/*
* 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.commitlog;
import java.io.File;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.StandardOpenOption;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.zip.CRC32;
import com.codahale.metrics.Timer;
import org.cliffc.high_scale_lib.NonBlockingHashMap;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.cassandra.config.CFMetaData;
import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.config.Schema;
import org.apache.cassandra.db.Mutation;
import org.apache.cassandra.db.partitions.PartitionUpdate;
import org.apache.cassandra.io.FSWriteError;
import org.apache.cassandra.io.util.FileUtils;
import org.apache.cassandra.utils.CLibrary;
import org.apache.cassandra.utils.IntegerInterval;
import org.apache.cassandra.utils.concurrent.OpOrder;
import org.apache.cassandra.utils.concurrent.WaitQueue;
import static org.apache.cassandra.utils.FBUtilities.updateChecksumInt;
/*
* A single commit log file on disk. Manages creation of the file and writing mutations to disk,
* as well as tracking the last mutation position of any "dirty" CFs covered by the segment file. Segment
* files are initially allocated to a fixed size and can grow to accomidate a larger value if necessary.
*/
public abstract class CommitLogSegment
{
private static final Logger logger = LoggerFactory.getLogger(CommitLogSegment.class);
private final static long idBase;
private final static AtomicInteger nextId = new AtomicInteger(1);
private static long replayLimitId;
static
{
long maxId = Long.MIN_VALUE;
for (File file : new File(DatabaseDescriptor.getCommitLogLocation()).listFiles())
{
if (CommitLogDescriptor.isValid(file.getName()))
maxId = Math.max(CommitLogDescriptor.fromFileName(file.getName()).id, maxId);
}
replayLimitId = idBase = Math.max(System.currentTimeMillis(), maxId + 1);
}
// The commit log entry overhead in bytes (int: length + int: head checksum + int: tail checksum)
public static final int ENTRY_OVERHEAD_SIZE = 4 + 4 + 4;
// The commit log (chained) sync marker/header size in bytes (int: length + int: checksum [segmentId, position])
static final int SYNC_MARKER_SIZE = 4 + 4;
// The OpOrder used to order appends wrt sync
private final OpOrder appendOrder = new OpOrder();
private final AtomicInteger allocatePosition = new AtomicInteger();
// Everything before this offset has been synced and written. The SYNC_MARKER_SIZE bytes after
// each sync are reserved, and point forwards to the next such offset. The final
// sync marker in a segment will be zeroed out, or point to a position too close to the EOF to fit a marker.
private volatile int lastSyncedOffset;
// The end position of the buffer. Initially set to its capacity and updated to point to the last written position
// as the segment is being closed.
// No need to be volatile as writes are protected by appendOrder barrier.
private int endOfBuffer;
// a signal for writers to wait on to confirm the log message they provided has been written to disk
private final WaitQueue syncComplete = new WaitQueue();
// a map of Cf->dirty interval in this segment; if interval is not covered by the clean set, the log contains unflushed data
private final NonBlockingHashMap<UUID, IntegerInterval> cfDirty = new NonBlockingHashMap<>(1024);
// a map of Cf->clean intervals; separate map from above to permit marking Cfs clean whilst the log is still in use
private final ConcurrentHashMap<UUID, IntegerInterval.Set> cfClean = new ConcurrentHashMap<>();
public final long id;
final File logFile;
final FileChannel channel;
final int fd;
ByteBuffer buffer;
final CommitLog commitLog;
public final CommitLogDescriptor descriptor;
static CommitLogSegment createSegment(CommitLog commitLog, Runnable onClose)
{
return commitLog.configuration.useCompression() ? new CompressedSegment(commitLog, onClose)
: new MemoryMappedSegment(commitLog);
}
/**
* Checks if the segments use a buffer pool.
*
* @param commitLog the commit log
* @return <code>true</code> if the segments use a buffer pool, <code>false</code> otherwise.
*/
static boolean usesBufferPool(CommitLog commitLog)
{
return commitLog.configuration.useCompression();
}
static long getNextId()
{
return idBase + nextId.getAndIncrement();
}
/**
* Constructs a new segment file.
*
* @param filePath if not null, recycles the existing file by renaming it and truncating it to CommitLog.SEGMENT_SIZE.
