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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;
import java.io.File;
import java.util.AbstractMap;
import java.util.Iterator;
import java.util.Map;
import java.util.concurrent.ConcurrentNavigableMap;
import java.util.concurrent.ConcurrentSkipListMap;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;
import com.google.common.annotations.VisibleForTesting;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.cassandra.config.CFMetaData;
import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.db.commitlog.CommitLog;
import org.apache.cassandra.db.commitlog.ReplayPosition;
import org.apache.cassandra.db.composites.CellNameType;
import org.apache.cassandra.db.index.SecondaryIndexManager;
import org.apache.cassandra.dht.Murmur3Partitioner.LongToken;
import org.apache.cassandra.io.sstable.Descriptor;
import org.apache.cassandra.io.sstable.format.SSTableReader;
import org.apache.cassandra.io.sstable.format.SSTableWriter;
import org.apache.cassandra.io.sstable.metadata.MetadataCollector;
import org.apache.cassandra.service.ActiveRepairService;
import org.apache.cassandra.utils.*;
import org.apache.cassandra.utils.concurrent.OpOrder;
import org.apache.cassandra.utils.memory.*;
public class Memtable implements Comparable
{
private static final Logger logger = LoggerFactory.getLogger(Memtable.class);
static final MemtablePool MEMORY_POOL = DatabaseDescriptor.getMemtableAllocatorPool();
private static final int ROW_OVERHEAD_HEAP_SIZE = estimateRowOverhead(Integer.parseInt(System.getProperty("cassandra.memtable_row_overhead_computation_step", "100000")));
private final MemtableAllocator allocator;
private final AtomicLong liveDataSize = new AtomicLong(0);
private final AtomicLong currentOperations = new AtomicLong(0);
// the write barrier for directing writes to this memtable during a switch
private volatile OpOrder.Barrier writeBarrier;
// the precise upper bound of ReplayPosition owned by this memtable
private volatile AtomicReference commitLogUpperBound;
// the precise lower bound of ReplayPosition owned by this memtable; equal to its predecessor's commitLogUpperBound
private AtomicReference commitLogLowerBound;
// the approximate lower bound by this memtable; must be <= commitLogLowerBound once our predecessor
// has been finalised, and this is enforced in the ColumnFamilyStore.setCommitLogUpperBound
private final ReplayPosition approximateCommitLogLowerBound = CommitLog.instance.getContext();
public int compareTo(Memtable that)
{
return this.approximateCommitLogLowerBound.compareTo(that.approximateCommitLogLowerBound);
}
public static final class LastReplayPosition extends ReplayPosition
{
public LastReplayPosition(ReplayPosition copy) {
super(copy.segment, copy.position);
}
}
// We index the memtable by RowPosition only for the purpose of being able
// to select key range using Token.KeyBound. However put() ensures that we
// actually only store DecoratedKey.
private final ConcurrentNavigableMap rows = new ConcurrentSkipListMap<>();
public final ColumnFamilyStore cfs;
private final long creationNano = System.nanoTime();
// The smallest timestamp for all partitions stored in this memtable
private long minTimestamp = Long.MAX_VALUE;
// Record the comparator of the CFS at the creation of the memtable. This
// is only used when a user update the CF comparator, to know if the
// memtable was created with the new or old comparator.
public final CellNameType initialComparator;
public Memtable(AtomicReference commitLogLowerBound, ColumnFamilyStore cfs)
{
this.cfs = cfs;
this.commitLogLowerBound = commitLogLowerBound;
this.allocator = MEMORY_POOL.newAllocator();
this.initialComparator = cfs.metadata.comparator;
this.cfs.scheduleFlush();
}
// ONLY to be used for testing, to create a mock Memtable
@VisibleForTesting
public Memtable(CFMetaData metadata)
{
this.initialComparator = metadata.comparator;
this.cfs = null;
this.allocator = null;
}
public MemtableAllocator getAllocator()
{
return allocator;
}
public long getLiveDataSize()
{
return liveDataSize.get();
}
public long getOperations()
{
return currentOperations.get();
}
@VisibleForTesting
public void setDiscarding(OpOrder.Barrier writeBarrier, AtomicReference lastReplayPosition)
{
assert this.writeBarrier == null;
this.commitLogUpperBound = lastReplayPosition;
this.writeBarrier = writeBarrier;
allocator.setDiscarding();
}
void setDiscarded()
{
allocator.setDiscarded();
}
// decide if this memtable should take the write, or if it should go to the next memtable
public boolean accepts(OpOrder.Group opGroup, ReplayPosition replayPosition)
{
// if the barrier hasn't been set yet, then this memtable is still taking ALL writes
OpOrder.Barrier barrier = this.writeBarrier;
if (barrier == null)
return true;
// if the barrier has been set, but is in the past, we are definitely destined for a future memtable
if (!barrier.isAfter(opGroup))
return false;
// if we aren't durable we are directed only by the barrier
if (replayPosition == null)
return true;
while (true)
{
// otherwise we check if we are in the past/future wrt the CL boundary;
// if the boundary hasn't been finalised yet, we simply update it to the max of
// its current value and ours; if it HAS been finalised, we simply accept its judgement
// this permits us to coordinate a safe boundary, as the boundary choice is made
// atomically wrt our max() maintenance, so an operation cannot sneak into the past
ReplayPosition currentLast = commitLogUpperBound.get();
if (currentLast instanceof LastReplayPosition)
return currentLast.compareTo(replayPosition) >= 0;
if (currentLast != null && currentLast.compareTo(replayPosition) >= 0)
return true;
if (commitLogUpperBound.compareAndSet(currentLast, replayPosition))
return true;
}
}
public ReplayPosition getCommitLogLowerBound()
{
return commitLogLowerBound.get();
}
public boolean isLive()
{
return allocator.isLive();
}
public boolean isClean()
{
return rows.isEmpty();
}
public boolean mayContainDataBefore(ReplayPosition position)
{
return approximateCommitLogLowerBound.compareTo(position) < 0;
}
/**
* @return true if this memtable is expired. Expiration time is determined by CF's memtable_flush_period_in_ms.
