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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.commitlog;
import java.io.File;
import java.io.IOException;
import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicLong;
import java.util.function.BooleanSupplier;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.util.concurrent.*;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import net.nicoulaj.compilecommand.annotations.DontInline;
import org.apache.cassandra.concurrent.NamedThreadFactory;
import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.io.compress.BufferType;
import org.apache.cassandra.io.util.FileUtils;
import org.apache.cassandra.io.util.SimpleCachedBufferPool;
import org.apache.cassandra.schema.Schema;
import org.apache.cassandra.db.*;
import org.apache.cassandra.schema.TableId;
import org.apache.cassandra.schema.TableMetadata;
import org.apache.cassandra.utils.*;
import org.apache.cassandra.utils.concurrent.WaitQueue;
import static org.apache.cassandra.db.commitlog.CommitLogSegment.Allocation;
/**
* Performs eager-creation of commit log segments in a background thread. All the
* public methods are thread safe.
*/
public abstract class AbstractCommitLogSegmentManager
{
static final Logger logger = LoggerFactory.getLogger(AbstractCommitLogSegmentManager.class);
/**
* Segment that is ready to be used. The management thread fills this and blocks until consumed.
*
* A single management thread produces this, and consumers are already synchronizing to make sure other work is
* performed atomically with consuming this. Volatile to make sure writes by the management thread become
* visible (ordered/lazySet would suffice). Consumers (advanceAllocatingFrom and discardAvailableSegment) must
* synchronize on 'this'.
*/
private volatile CommitLogSegment availableSegment = null;
private final WaitQueue segmentPrepared = new WaitQueue();
/** Active segments, containing unflushed data. The tail of this queue is the one we allocate writes to */
private final ConcurrentLinkedQueue activeSegments = new ConcurrentLinkedQueue<>();
/**
* The segment we are currently allocating commit log records to.
*
* Written by advanceAllocatingFrom which synchronizes on 'this'. Volatile to ensure reads get current value.
*/
private volatile CommitLogSegment allocatingFrom = null;
final String storageDirectory;
/**
* Tracks commitlog size, in multiples of the segment size. We need to do this so we can "promise" size
* adjustments ahead of actually adding/freeing segments on disk, so that the "evict oldest segment" logic
* can see the effect of recycling segments immediately (even though they're really happening asynchronously
* on the manager thread, which will take a ms or two).
*/
private final AtomicLong size = new AtomicLong();
@VisibleForTesting
Thread managerThread;
protected final CommitLog commitLog;
private volatile boolean shutdown;
private final BooleanSupplier managerThreadWaitCondition = () -> (availableSegment == null && !atSegmentBufferLimit()) || shutdown;
private final WaitQueue managerThreadWaitQueue = new WaitQueue();
private volatile SimpleCachedBufferPool bufferPool;
AbstractCommitLogSegmentManager(final CommitLog commitLog, String storageDirectory)
{
this.commitLog = commitLog;
this.storageDirectory = storageDirectory;
}
void start()
{
// The run loop for the manager thread
Runnable runnable = new WrappedRunnable()
{
public void runMayThrow() throws Exception
{
while (!shutdown)
{
try
{
assert availableSegment == null;
logger.trace("No segments in reserve; creating a fresh one");
availableSegment = createSegment();
if (shutdown)
{
// If shutdown() started and finished during segment creation, we are now left with a
// segment that no one will consume. Discard it.
discardAvailableSegment();
return;
}
segmentPrepared.signalAll();
Thread.yield();
if (availableSegment == null && !atSegmentBufferLimit())
// Writing threads need another segment now.
continue;
// Writing threads are not waiting for new segments, we can spend time on other tasks.
// flush old Cfs if we're full
maybeFlushToReclaim();
}
catch (Throwable t)
{
if (!CommitLog.handleCommitError("Failed managing commit log segments", t))
return;
// sleep some arbitrary period to avoid spamming CL
Uninterruptibles.sleepUninterruptibly(1, TimeUnit.SECONDS);
// If we offered a segment, wait for it to be taken before reentering the loop.
// There could be a new segment in next not offered, but only on failure to discard it while
// shutting down-- nothing more can or needs to be done in that case.
