.partitions.AbstractUnfilteredPartitionIterator;
import org.apache.cassandra.db.partitions.BTreePartitionData;
import org.apache.cassandra.db.partitions.BTreePartitionUpdater;
import org.apache.cassandra.db.partitions.ImmutableBTreePartition;
import org.apache.cassandra.db.partitions.Partition;
import org.apache.cassandra.db.partitions.PartitionUpdate;
import org.apache.cassandra.db.partitions.UnfilteredPartitionIterator;
import org.apache.cassandra.db.rows.EncodingStats;
import org.apache.cassandra.db.rows.Row;
import org.apache.cassandra.db.rows.UnfilteredRowIterator;
import org.apache.cassandra.db.tries.InMemoryTrie;
import org.apache.cassandra.db.tries.Trie;
import org.apache.cassandra.dht.AbstractBounds;
import org.apache.cassandra.dht.Bounds;
import org.apache.cassandra.dht.IncludingExcludingBounds;
import org.apache.cassandra.dht.Range;
import org.apache.cassandra.index.transactions.UpdateTransaction;
import org.apache.cassandra.io.compress.BufferType;
import org.apache.cassandra.io.sstable.SSTableReadsListener;
import org.apache.cassandra.metrics.TableMetrics;
import org.apache.cassandra.metrics.TrieMemtableMetricsView;
import org.apache.cassandra.schema.TableMetadata;
import org.apache.cassandra.schema.TableMetadataRef;
import org.apache.cassandra.utils.Clock;
import org.apache.cassandra.utils.bytecomparable.ByteComparable;
import org.apache.cassandra.utils.bytecomparable.ByteSource;
import org.apache.cassandra.utils.concurrent.OpOrder;
import org.apache.cassandra.utils.memory.EnsureOnHeap;
import org.apache.cassandra.utils.memory.MemtableAllocator;
import org.github.jamm.Unmetered;
/**
* Trie memtable implementation. Improves memory usage, garbage collection efficiency and lookup performance.
* The implementation is described in detail in the paper:
* https://www.vldb.org/pvldb/vol15/p3359-lambov.pdf
*
* The configuration takes a single parameter:
* - shards: the number of shards to split into, defaulting to the number of CPU cores.
*
* Also see Memtable_API.md.
*/
public class TrieMemtable extends AbstractShardedMemtable
{
private static final Logger logger = LoggerFactory.getLogger(TrieMemtable.class);
/** Buffer type to use for memtable tries (on- vs off-heap) */
public static final BufferType BUFFER_TYPE;
static
{
switch (DatabaseDescriptor.getMemtableAllocationType())
{
case unslabbed_heap_buffers:
case heap_buffers:
BUFFER_TYPE = BufferType.ON_HEAP;
break;
case offheap_buffers:
case offheap_objects:
BUFFER_TYPE = BufferType.OFF_HEAP;
break;
default:
throw new AssertionError();
}
}
/** If keys is below this length, we will use a recursive procedure for inserting data in the memtable trie. */
@VisibleForTesting
public static final int MAX_RECURSIVE_KEY_LENGTH = 128;
/** The byte-ordering conversion version to use for memtables. */
public static final ByteComparable.Version BYTE_COMPARABLE_VERSION = ByteComparable.Version.OSS50;
// Set to true when the memtable requests a switch (e.g. for trie size limit being reached) to ensure only one
// thread calls cfs.switchMemtableIfCurrent.
private final AtomicBoolean switchRequested = new AtomicBoolean(false);
/**
* Sharded memtable sections. Each is responsible for a contiguous range of the token space (between boundaries[i]
* and boundaries[i+1]) and is written to by one thread at a time, while reads are carried out concurrently
* (including with any write).
*/
private final MemtableShard[] shards;
/**
* A merged view of the memtable map. Used for partition range queries and flush.
* For efficiency we serve single partition requests off the shard which offers more direct InMemoryTrie methods.