*/
public boolean isExpired()
{
int period = cfs.metadata.getMemtableFlushPeriod();
return period > 0 && (System.nanoTime() - creationNano >= TimeUnit.MILLISECONDS.toNanos(period));
}
/**
* Should only be called by ColumnFamilyStore.apply via Keyspace.apply, which supplies the appropriate
* OpOrdering.
*
* replayPosition should only be null if this is a secondary index, in which case it is *expected* to be null
*/
long put(DecoratedKey key, ColumnFamily cf, SecondaryIndexManager.Updater indexer, OpOrder.Group opGroup)
{
AtomicBTreeColumns previous = rows.get(key);
long initialSize = 0;
if (previous == null)
{
AtomicBTreeColumns empty = cf.cloneMeShallow(AtomicBTreeColumns.factory, false);
final DecoratedKey cloneKey = allocator.clone(key, opGroup);
// We'll add the columns later. This avoids wasting works if we get beaten in the putIfAbsent
previous = rows.putIfAbsent(cloneKey, empty);
if (previous == null)
{
previous = empty;
// allocate the row overhead after the fact; this saves over allocating and having to free after, but
// means we can overshoot our declared limit.
int overhead = (int) (key.getToken().getHeapSize() + ROW_OVERHEAD_HEAP_SIZE);
allocator.onHeap().allocate(overhead, opGroup);
initialSize = 8;
}
else
{
allocator.reclaimer().reclaimImmediately(cloneKey);
}
}
final AtomicBTreeColumns.ColumnUpdater updater = previous.addAllWithSizeDelta(cf, allocator, opGroup, indexer);
minTimestamp = Math.min(minTimestamp, updater.minTimestamp);
liveDataSize.addAndGet(initialSize + updater.dataSize);
currentOperations.addAndGet(cf.getColumnCount() + (cf.isMarkedForDelete() ? 1 : 0) + cf.deletionInfo().rangeCount());
return updater.colUpdateTimeDelta;
}
// for debugging
public String contents()
{
StringBuilder builder = new StringBuilder();
builder.append("{");
for (Map.Entry entry : rows.entrySet())
{
builder.append(entry.getKey()).append(": ").append(entry.getValue()).append(", ");
}
builder.append("}");
return builder.toString();
}
public int partitionCount()
{
return rows.size();
}
public String toString()
{
return String.format("Memtable-%s@%s(%s serialized bytes, %s ops, %.0f%%/%.0f%% of on/off-heap limit)",
cfs.name, hashCode(), FBUtilities.prettyPrintMemory(liveDataSize.get()), currentOperations,
100 * allocator.onHeap().ownershipRatio(), 100 * allocator.offHeap().ownershipRatio());
}
/**
* @param startWith Include data in the result from and including this key and to the end of the memtable
* @return An iterator of entries with the data from the start key
*/
public Iterator> getEntryIterator(final RowPosition startWith, final RowPosition stopAt)
{
return new Iterator>()
{
private Iterator> iter = stopAt.isMinimum()
? rows.tailMap(startWith).entrySet().iterator()
: rows.subMap(startWith, true, stopAt, true).entrySet().iterator();
private Map.Entry currentEntry;
public boolean hasNext()
{
return iter.hasNext();
}
public Map.Entry next()
{
Map.Entry entryRowPosition = iter.next();
// Actual stored key should be true DecoratedKey
assert entryRowPosition.getKey() instanceof DecoratedKey;
@SuppressWarnings("unchecked") // Object cast is required since otherwise we can't turn RowPosition into DecoratedKey
Map.Entry entry = (Map.Entry) entryRowPosition;
if (MEMORY_POOL.needToCopyOnHeap())
{
DecoratedKey key = entry.getKey();
key = new BufferDecoratedKey(key.getToken(), HeapAllocator.instance.clone(key.getKey()));
ColumnFamily cells = ArrayBackedSortedColumns.localCopy(entry.getValue(), HeapAllocator.instance);
entry = new AbstractMap.SimpleImmutableEntry<>(key, cells);
}
// Store the reference to the current entry so that remove() can update the current size.