*/
CommitLogSegment(CommitLog commitLog)
{
this.commitLog = commitLog;
id = getNextId();
descriptor = new CommitLogDescriptor(id, commitLog.configuration.getCompressorClass());
logFile = new File(commitLog.location, descriptor.fileName());
try
{
channel = FileChannel.open(logFile.toPath(), StandardOpenOption.WRITE, StandardOpenOption.READ, StandardOpenOption.CREATE);
fd = CLibrary.getfd(channel);
}
catch (IOException e)
{
throw new FSWriteError(e, logFile);
}
buffer = createBuffer(commitLog);
// write the header
CommitLogDescriptor.writeHeader(buffer, descriptor);
endOfBuffer = buffer.capacity();
lastSyncedOffset = buffer.position();
allocatePosition.set(lastSyncedOffset + SYNC_MARKER_SIZE);
}
abstract ByteBuffer createBuffer(CommitLog commitLog);
/**
* Allocate space in this buffer for the provided mutation, and return the allocated Allocation object.
* Returns null if there is not enough space in this segment, and a new segment is needed.
*/
@SuppressWarnings("resource") //we pass the op order around
Allocation allocate(Mutation mutation, int size)
{
final OpOrder.Group opGroup = appendOrder.start();
try
{
int position = allocate(size);
if (position < 0)
{
opGroup.close();
return null;
}
markDirty(mutation, position);
return new Allocation(this, opGroup, position, (ByteBuffer) buffer.duplicate().position(position).limit(position + size));
}
catch (Throwable t)
{
opGroup.close();
throw t;
}
}
static boolean shouldReplay(String name)
{
return CommitLogDescriptor.fromFileName(name).id < replayLimitId;
}
/**
* FOR TESTING PURPOSES.
*/
static void resetReplayLimit()
{
replayLimitId = getNextId();
}
// allocate bytes in the segment, or return -1 if not enough space
private int allocate(int size)
{
while (true)
{
int prev = allocatePosition.get();
int next = prev + size;
if (next >= endOfBuffer)
return -1;
if (allocatePosition.compareAndSet(prev, next))
{
assert buffer != null;
return prev;
}
}
}
// ensures no more of this segment is writeable, by allocating any unused section at the end and marking it discarded
void discardUnusedTail()
{
// We guard this with the OpOrdering instead of synchronised due to potential dead-lock with CLSM.advanceAllocatingFrom()
// Ensures endOfBuffer update is reflected in the buffer end position picked up by sync().
// This actually isn't strictly necessary, as currently all calls to discardUnusedTail are executed either by the thread
// running sync or within a mutation already protected by this OpOrdering, but to prevent future potential mistakes,
// we duplicate the protection here so that the contract between discardUnusedTail() and sync() is more explicit.
try (OpOrder.Group group = appendOrder.start())
{
while (true)
{
int prev = allocatePosition.get();
int next = endOfBuffer + 1;
if (prev >= next)
{
// Already stopped allocating, might also be closed.
assert buffer == null || prev == buffer.capacity() + 1;
return;
}
if (allocatePosition.compareAndSet(prev, next))
{
// Stopped allocating now. Can only succeed once, no further allocation or discardUnusedTail can succeed.
endOfBuffer = prev;
assert buffer != null && next == buffer.capacity() + 1;
return;
}
}
}
}
/**
* Wait for any appends or discardUnusedTail() operations started before this method was called
*/
void waitForModifications()
{
// issue a barrier and wait for it
appendOrder.awaitNewBarrier();
}
/**
* Forces a disk flush for this segment file.
*/
synchronized void sync()
{
boolean close = false;
// check we have more work to do
if (allocatePosition.get() <= lastSyncedOffset + SYNC_MARKER_SIZE)
return;
// Note: Even if the very first allocation of this sync section failed, we still want to enter this
// to ensure the segment is closed. As allocatePosition is set to 1 beyond the capacity of the buffer,
// this will always be entered when a mutation allocation has been attempted after the marker allocation
// succeeded in the previous sync.
assert buffer != null; // Only close once.
int startMarker = lastSyncedOffset;
// Allocate a new sync marker; this is both necessary in itself, but also serves to demarcate
// the point at which we can safely consider records to have been completely written to.
int nextMarker = allocate(SYNC_MARKER_SIZE);
if (nextMarker < 0)
{
// Ensure no more of this CLS is writeable, and mark ourselves for closing.
discardUnusedTail();
close = true;
// We use the buffer size as the synced position after a close instead of the end of the actual data
// to make sure we only close the buffer once.