*/
private final Trie mergedTrie;
@Unmetered
private final TrieMemtableMetricsView metrics;
TrieMemtable(AtomicReference commitLogLowerBound, TableMetadataRef metadataRef, Owner owner, Integer shardCountOption)
{
super(commitLogLowerBound, metadataRef, owner, shardCountOption);
this.metrics = new TrieMemtableMetricsView(metadataRef.keyspace, metadataRef.name);
this.shards = generatePartitionShards(boundaries.shardCount(), allocator, metadataRef, metrics);
this.mergedTrie = makeMergedTrie(shards);
}
private static MemtableShard[] generatePartitionShards(int splits,
MemtableAllocator allocator,
TableMetadataRef metadata,
TrieMemtableMetricsView metrics)
{
MemtableShard[] partitionMapContainer = new MemtableShard[splits];
for (int i = 0; i < splits; i++)
partitionMapContainer[i] = new MemtableShard(metadata, allocator, metrics);
return partitionMapContainer;
}
private static Trie makeMergedTrie(MemtableShard[] shards)
{
List> tries = new ArrayList<>(shards.length);
for (MemtableShard shard : shards)
tries.add(shard.data);
return Trie.mergeDistinct(tries);
}
@Override
public boolean isClean()
{
for (MemtableShard shard : shards)
if (!shard.isClean())
return false;
return true;
}
@Override
public void discard()
{
super.discard();
// metrics here are not thread safe, but I think we can live with that
metrics.lastFlushShardDataSizes.reset();
for (MemtableShard shard : shards)
{
metrics.lastFlushShardDataSizes.update(shard.liveDataSize());
}
// the buffer release is a longer-running process, do it in a separate loop to not make the metrics update wait
for (MemtableShard shard : shards)
{
shard.data.discardBuffers();
}
}
/**
* Should only be called by ColumnFamilyStore.apply via Keyspace.apply, which supplies the appropriate
* OpOrdering.
*
* commitLogSegmentPosition should only be null if this is a secondary index, in which case it is *expected* to be null
*/
@Override
public long put(PartitionUpdate update, UpdateTransaction indexer, OpOrder.Group opGroup)
{
try
{
DecoratedKey key = update.partitionKey();
MemtableShard shard = shards[boundaries.getShardForKey(key)];
long colUpdateTimeDelta = shard.put(key, update, indexer, opGroup);
if (shard.data.reachedAllocatedSizeThreshold() && !switchRequested.getAndSet(true))
{
logger.info("Scheduling flush due to trie size limit reached.");
owner.signalFlushRequired(this, ColumnFamilyStore.FlushReason.MEMTABLE_LIMIT);
}
return colUpdateTimeDelta;
}
catch (InMemoryTrie.SpaceExhaustedException e)
{
// This should never happen as {@link InMemoryTrie#reachedAllocatedSizeThreshold} should become
// true and trigger a memtable switch long before this limit is reached.
throw new IllegalStateException(e);
}
}
/**
* Technically we should scatter gather on all the core threads because the size in following calls are not
* using volatile variables, but for metrics purpose this should be good enough.
*/
@Override
public long getLiveDataSize()
{
long total = 0L;
for (MemtableShard shard : shards)
total += shard.liveDataSize();
return total;
}
@Override
public long operationCount()
{
long total = 0L;
for (MemtableShard shard : shards)
total += shard.currentOperations();
return total;
}
@Override
public long partitionCount()
{
int total = 0;
for (MemtableShard shard : shards)
total += shard.size();
return total;
}
/**
* Returns the minTS if one available, otherwise NO_MIN_TIMESTAMP.
*
* EncodingStats uses a synthetic epoch TS at 2015. We don't want to leak that (CASSANDRA-18118) so we return NO_MIN_TIMESTAMP instead.
