org.apache.cassandra.db.commitlog.CommitLogSegment Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
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* 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.DataOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.zip.Checksum;
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.ColumnFamily;
import org.apache.cassandra.db.RowMutation;
import org.apache.cassandra.io.FSWriteError;
import org.apache.cassandra.io.util.ByteBufferOutputStream;
import org.apache.cassandra.io.util.ChecksummedOutputStream;
import org.apache.cassandra.io.util.FileUtils;
import org.apache.cassandra.net.MessagingService;
import org.apache.cassandra.utils.PureJavaCrc32;
/*
* A single commit log file on disk. Manages creation of the file and writing row 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 class CommitLogSegment
{
private static final Logger logger = LoggerFactory.getLogger(CommitLogSegment.class);
private final static long idBase = System.currentTimeMillis();
private final static AtomicInteger nextId = new AtomicInteger(1);
// The commit log entry overhead in bytes (int: length + long: head checksum + long: tail checksum)
static final int ENTRY_OVERHEAD_SIZE = 4 + 8 + 8;
// cache which cf is dirty in this segment to avoid having to lookup all ReplayPositions to decide if we can delete this segment
private final Map cfLastWrite = new HashMap<>();
public final long id;
private final File logFile;
private final RandomAccessFile logFileAccessor;
private boolean needsSync = false;
private final MappedByteBuffer buffer;
private final Checksum checksum;
private final DataOutputStream bufferStream;
private boolean closed;
public final CommitLogDescriptor descriptor;
/**
* @return a newly minted segment file
*/
public static CommitLogSegment freshSegment()
{
return new CommitLogSegment(null);
}
public 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(String filePath)
{
id = getNextId();
descriptor = new CommitLogDescriptor(id);
logFile = new File(DatabaseDescriptor.getCommitLogLocation(), descriptor.fileName());
boolean isCreating = true;
try
{
if (filePath != null)
{
File oldFile = new File(filePath);
if (oldFile.exists())
{
logger.debug("Re-using discarded CommitLog segment for {} from {}", id, filePath);
if (!oldFile.renameTo(logFile))
throw new IOException("Rename from " + filePath + " to " + id + " failed");
isCreating = false;
}
}
// Open the initial the segment file
logFileAccessor = new RandomAccessFile(logFile, "rw");
if (isCreating)
logger.debug("Creating new commit log segment {}", logFile.getPath());
// Map the segment, extending or truncating it to the standard segment size
logFileAccessor.setLength(DatabaseDescriptor.getCommitLogSegmentSize());
buffer = logFileAccessor.getChannel().map(FileChannel.MapMode.READ_WRITE, 0, DatabaseDescriptor.getCommitLogSegmentSize());
checksum = new PureJavaCrc32();
bufferStream = new DataOutputStream(new ChecksummedOutputStream(new ByteBufferOutputStream(buffer), checksum));
buffer.putInt(CommitLog.END_OF_SEGMENT_MARKER);
buffer.position(0);
needsSync = true;
sync();
}
catch (IOException e)
{
throw new FSWriteError(e, logFile);
}
}
/**
* Completely discards a segment file by deleting it. (Potentially blocking operation)
*/
public void discard(boolean deleteFile)
{
// TODO shouldn't we close the file when we're done writing to it, which comes (potentially) much earlier than it's eligible for recyling?
close();
// it's safe to simply try (and maybe fail) to delete the log file because we should only ever close()/discard() once
// the global ReplayPosition is past the current log file position, so we will never replay it; however to be on the
// safe side we attempt to rename/zero it if delete fails
if (deleteFile)
{
try
{
FileUtils.deleteWithConfirm(logFile);
}
catch (FSWriteError e)
{
// attempt to rename the file and zero its start, if possible, before throwing the error
File file = logFile;
try
{
File newFile = new File(file.getPath() + ".discarded");
FileUtils.renameWithConfirm(file, newFile);
file = newFile;
}
catch (Throwable t)
{
}
try
{
RandomAccessFile raf = new RandomAccessFile(file, "rw");
ByteBuffer write = ByteBuffer.allocate(8);
write.putInt(CommitLog.END_OF_SEGMENT_MARKER);
write.position(0);
raf.getChannel().write(write);
raf.close();
logger.error("{} {}, as we failed to delete it.", file == logFile ? "Zeroed" : "Renamed and zeroed", file);
}
catch (Throwable t)
{
if (logFile == file)
{
logger.error("Could not rename or zero {}, which we also failed to delete. In the face of other issues this could result in unnecessary log replay.", t, file);
}
else
{
logger.error("Renamed {} to {}, as we failed to delete it, however we failed to zero its header.", t, logFile, file);
}
}
throw e;
}
}
}
/**
* Recycle processes an unneeded segment file for reuse.