currentEntry = entry;
return entry;
}
public void remove()
{
iter.remove();
liveDataSize.addAndGet(-currentEntry.getValue().dataSize());
currentEntry = null;
}
};
}
public ColumnFamily getColumnFamily(DecoratedKey key)
{
return rows.get(key);
}
public SSTableReader flush()
{
long estimatedSize = estimatedSize();
Directories.DataDirectory dataDirectory = cfs.directories.getWriteableLocation(estimatedSize);
File sstableDirectory = cfs.directories.getLocationForDisk(dataDirectory);
assert sstableDirectory != null : "Flush task is not bound to any disk";
return writeSortedContents(sstableDirectory);
}
public long getMinTimestamp()
{
return minTimestamp;
}
private long estimatedSize()
{
long keySize = 0;
for (RowPosition key : rows.keySet())
{
// make sure we don't write non-sensical keys
assert key instanceof DecoratedKey;
keySize += ((DecoratedKey)key).getKey().remaining();
}
return (long) ((keySize // index entries
+ keySize // keys in data file
+ liveDataSize.get()) // data
* 1.2); // bloom filter and row index overhead
}
private SSTableReader writeSortedContents(File sstableDirectory)
{
logger.info("Writing {}", Memtable.this.toString());
SSTableReader ssTable;
// errors when creating the writer that may leave empty temp files.
try (SSTableWriter writer = createFlushWriter(cfs.getTempSSTablePath(sstableDirectory)))
{
boolean trackContention = logger.isTraceEnabled();
int heavilyContendedRowCount = 0;
// (we can't clear out the map as-we-go to free up memory,
// since the memtable is being used for queries in the "pending flush" category)
for (Map.Entry entry : rows.entrySet())
{
AtomicBTreeColumns cf = entry.getValue();
if (cf.isMarkedForDelete() && cf.hasColumns())
{
// When every node is up, there's no reason to write batchlog data out to sstables
// (which in turn incurs cost like compaction) since the BL write + delete cancel each other out,
// and BL data is strictly local, so we don't need to preserve tombstones for repair.
// If we have a data row + row level tombstone, then writing it is effectively an expensive no-op so we skip it.
// See CASSANDRA-4667.
if (cfs.name.equals(SystemKeyspace.BATCHLOG) && cfs.keyspace.getName().equals(SystemKeyspace.NAME))
continue;
}
if (trackContention && cf.usePessimisticLocking())
heavilyContendedRowCount++;
if (!cf.isEmpty())
writer.append((DecoratedKey)entry.getKey(), cf);
}
if (writer.getFilePointer() > 0)
{
logger.debug(String.format("Completed flushing %s (%s) for commitlog position %s",
writer.getFilename(),
FBUtilities.prettyPrintMemory(writer.getOnDiskFilePointer()),
commitLogUpperBound));
// temp sstables should contain non-repaired data.
ssTable = writer.finish(true);
}
else
{
logger.debug("Completed flushing {}; nothing needed to be retained. Commitlog position was {}",
writer.getFilename(), commitLogUpperBound);
writer.abort();
ssTable = null;
}
if (heavilyContendedRowCount > 0)
logger.trace(String.format("High update contention in %d/%d partitions of %s ", heavilyContendedRowCount, rows.size(), Memtable.this.toString()));
return ssTable;
}
}
private SSTableWriter createFlushWriter(String filename)
{
MetadataCollector sstableMetadataCollector = new MetadataCollector(cfs.metadata.comparator)
.commitLogLowerBound(commitLogLowerBound.get())
.commitLogUpperBound(commitLogUpperBound.get());
return SSTableWriter.create(Descriptor.fromFilename(filename), (long) rows.size(), ActiveRepairService.UNREPAIRED_SSTABLE, cfs.metadata, cfs.partitioner, sstableMetadataCollector);
}
private static int estimateRowOverhead(final int count)
{
// calculate row overhead
try (final OpOrder.Group group = new OpOrder().start())
{
int rowOverhead;
MemtableAllocator allocator = MEMORY_POOL.newAllocator();
ConcurrentNavigableMap rows = new ConcurrentSkipListMap<>();
final Object val = new Object();
for (int i = 0; i < count; i++)
rows.put(allocator.clone(new BufferDecoratedKey(new LongToken(i), ByteBufferUtil.EMPTY_BYTE_BUFFER), group), val);
double avgSize = ObjectSizes.measureDeep(rows) / (double) count;
rowOverhead = (int) ((avgSize - Math.floor(avgSize)) < 0.05 ? Math.floor(avgSize) : Math.ceil(avgSize));
rowOverhead -= ObjectSizes.measureDeep(new LongToken(0));
rowOverhead += AtomicBTreeColumns.EMPTY_SIZE;
allocator.setDiscarding();
allocator.setDiscarded();
return rowOverhead;
}
}
}