*
* @return The minTS or NO_MIN_TIMESTAMP if none available
*/
@Override
public long getMinTimestamp()
{
long min = Long.MAX_VALUE;
for (MemtableShard shard : shards)
min = Long.min(min, shard.minTimestamp());
return min != EncodingStats.NO_STATS.minTimestamp ? min : NO_MIN_TIMESTAMP;
}
@Override
public long getMinLocalDeletionTime()
{
long min = Long.MAX_VALUE;
for (MemtableShard shard : shards)
min = Long.min(min, shard.minLocalDeletionTime());
return min;
}
@Override
RegularAndStaticColumns columns()
{
for (MemtableShard shard : shards)
columnsCollector.update(shard.columnsCollector);
return columnsCollector.get();
}
@Override
EncodingStats encodingStats()
{
for (MemtableShard shard : shards)
statsCollector.update(shard.statsCollector.get());
return statsCollector.get();
}
@Override
public MemtableUnfilteredPartitionIterator partitionIterator(final ColumnFilter columnFilter,
final DataRange dataRange,
SSTableReadsListener readsListener)
{
AbstractBounds keyRange = dataRange.keyRange();
PartitionPosition left = keyRange.left;
PartitionPosition right = keyRange.right;
if (left.isMinimum())
left = null;
if (right.isMinimum())
right = null;
boolean isBound = keyRange instanceof Bounds;
boolean includeStart = isBound || keyRange instanceof IncludingExcludingBounds;
boolean includeStop = isBound || keyRange instanceof Range;
Trie subMap = mergedTrie.subtrie(left, includeStart, right, includeStop);
return new MemtableUnfilteredPartitionIterator(metadata(),
allocator.ensureOnHeap(),
subMap,
columnFilter,
dataRange);
// readsListener is ignored as it only accepts sstable signals
}
private Partition getPartition(DecoratedKey key)
{
int shardIndex = boundaries.getShardForKey(key);
BTreePartitionData data = shards[shardIndex].data.get(key);
if (data != null)
return createPartition(metadata(), allocator.ensureOnHeap(), key, data);
else
return null;
}
@Override
public UnfilteredRowIterator rowIterator(DecoratedKey key, Slices slices, ColumnFilter selectedColumns, boolean reversed, SSTableReadsListener listener)
{
Partition p = getPartition(key);
if (p == null)
return null;
else
return p.unfilteredIterator(selectedColumns, slices, reversed);
}
@Override
public UnfilteredRowIterator rowIterator(DecoratedKey key)
{
Partition p = getPartition(key);
return p != null ? p.unfilteredIterator() : null;
}
private static MemtablePartition createPartition(TableMetadata metadata, EnsureOnHeap ensureOnHeap, DecoratedKey key, BTreePartitionData data)
{
return new MemtablePartition(metadata, ensureOnHeap, key, data);
}
private static MemtablePartition getPartitionFromTrieEntry(TableMetadata metadata, EnsureOnHeap ensureOnHeap, Map.Entry en)
{
DecoratedKey key = BufferDecoratedKey.fromByteComparable(en.getKey(),
BYTE_COMPARABLE_VERSION,
metadata.partitioner);
return createPartition(metadata, ensureOnHeap, key, en.getValue());
}
@Override
public FlushablePartitionSet getFlushSet(PartitionPosition from, PartitionPosition to)
{
Trie toFlush = mergedTrie.subtrie(from, true, to, false);
long keySize = 0;
int keyCount = 0;
for (Iterator> it = toFlush.entryIterator(); it.hasNext(); )
{
Map.Entry en = it.next();
byte[] keyBytes = DecoratedKey.keyFromByteSource(ByteSource.peekable(en.getKey().asComparableBytes(BYTE_COMPARABLE_VERSION)),
BYTE_COMPARABLE_VERSION,
metadata().partitioner);
keySize += keyBytes.length;
keyCount++;
}
long partitionKeySize = keySize;
int partitionCount = keyCount;
return new AbstractFlushablePartitionSet()
{
public Memtable memtable()
{
return TrieMemtable.this;
}
public PartitionPosition from()
{
return from;
}
public PartitionPosition to()
{
return to;
}
public long partitionCount()
{
return partitionCount;
}
public Iterator iterator()
{
return Iterators.transform(toFlush.entryIterator(),
// During flushing we are certain the memtable will remain at least until
// the flush completes. No copying to heap is necessary.
entry -> getPartitionFromTrieEntry(metadata(), EnsureOnHeap.NOOP, entry));
}
public long partitionKeysSize()
{
return partitionKeySize;
}
};
}
static class MemtableShard
{
// The following fields are volatile as we have to make sure that when we
// collect results from all sub-ranges, the thread accessing the value
// is guaranteed to see the changes to the values.