}
WaitQueue.waitOnCondition(managerThreadWaitCondition, managerThreadWaitQueue);
}
}
};
// For encrypted segments we want to keep the compression buffers on-heap as we need those bytes for encryption,
// and we want to avoid copying from off-heap (compression buffer) to on-heap encryption APIs
BufferType bufferType = commitLog.configuration.useEncryption() || !commitLog.configuration.useCompression()
? BufferType.ON_HEAP
: commitLog.configuration.getCompressor().preferredBufferType();
this.bufferPool = new SimpleCachedBufferPool(DatabaseDescriptor.getCommitLogMaxCompressionBuffersInPool(),
DatabaseDescriptor.getCommitLogSegmentSize(),
bufferType);
shutdown = false;
managerThread = NamedThreadFactory.createThread(runnable, "COMMIT-LOG-ALLOCATOR");
managerThread.start();
// for simplicity, ensure the first segment is allocated before continuing
advanceAllocatingFrom(null);
}
private boolean atSegmentBufferLimit()
{
return CommitLogSegment.usesBufferPool(commitLog) && bufferPool.atLimit();
}
private void maybeFlushToReclaim()
{
long unused = unusedCapacity();
if (unused < 0)
{
long flushingSize = 0;
List segmentsToRecycle = new ArrayList<>();
for (CommitLogSegment segment : activeSegments)
{
if (segment == allocatingFrom)
break;
flushingSize += segment.onDiskSize();
segmentsToRecycle.add(segment);
if (flushingSize + unused >= 0)
break;
}
flushDataFrom(segmentsToRecycle, false);
}
}
/**
* Allocate a segment within this CLSM. Should either succeed or throw.
*/
public abstract Allocation allocate(Mutation mutation, int size);
/**
* Hook to allow segment managers to track state surrounding creation of new segments. Onl perform as task submit
* to segment manager so it's performed on segment management thread.
*/
abstract CommitLogSegment createSegment();
/**
* Indicates that a segment file has been flushed and is no longer needed. Only perform as task submit to segment
* manager so it's performend on segment management thread, or perform while segment management thread is shutdown
* during testing resets.
*
* @param segment segment to be discarded
* @param delete whether or not the segment is safe to be deleted.
*/
abstract void discard(CommitLogSegment segment, boolean delete);
/**
* Advances the allocatingFrom pointer to the next prepared segment, but only if it is currently the segment provided.
*
* WARNING: Assumes segment management thread always succeeds in allocating a new segment or kills the JVM.
*/
@DontInline
void advanceAllocatingFrom(CommitLogSegment old)
{
while (true)
{
synchronized (this)
{
// do this in a critical section so we can maintain the order of segment construction when moving to allocatingFrom/activeSegments
if (allocatingFrom != old)
return;
// If a segment is ready, take it now, otherwise wait for the management thread to construct it.
if (availableSegment != null)
{
// Success! Change allocatingFrom and activeSegments (which must be kept in order) before leaving
// the critical section.
activeSegments.add(allocatingFrom = availableSegment);
availableSegment = null;
break;
}
}
awaitAvailableSegment(old);
}
// Signal the management thread to prepare a new segment.
wakeManager();
if (old != null)
{
// Now we can run the user defined command just after switching to the new commit log.
// (Do this here instead of in the recycle call so we can get a head start on the archive.)
commitLog.archiver.maybeArchive(old);
// ensure we don't continue to use the old file; not strictly necessary, but cleaner to enforce it
old.discardUnusedTail();
}
// request that the CL be synced out-of-band, as we've finished a segment
commitLog.requestExtraSync();
}
void awaitAvailableSegment(CommitLogSegment currentAllocatingFrom)
{
do
{
WaitQueue.Signal prepared = segmentPrepared.register(commitLog.metrics.waitingOnSegmentAllocation.time());
if (availableSegment == null && allocatingFrom == currentAllocatingFrom)
prepared.awaitUninterruptibly();
else
prepared.cancel();
}
while (availableSegment == null && allocatingFrom == currentAllocatingFrom);
}
/**
* Switch to a new segment, regardless of how much is left in the current one.
