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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.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.UUID;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.Future;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
import com.google.common.collect.Iterables;
import com.google.common.util.concurrent.*;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.config.Schema;
import org.apache.cassandra.db.ColumnFamilyStore;
import org.apache.cassandra.db.Keyspace;
import org.apache.cassandra.db.Mutation;
import org.apache.cassandra.io.util.FileUtils;
import org.apache.cassandra.utils.Pair;
import org.apache.cassandra.utils.concurrent.WaitQueue;
import org.apache.cassandra.utils.JVMStabilityInspector;
import org.apache.cassandra.utils.WrappedRunnable;
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 class CommitLogSegmentManager
{
static final Logger logger = LoggerFactory.getLogger(CommitLogSegmentManager.class);
/**
* Queue of work to be done by the manager thread, also used to wake the thread to perform segment allocation.
*/
private final BlockingQueue segmentManagementTasks = new LinkedBlockingQueue<>();
/** Segments that are ready to be used. Head of the queue is the one we allocate writes to */
private final ConcurrentLinkedQueue availableSegments = new ConcurrentLinkedQueue<>();
/** Active segments, containing unflushed data */
private final ConcurrentLinkedQueue activeSegments = new ConcurrentLinkedQueue<>();
/** The segment we are currently allocating commit log records to */
private volatile CommitLogSegment allocatingFrom = null;
private final WaitQueue hasAvailableSegments = new WaitQueue();
/**
* 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();
/**
* New segment creation is initially disabled because we'll typically get some "free" segments
* recycled after log replay.
*/
volatile boolean createReserveSegments = false;
private Thread managerThread;
private volatile boolean run = true;
private final CommitLog commitLog;
CommitLogSegmentManager(final CommitLog commitLog)
{
this.commitLog = commitLog;
}
void start()
{
// The run loop for the manager thread
Runnable runnable = new WrappedRunnable()
{
public void runMayThrow() throws Exception
{
while (run)
{
try
{
Runnable task = segmentManagementTasks.poll();
if (task == null)
{
// if we have no more work to do, check if we should create a new segment
if (availableSegments.isEmpty() && (activeSegments.isEmpty() || createReserveSegments))
{
logger.trace("No segments in reserve; creating a fresh one");
// TODO : some error handling in case we fail to create a new segment
availableSegments.add(CommitLogSegment.createSegment(commitLog));
hasAvailableSegments.signalAll();
}
// flush old Cfs if we're full
long unused = unusedCapacity();
if (unused < 0)
{
List segmentsToRecycle = new ArrayList<>();
long spaceToReclaim = 0;
for (CommitLogSegment segment : activeSegments)
{
if (segment == allocatingFrom)
break;
segmentsToRecycle.add(segment);
spaceToReclaim += DatabaseDescriptor.getCommitLogSegmentSize();
if (spaceToReclaim + unused >= 0)
break;
}
flushDataFrom(segmentsToRecycle, false);
}
try
{
// wait for new work to be provided
task = segmentManagementTasks.take();
}
catch (InterruptedException e)
{
throw new AssertionError();
}
}
task.run();
}
catch (Throwable t)
{
JVMStabilityInspector.inspectThrowable(t);
if (!CommitLog.handleCommitError("Failed managing commit log segments", t))
return;
// sleep some arbitrary period to avoid spamming CL
Uninterruptibles.sleepUninterruptibly(1, TimeUnit.SECONDS);
}
}
}
};
run = true;
managerThread = new Thread(runnable, "COMMIT-LOG-ALLOCATOR");
managerThread.start();
}
/**
* Reserve space in the current segment for the provided mutation or, if there isn't space available,
* create a new segment.
*
* @return the provided Allocation object
*/
public Allocation allocate(Mutation mutation, int size)
{
CommitLogSegment segment = allocatingFrom();
Allocation alloc;
while ( null == (alloc = segment.allocate(mutation, size)) )
{
// failed to allocate, so move to a new segment with enough room
advanceAllocatingFrom(segment);
segment = allocatingFrom;
}
return alloc;
}
// simple wrapper to ensure non-null value for allocatingFrom; only necessary on first call
CommitLogSegment allocatingFrom()
{
CommitLogSegment r = allocatingFrom;
if (r == null)
{
advanceAllocatingFrom(null);
r = allocatingFrom;
}
return r;
}
/**
* Fetches a new segment from the queue, creating a new one if necessary, and activates it
*/
private void advanceAllocatingFrom(CommitLogSegment old)
{
while (true)
{
CommitLogSegment next;
synchronized (this)
{
// do this in a critical section so we can atomically remove from availableSegments and add to allocatingFrom/activeSegments
// see https://issues.apache.org/jira/browse/CASSANDRA-6557?focusedCommentId=13874432&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13874432
if (allocatingFrom != old)
return;
next = availableSegments.poll();
if (next != null)
{
allocatingFrom = next;
activeSegments.add(next);
}
}
if (next != null)
{
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();
return;
}
// no more segments, so register to receive a signal when not empty
WaitQueue.Signal signal = hasAvailableSegments.register(commitLog.metrics.waitingOnSegmentAllocation.time());
// trigger the management thread; this must occur after registering
// the signal to ensure we are woken by any new segment creation
wakeManager();
// check if the queue has already been added to before waiting on the signal, to catch modifications
// that happened prior to registering the signal; *then* check to see if we've been beaten to making the change
if (!availableSegments.isEmpty() || allocatingFrom != old)
{
signal.cancel();
// if we've been beaten, just stop immediately
if (allocatingFrom != old)
return;
// otherwise try again, as there should be an available segment
continue;
}
// can only reach here if the queue hasn't been inserted into
// before we registered the signal, as we only remove items from the queue
// after updating allocatingFrom. Can safely block until we are signalled
// by the allocator that new segments have been published
signal.awaitUninterruptibly();
}
}
private void wakeManager()
{
// put a NO-OP on the queue, to trigger management thread (and create a new segment if necessary)
segmentManagementTasks.add(Runnables.doNothing());
}
/**
* 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 recycles
* the segments
*/
void forceRecycleAll(Iterable droppedCfs)
{
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
// on the relevant keyspaces to complete
Set keyspaces = new HashSet<>();
for (UUID cfId : last.getDirtyCFIDs())
{
ColumnFamilyStore cfs = Schema.instance.getColumnFamilyStoreInstance(cfId);
if (cfs != null)
keyspaces.add(cfs.keyspace);
}
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 (UUID cfId : droppedCfs)
segment.markClean(cfId, segment.getContext());
// 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())
recycleSegment(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 and return false, indicating that we failed
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 recycled.