*
* @return a new CommitLogSegment representing the newly reusable segment.
*/
public CommitLogSegment recycle()
{
close();
return new CommitLogSegment(getPath());
}
/**
* @return true if there is room to write() @param size to this segment
*/
public boolean hasCapacityFor(long size)
{
return size <= buffer.remaining();
}
/**
* mark all of the column families we're modifying as dirty at this position
*/
private void markDirty(RowMutation rowMutation, ReplayPosition repPos)
{
for (ColumnFamily columnFamily : rowMutation.getColumnFamilies())
{
// check for null cfm in case a cl write goes through after the cf is
// defined but before a new segment is created.
CFMetaData cfm = Schema.instance.getCFMetaData(columnFamily.id());
if (cfm == null)
{
logger.error("Attempted to write commit log entry for unrecognized column family: " + columnFamily.id());
}
else
{
markCFDirty(cfm.cfId, repPos.position);
}
}
}
/**
* Appends a row mutation onto the commit log. Requres that hasCapacityFor has already been checked.
*
* @param mutation the mutation to append to the commit log.
* @return the position of the appended mutation
*/
public ReplayPosition write(RowMutation mutation) throws IOException
{
assert !closed;
ReplayPosition repPos = getContext();
markDirty(mutation, repPos);
checksum.reset();
// checksummed length
int length = (int) RowMutation.serializer.serializedSize(mutation, MessagingService.current_version);
bufferStream.writeInt(length);
buffer.putLong(checksum.getValue());
// checksummed mutation
RowMutation.serializer.serialize(mutation, bufferStream, MessagingService.current_version);
buffer.putLong(checksum.getValue());
if (buffer.remaining() >= 4)
{
// writes end of segment marker and rewinds back to position where it starts
buffer.putInt(CommitLog.END_OF_SEGMENT_MARKER);
buffer.position(buffer.position() - CommitLog.END_OF_SEGMENT_MARKER_SIZE);
}
needsSync = true;
return repPos;
}
/**
* Forces a disk flush for this segment file.
*/
public synchronized void sync()
{
if (needsSync)
{
try
{
buffer.force();
}
catch (Exception e) // MappedByteBuffer.force() does not declare IOException but can actually throw it
{
throw new FSWriteError(e, getPath());
}
needsSync = false;
}
}
/**
* @return the current ReplayPosition for this log segment
*/
public ReplayPosition getContext()
{
return new ReplayPosition(id, buffer.position());
}
/**
* @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();
}
/**
* Close the segment file.
*/
public synchronized void close()
{
if (closed)
return;
needsSync = false;
try
{
FileUtils.clean(buffer);
logFileAccessor.close();
closed = true;
}
catch (IOException e)
{
throw new FSWriteError(e, getPath());
}
}
/**
* Records the CF as dirty at a certain position.
*
* @param cfId the column family ID that is now dirty
* @param position the position the last write for this CF was written at
*/
private void markCFDirty(UUID cfId, Integer position)
{
cfLastWrite.put(cfId, position);
}
/**
* 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 context)
{
Integer lastWritten = cfLastWrite.get(cfId);
if (lastWritten != null && (!contains(context) || lastWritten < context.position))
{
cfLastWrite.remove(cfId);
}
}
/**
* @return a collection of dirty CFIDs for this segment file.
*/
public synchronized Collection getDirtyCFIDs()
{
return new ArrayList<>(cfLastWrite.keySet());
}
/**
* @return true if this segment is unused and safe to recycle or delete
*/
public synchronized boolean isUnused()
{
return cfLastWrite.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 ? "" : m.cfName).append(" (").append(cfId).append("), ");
}
return sb.toString();
}
@Override
public String toString()
{
return "CommitLogSegment(" + getPath() + ')';
}
public int position()
{
return buffer.position();
}
public static class CommitLogSegmentFileComparator implements Comparator
{
public int compare(File f, File f2)
{
CommitLogDescriptor desc = CommitLogDescriptor.fromFileName(f.getName());
CommitLogDescriptor desc2 = CommitLogDescriptor.fromFileName(f2.getName());
return (int) (desc.id - desc2.id);
}
}
}
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