*
* Flushes any dirty CFs for this segment and any older segments, and then discards the segments.
* This is necessary to avoid resurrecting data during replay if a user creates a new table with
* the same name and ID. See CASSANDRA-16986 for more details.
*/
void forceRecycleAll(Iterable droppedTables)
{
List segmentsToRecycle = new ArrayList<>(activeSegments);
CommitLogSegment last = segmentsToRecycle.get(segmentsToRecycle.size() - 1);
advanceAllocatingFrom(last);
// wait for the commit log modifications
last.waitForModifications();
// make sure the writes have materialized inside of the memtables by waiting for all outstanding writes
// to complete
Keyspace.writeOrder.awaitNewBarrier();
// flush and wait for all CFs that are dirty in segments up-to and including 'last'
Future future = flushDataFrom(segmentsToRecycle, true);
try
{
future.get();
for (CommitLogSegment segment : activeSegments)
for (TableId tableId : droppedTables)
segment.markClean(tableId, CommitLogPosition.NONE, segment.getCurrentCommitLogPosition());
// now recycle segments that are unused, as we may not have triggered a discardCompletedSegments()
// if the previous active segment was the only one to recycle (since an active segment isn't
// necessarily dirty, and we only call dCS after a flush).
for (CommitLogSegment segment : activeSegments)
{
if (segment.isUnused())
archiveAndDiscard(segment);
}
CommitLogSegment first;
if ((first = activeSegments.peek()) != null && first.id <= last.id)
logger.error("Failed to force-recycle all segments; at least one segment is still in use with dirty CFs.");
}
catch (Throwable t)
{
// for now just log the error
logger.error("Failed waiting for a forced recycle of in-use commit log segments", t);
}
}
/**
* Indicates that a segment is no longer in use and that it should be discarded.
*
* @param segment segment that is no longer in use
*/
void archiveAndDiscard(final CommitLogSegment segment)
{
boolean archiveSuccess = commitLog.archiver.maybeWaitForArchiving(segment.getName());
if (!activeSegments.remove(segment))
return; // already discarded
// if archiving (command) was not successful then leave the file alone. don't delete or recycle.
logger.debug("Segment {} is no longer active and will be deleted {}", segment, archiveSuccess ? "now" : "by the archive script");
discard(segment, archiveSuccess);
}
/**
* Delete untracked segment files after replay
*
* @param file segment file that is no longer in use.
*/
void handleReplayedSegment(final File file)
{
// (don't decrease managed size, since this was never a "live" segment)
logger.trace("(Unopened) segment {} is no longer needed and will be deleted now", file);
FileUtils.deleteWithConfirm(file);
}
/**
* Adjust the tracked on-disk size. Called by individual segments to reflect writes, allocations and discards.
* @param addedSize
*/
void addSize(long addedSize)
{
size.addAndGet(addedSize);
}
/**
* @return the space (in bytes) used by all segment files.
*/
public long onDiskSize()
{
return size.get();
}
private long unusedCapacity()
{
long total = DatabaseDescriptor.getTotalCommitlogSpaceInMB() * 1024 * 1024;
long currentSize = size.get();
logger.trace("Total active commitlog segment space used is {} out of {}", currentSize, total);
return total - currentSize;
}
/**
* Force a flush on all CFs that are still dirty in @param segments.
*
* @return a Future that will finish when all the flushes are complete.
*/
private Future flushDataFrom(List segments, boolean force)
{
if (segments.isEmpty())
return Futures.immediateFuture(null);
final CommitLogPosition maxCommitLogPosition = segments.get(segments.size() - 1).getCurrentCommitLogPosition();
// a map of CfId -> forceFlush() to ensure we only queue one flush per cf
final Map> flushes = new LinkedHashMap<>();
for (CommitLogSegment segment : segments)
{
for (TableId dirtyTableId : segment.getDirtyTableIds())
{
TableMetadata metadata = Schema.instance.getTableMetadata(dirtyTableId);
if (metadata == null)
{
// even though we remove the schema entry before a final flush when dropping a CF,
// it's still possible for a writer to race and finish his append after the flush.