// The smallest timestamp for all partitions stored in this shard
private volatile long minTimestamp = Long.MAX_VALUE;
private volatile long minLocalDeletionTime = Long.MAX_VALUE;
private volatile long liveDataSize = 0;
private volatile long currentOperations = 0;
@Unmetered
private final ReentrantLock writeLock = new ReentrantLock();
// Content map for the given shard. This is implemented as a memtable trie which uses the prefix-free
// byte-comparable ByteSource representations of the keys to address the partitions.
//
// This map is used in a single-producer, multi-consumer fashion: only one thread will insert items but
// several threads may read from it and iterate over it. Iterators (especially partition range iterators)
// may operate for a long period of time and thus iterators should not throw ConcurrentModificationExceptions
// if the underlying map is modified during iteration, they should provide a weakly consistent view of the map
// instead.
//
// Also, this data is backed by memtable memory, when accessing it callers must specify if it can be accessed
// unsafely, meaning that the memtable will not be discarded as long as the data is used, or whether the data
// should be copied on heap for off-heap allocators.
@VisibleForTesting
final InMemoryTrie data;
private final ColumnsCollector columnsCollector;
private final StatsCollector statsCollector;
@Unmetered // total pool size should not be included in memtable's deep size
private final MemtableAllocator allocator;
@Unmetered
private final TrieMemtableMetricsView metrics;
@VisibleForTesting
MemtableShard(TableMetadataRef metadata, MemtableAllocator allocator, TrieMemtableMetricsView metrics)
{
this.data = new InMemoryTrie<>(BUFFER_TYPE);
this.columnsCollector = new AbstractMemtable.ColumnsCollector(metadata.get().regularAndStaticColumns());
this.statsCollector = new AbstractMemtable.StatsCollector();
this.allocator = allocator;
this.metrics = metrics;
}
public long put(DecoratedKey key, PartitionUpdate update, UpdateTransaction indexer, OpOrder.Group opGroup) throws InMemoryTrie.SpaceExhaustedException
{
BTreePartitionUpdater updater = new BTreePartitionUpdater(allocator, allocator.cloner(opGroup), opGroup, indexer);
boolean locked = writeLock.tryLock();
if (locked)
{
metrics.uncontendedPuts.inc();
}
else
{
metrics.contendedPuts.inc();
long lockStartTime = Clock.Global.nanoTime();
writeLock.lock();
metrics.contentionTime.addNano(Clock.Global.nanoTime() - lockStartTime);
}
try
{
try
{
long onHeap = data.sizeOnHeap();
long offHeap = data.sizeOffHeap();
// Use the fast recursive put if we know the key is small enough to not cause a stack overflow.
data.putSingleton(key,
update,
updater::mergePartitions,
key.getKeyLength() < MAX_RECURSIVE_KEY_LENGTH);
allocator.offHeap().adjust(data.sizeOffHeap() - offHeap, opGroup);
allocator.onHeap().adjust(data.sizeOnHeap() - onHeap, opGroup);
}
finally
{
minTimestamp = Math.min(minTimestamp, update.stats().minTimestamp);
minLocalDeletionTime = Math.min(minLocalDeletionTime, update.stats().minLocalDeletionTime);
liveDataSize += updater.dataSize;
currentOperations += update.operationCount();
columnsCollector.update(update.columns());
statsCollector.update(update.stats());
}
}
finally
{
writeLock.unlock();
}
return updater.colUpdateTimeDelta;
}
public boolean isClean()
{
return data.isEmpty();
}
public int size()
{
return data.valuesCount();
}
long minTimestamp()
{
return minTimestamp;
}
long liveDataSize()
{
return liveDataSize;
}
long currentOperations()
{
return currentOperations;
}
long minLocalDeletionTime()
{
return minLocalDeletionTime;
}
}
static class MemtableUnfilteredPartitionIterator extends AbstractUnfilteredPartitionIterator implements UnfilteredPartitionIterator
{
private final TableMetadata metadata;
private final EnsureOnHeap ensureOnHeap;
private final Iterator> iter;
private final ColumnFilter columnFilter;
private final DataRange dataRange;
public MemtableUnfilteredPartitionIterator(TableMetadata metadata,
EnsureOnHeap ensureOnHeap,
Trie source,
ColumnFilter columnFilter,
DataRange dataRange)
{
this.metadata = metadata;
this.ensureOnHeap = ensureOnHeap;
this.iter = source.entryIterator();
this.columnFilter = columnFilter;
this.dataRange = dataRange;
}
public TableMetadata metadata()
{
return metadata;
}
public boolean hasNext()
{
return iter.hasNext();
}
public UnfilteredRowIterator next()
{
Partition partition = getPartitionFromTrieEntry(metadata(), ensureOnHeap, iter.next());
DecoratedKey key = partition.partitionKey();
ClusteringIndexFilter filter = dataRange.clusteringIndexFilter(key);
return filter.getUnfilteredRowIterator(columnFilter, partition);
}
}
static class MemtablePartition extends ImmutableBTreePartition
{
private final EnsureOnHeap ensureOnHeap;
private MemtablePartition(TableMetadata table, EnsureOnHeap ensureOnHeap, DecoratedKey key, BTreePartitionData data)
{
super(table, key, data);
this.ensureOnHeap = ensureOnHeap;
}
@Override
protected boolean canHaveShadowedData()
{
// The BtreePartitionData we store in the memtable are build iteratively by BTreePartitionData.add(), which
// doesn't make sure there isn't shadowed data, so we'll need to eliminate any.