// The endOfBuffer position may be incorrect at this point (to be written by another stalled thread).
nextMarker = buffer.capacity();
}
// Wait for mutations to complete as well as endOfBuffer to have been written.
waitForModifications();
int sectionEnd = close ? endOfBuffer : nextMarker;
// Perform compression, writing to file and flush.
write(startMarker, sectionEnd);
// Signal the sync as complete.
lastSyncedOffset = nextMarker;
if (close)
internalClose();
syncComplete.signalAll();
}
protected void writeSyncMarker(ByteBuffer buffer, int offset, int filePos, int nextMarker)
{
CRC32 crc = new CRC32();
updateChecksumInt(crc, (int) (id & 0xFFFFFFFFL));
updateChecksumInt(crc, (int) (id >>> 32));
updateChecksumInt(crc, filePos);
buffer.putInt(offset, nextMarker);
buffer.putInt(offset + 4, (int) crc.getValue());
}
abstract void write(int lastSyncedOffset, int nextMarker);
public boolean isStillAllocating()
{
return allocatePosition.get() < endOfBuffer;
}
/**
* Completely discards a segment file by deleting it. (Potentially blocking operation)
*/
void discard(boolean deleteFile)
{
close();
if (deleteFile)
FileUtils.deleteWithConfirm(logFile);
commitLog.allocator.addSize(-onDiskSize());
}
/**
* @return the current ReplayPosition for this log segment
*/
public ReplayPosition getContext()
{
return new ReplayPosition(id, allocatePosition.get());
}
/**
* @return the file path to this segment
*/
public String getPath()
{
return logFile.getPath();
}
/**
* @return the file name of this segment
*/
public String getName()
{
return logFile.getName();
}
void waitForFinalSync()
{
while (true)
{
WaitQueue.Signal signal = syncComplete.register();
if (lastSyncedOffset < endOfBuffer)
{
signal.awaitUninterruptibly();
}
else
{
signal.cancel();
break;
}
}
}
void waitForSync(int position, Timer waitingOnCommit)
{
while (lastSyncedOffset < position)
{
WaitQueue.Signal signal = waitingOnCommit != null ?
syncComplete.register(waitingOnCommit.time()) :
syncComplete.register();
if (lastSyncedOffset < position)
signal.awaitUninterruptibly();
else
signal.cancel();
}
}
/**
* Stop writing to this file, sync and close it. Does nothing if the file is already closed.
*/
synchronized void close()
{
discardUnusedTail();
sync();
assert buffer == null;
}
/**
* Close the segment file. Do not call from outside this class, use syncAndClose() instead.
*/
protected void internalClose()
{
try
{
channel.close();
buffer = null;
}
catch (IOException e)
{
throw new FSWriteError(e, getPath());
}
}
public static<K> void coverInMap(ConcurrentMap<K, IntegerInterval> map, K key, int value)
{
IntegerInterval i = map.get(key);
if (i == null)
{
i = map.putIfAbsent(key, new IntegerInterval(value, value));
if (i == null)
// success
return;
}
i.expandToCover(value);
}
void markDirty(Mutation mutation, int allocatedPosition)
{
for (PartitionUpdate update : mutation.getPartitionUpdates())
coverInMap(cfDirty, update.metadata().cfId, allocatedPosition);
}
/**
* Marks the ColumnFamily specified by cfId as clean for this log segment. If the
* given context argument is contained in this file, it will only mark the CF as
* clean if no newer writes have taken place.