*
* @param segment segment that is no longer in use
*/
void recycleSegment(final CommitLogSegment segment)
{
boolean archiveSuccess = commitLog.archiver.maybeWaitForArchiving(segment.getName());
if (activeSegments.remove(segment))
{
// if archiving (command) was not successful then leave the file alone. don't delete or recycle.
discardSegment(segment, archiveSuccess);
}
else
{
logger.warn("segment {} not found in activeSegments queue", segment);
}
}
/**
* Differs from the above because it can work on any file instead of just existing
* commit log segments managed by this manager.
*
* @param file segment file that is no longer in use.
*/
void recycleSegment(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);
}
/**
* Indicates that a segment file should be deleted.
*
* @param segment segment to be discarded
*/
private void discardSegment(final CommitLogSegment segment, final boolean deleteFile)
{
logger.trace("Segment {} is no longer active and will be deleted {}", segment, deleteFile ? "now" : "by the archive script");
segmentManagementTasks.add(new Runnable()
{
public void run()
{
segment.discard(deleteFile);
}
});
}
/**
* 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;
}
/**
* @param name the filename to check
* @return true if file is managed by this manager.
*/
public boolean manages(String name)
{
for (CommitLogSegment segment : Iterables.concat(activeSegments, availableSegments))
if (segment.getName().equals(name))
return true;
return false;
}
/**
* Throws a flag that enables the behavior of keeping at least one spare segment
* available at all times.
*/
void enableReserveSegmentCreation()
{
createReserveSegments = true;
wakeManager();
}
/**
* 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 ReplayPosition maxReplayPosition = segments.get(segments.size() - 1).getContext();
// a map of CfId -> forceFlush() to ensure we only queue one flush per cf
final Map> flushes = new LinkedHashMap<>();
for (CommitLogSegment segment : segments)
{
for (UUID dirtyCFId : segment.getDirtyCFIDs())
{
Pair pair = Schema.instance.getCF(dirtyCFId);
if (pair == 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", dirtyCFId);
segment.markClean(dirtyCFId, segment.getContext());
}
else if (!flushes.containsKey(dirtyCFId))
{
String keyspace = pair.left;
final ColumnFamilyStore cfs = Keyspace.open(keyspace).getColumnFamilyStore(dirtyCFId);
// 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(dirtyCFId, force ? cfs.forceFlush() : cfs.forceFlush(maxReplayPosition));
}
}
}
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.trace("CLSM closing and clearing existing commit log segments...");
createReserveSegments = false;
awaitManagementTasksCompletion();
shutdown();
try
{
awaitTermination();
}
catch (InterruptedException e)
{
throw new RuntimeException(e);
}
for (CommitLogSegment segment : activeSegments)
closeAndDeleteSegmentUnsafe(segment, deleteSegments);
activeSegments.clear();
for (CommitLogSegment segment : availableSegments)
closeAndDeleteSegmentUnsafe(segment, deleteSegments);
availableSegments.clear();
allocatingFrom = null;
segmentManagementTasks.clear();
size.set(0L);
logger.trace("CLSM done with closing and clearing existing commit log segments.");
}
// Used by tests only.
void awaitManagementTasksCompletion()
{
while (!segmentManagementTasks.isEmpty())
Thread.yield();
// The last management task is not yet complete. Wait a while for it.
Uninterruptibles.sleepUninterruptibly(100, TimeUnit.MILLISECONDS);
// TODO: If this functionality is required by anything other than tests, signalling must be used to ensure
// waiting completes correctly.
}
private static void closeAndDeleteSegmentUnsafe(CommitLogSegment segment, boolean delete)
{
try
{
segment.discard(delete);
}
catch (AssertionError ignored)
{
// segment file does not exist
}
}
/**
* Initiates the shutdown process for the management thread.
*/
public void shutdown()
{
run = false;
wakeManager();
}
/**
* Returns when the management thread terminates.
*/
public void awaitTermination() throws InterruptedException
{
managerThread.join();
for (CommitLogSegment segment : activeSegments)
segment.close();
for (CommitLogSegment segment : availableSegments)
segment.close();
CompressedSegment.shutdown();
}
/**
* @return a read-only collection of the active commit log segments
*/
Collection getActiveSegments()
{
return Collections.unmodifiableCollection(activeSegments);
}
}