return true;
}
@Override
public DeletionInfo deletionInfo()
{
return ensureOnHeap.applyToDeletionInfo(super.deletionInfo());
}
@Override
public Row staticRow()
{
return ensureOnHeap.applyToStatic(super.staticRow());
}
@Override
public DecoratedKey partitionKey()
{
return ensureOnHeap.applyToPartitionKey(super.partitionKey());
}
@Override
public Row getRow(Clustering clustering)
{
return ensureOnHeap.applyToRow(super.getRow(clustering));
}
@Override
public Row lastRow()
{
return ensureOnHeap.applyToRow(super.lastRow());
}
@Override
public UnfilteredRowIterator unfilteredIterator(ColumnFilter selection, Slices slices, boolean reversed)
{
return unfilteredIterator(holder(), selection, slices, reversed);
}
@Override
public UnfilteredRowIterator unfilteredIterator(ColumnFilter selection, NavigableSet> clusteringsInQueryOrder, boolean reversed)
{
return ensureOnHeap.applyToPartition(super.unfilteredIterator(selection, clusteringsInQueryOrder, reversed));
}
@Override
public UnfilteredRowIterator unfilteredIterator()
{
return unfilteredIterator(ColumnFilter.selection(super.columns()), Slices.ALL, false);
}
@Override
public UnfilteredRowIterator unfilteredIterator(BTreePartitionData current, ColumnFilter selection, Slices slices, boolean reversed)
{
return ensureOnHeap.applyToPartition(super.unfilteredIterator(current, selection, slices, reversed));
}
@Override
public Iterator iterator()
{
return ensureOnHeap.applyToPartition(super.iterator());
}
}
public static Factory factory(Map optionsCopy)
{
String shardsString = optionsCopy.remove(SHARDS_OPTION);
Integer shardCount = shardsString != null ? Integer.parseInt(shardsString) : null;
return new Factory(shardCount);
}
static class Factory implements Memtable.Factory
{
final Integer shardCount;
Factory(Integer shardCount)
{
this.shardCount = shardCount;
}
public Memtable create(AtomicReference commitLogLowerBound,
TableMetadataRef metadaRef,
Owner owner)
{
return new TrieMemtable(commitLogLowerBound, metadaRef, owner, shardCount);
}
@Override
public TableMetrics.ReleasableMetric createMemtableMetrics(TableMetadataRef metadataRef)
{
TrieMemtableMetricsView metrics = new TrieMemtableMetricsView(metadataRef.keyspace, metadataRef.name);
return metrics::release;
}
public boolean equals(Object o)
{
if (this == o)
return true;
if (o == null || getClass() != o.getClass())
return false;
Factory factory = (Factory) o;
return Objects.equals(shardCount, factory.shardCount);
}
public int hashCode()
{
return Objects.hash(shardCount);
}
}
@VisibleForTesting
public long unusedReservedMemory()
{
long size = 0;
for (MemtableShard shard : shards)
size += shard.data.unusedReservedMemory();
return size;
}
}
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