*
* @param cfId the column family ID that is now clean
* @param context the optional clean offset
*/
public synchronized void markClean(UUID cfId, ReplayPosition startPosition, ReplayPosition endPosition)
{
if (startPosition.segment > id || endPosition.segment < id)
return;
if (!cfDirty.containsKey(cfId))
return;
int start = startPosition.segment == id ? startPosition.position : 0;
int end = endPosition.segment == id ? endPosition.position : Integer.MAX_VALUE;
cfClean.computeIfAbsent(cfId, k -> new IntegerInterval.Set()).add(start, end);
removeCleanFromDirty();
}
private void removeCleanFromDirty()
{
// if we're still allocating from this segment, don't touch anything since it can't be done thread-safely
if (isStillAllocating())
return;
Iterator<Map.Entry<UUID, IntegerInterval.Set>> iter = cfClean.entrySet().iterator();
while (iter.hasNext())
{
Map.Entry<UUID, IntegerInterval.Set> clean = iter.next();
UUID cfId = clean.getKey();
IntegerInterval.Set cleanSet = clean.getValue();
IntegerInterval dirtyInterval = cfDirty.get(cfId);
if (dirtyInterval != null && cleanSet.covers(dirtyInterval))
{
cfDirty.remove(cfId);
iter.remove();
}
}
}
/**
* @return a collection of dirty CFIDs for this segment file.
*/
public synchronized Collection<UUID> getDirtyCFIDs()
{
if (cfClean.isEmpty() || cfDirty.isEmpty())
return cfDirty.keySet();
List<UUID> r = new ArrayList<>(cfDirty.size());
for (Map.Entry<UUID, IntegerInterval> dirty : cfDirty.entrySet())
{
UUID cfId = dirty.getKey();
IntegerInterval dirtyInterval = dirty.getValue();
IntegerInterval.Set cleanSet = cfClean.get(cfId);
if (cleanSet == null || !cleanSet.covers(dirtyInterval))
r.add(dirty.getKey());
}
return r;
}
/**
* @return true if this segment is unused and safe to recycle or delete
*/
public synchronized boolean isUnused()
{
// if room to allocate, we're still in use as the active allocatingFrom,
// so we don't want to race with updates to cfClean with removeCleanFromDirty
if (isStillAllocating())
return false;
removeCleanFromDirty();
return cfDirty.isEmpty();
}
/**
* Check to see if a certain ReplayPosition is contained by this segment file.
*
* @param context the replay position to be checked
* @return true if the replay position is contained by this segment file.
*/
public boolean contains(ReplayPosition context)
{
return context.segment == id;
}
// For debugging, not fast
public String dirtyString()
{
StringBuilder sb = new StringBuilder();
for (UUID cfId : getDirtyCFIDs())
{
CFMetaData m = Schema.instance.getCFMetaData(cfId);
sb.append(m == null ? "<deleted>" : m.cfName).append(" (").append(cfId).append("), ");
}
return sb.toString();
}
abstract public long onDiskSize();
public long contentSize()
{
return lastSyncedOffset;
}
@Override
public String toString()
{
return "CommitLogSegment(" + getPath() + ')';
}
public static class CommitLogSegmentFileComparator implements Comparator<File>
{
public int compare(File f, File f2)
{
CommitLogDescriptor desc = CommitLogDescriptor.fromFileName(f.getName());
CommitLogDescriptor desc2 = CommitLogDescriptor.fromFileName(f2.getName());
return Long.compare(desc.id, desc2.id);
}
}
/**
* A simple class for tracking information about the portion of a segment that has been allocated to a log write.
* The constructor leaves the fields uninitialized for population by CommitlogManager, so that it can be
* stack-allocated by escape analysis in CommitLog.add.
*/
static class Allocation
{
private final CommitLogSegment segment;
private final OpOrder.Group appendOp;
private final int position;
private final ByteBuffer buffer;
Allocation(CommitLogSegment segment, OpOrder.Group appendOp, int position, ByteBuffer buffer)
{
this.segment = segment;
this.appendOp = appendOp;
this.position = position;
this.buffer = buffer;
}
CommitLogSegment getSegment()
{
return segment;
}
ByteBuffer getBuffer()
{
return buffer;
}
// markWritten() MUST be called once we are done with the segment or the CL will never flush
// but must not be called more than once
void markWritten()
{
appendOp.close();
}
void awaitDiskSync(Timer waitingOnCommit)
{
segment.waitForSync(position, waitingOnCommit);
}
public ReplayPosition getReplayPosition()
{
return new ReplayPosition(segment.id, buffer.limit());
}
}
}