logger.trace("Marking clean CF {} that doesn't exist anymore", dirtyTableId);
segment.markClean(dirtyTableId, CommitLogPosition.NONE, segment.getCurrentCommitLogPosition());
}
else if (!flushes.containsKey(dirtyTableId))
{
final ColumnFamilyStore cfs = Keyspace.open(metadata.keyspace).getColumnFamilyStore(dirtyTableId);
// can safely call forceFlush here as we will only ever block (briefly) for other attempts to flush,
// no deadlock possibility since switchLock removal
flushes.put(dirtyTableId, force ? cfs.forceFlush() : cfs.forceFlush(maxCommitLogPosition));
}
}
}
return Futures.allAsList(flushes.values());
}
/**
* Stops CL, for testing purposes. DO NOT USE THIS OUTSIDE OF TESTS.
* Only call this after the AbstractCommitLogService is shut down.
*/
public void stopUnsafe(boolean deleteSegments)
{
logger.debug("CLSM closing and clearing existing commit log segments...");
shutdown();
try
{
awaitTermination();
}
catch (InterruptedException e)
{
throw new RuntimeException(e);
}
for (CommitLogSegment segment : activeSegments)
closeAndDeleteSegmentUnsafe(segment, deleteSegments);
activeSegments.clear();
size.set(0L);
logger.trace("CLSM done with closing and clearing existing commit log segments.");
}
/**
* To be used by tests only. Not safe if mutation slots are being allocated concurrently.
*/
@VisibleForTesting
public void awaitManagementTasksCompletion()
{
if (availableSegment == null && !atSegmentBufferLimit())
{
awaitAvailableSegment(allocatingFrom);
}
}
/**
* Explicitly for use only during resets in unit testing.
*/
private void closeAndDeleteSegmentUnsafe(CommitLogSegment segment, boolean delete)
{
try
{
discard(segment, delete);
}
catch (AssertionError ignored)
{
// segment file does not exist
}
}
/**
* Initiates the shutdown process for the management thread.
*/
public void shutdown()
{
assert !shutdown;
shutdown = true;
// Release the management thread and delete prepared segment.
// Do not block as another thread may claim the segment (this can happen during unit test initialization).
discardAvailableSegment();
wakeManager();
}
private void discardAvailableSegment()
{
CommitLogSegment next = null;
synchronized (this)
{
next = availableSegment;
availableSegment = null;
}
if (next != null)
next.discard(true);
}
/**
* Returns when the management thread terminates.
*/
public void awaitTermination() throws InterruptedException
{
if (managerThread != null)
{
managerThread.join();
managerThread = null;
}
for (CommitLogSegment segment : activeSegments)
segment.close();
if (bufferPool != null)
bufferPool.emptyBufferPool();
}
/**
* @return a read-only collection of the active commit log segments
*/
@VisibleForTesting
public Collection getActiveSegments()
{
return Collections.unmodifiableCollection(activeSegments);
}
/**
* @return the current CommitLogPosition of the active segment we're allocating from
*/
CommitLogPosition getCurrentPosition()
{
return allocatingFrom.getCurrentCommitLogPosition();
}
/**
* Requests commit log files sync themselves, if needed. This may or may not involve flushing to disk.
*
* @param flush Request that the sync operation flush the file to disk.
*/
public void sync(boolean flush) throws IOException
{
CommitLogSegment current = allocatingFrom;
for (CommitLogSegment segment : getActiveSegments())
{
// Do not sync segments that became active after sync started.
if (segment.id > current.id)
return;
segment.sync(flush);
}
}
/**
* Used by compressed and encrypted segments to share a buffer pool across the CLSM.
*/
SimpleCachedBufferPool getBufferPool()
{
return bufferPool;
}
void wakeManager()
{
managerThreadWaitQueue.signalAll();
}
/**
* Called by commit log segments when a buffer is freed to wake the management thread, which may be waiting for
* a buffer to become available.
*/
void notifyBufferFreed()
{
wakeManager();
}
/** Read-only access to current segment for subclasses. */
CommitLogSegment allocatingFrom()
{
return allocatingFrom;
}
}
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