/*
* 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.IOError;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.nio.MappedByteBuffer;
import java.util.Collection;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.zip.Checksum;
import java.util.HashMap;
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.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);
static final String FILENAME_PREFIX = "CommitLog-";
static final String FILENAME_EXTENSION = ".log";
private static final Pattern COMMIT_LOG_FILE_PATTERN = Pattern.compile(FILENAME_PREFIX + "(\\d+)" + FILENAME_EXTENSION);
// 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 HashMap<Integer, Integer> cfLastWrite = new HashMap<Integer, Integer>();
public final long id;
private final File logFile;
private RandomAccessFile logFileAccessor;
private boolean needsSync = false;
private final MappedByteBuffer buffer;
private boolean closed;
/**
* @return a newly minted segment file
*/
public static CommitLogSegment freshSegment()
{
return new CommitLogSegment(null);
}
/**
* 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 = System.nanoTime();
logFile = new File(DatabaseDescriptor.getCommitLogLocation(), FILENAME_PREFIX + id + FILENAME_EXTENSION);
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());
buffer.putInt(CommitLog.END_OF_SEGMENT_MARKER);
buffer.position(0);
needsSync = true;
}
catch (IOException e)
{
throw new IOError(e);
}
}
/**
* Extracts the commit log ID from filename
*
* @param filename the filename of the commit log file
* @return the extracted commit log ID
*/
public static long idFromFilename(String filename)
{
Matcher matcher = COMMIT_LOG_FILE_PATTERN.matcher(filename);
try
{
if (matcher.matches())
return Long.valueOf(matcher.group(1));
else
return -1L;
}
catch (NumberFormatException e)
{
return -1L;
}
}
/**
* @param filename the filename to check
* @return true if filename could be a commit log based on it's filename
*/
public static boolean possibleCommitLogFile(String filename)
{
return COMMIT_LOG_FILE_PATTERN.matcher(filename).matches();
}
/**
* 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();
try
{
if (deleteFile)
FileUtils.deleteWithConfirm(logFile);
}
catch (IOException e)
{
throw new IOError(e);
}
}
/**
* Recycle processes an unneeded segment file for reuse.
*
* @return a new CommitLogSegment representing the newly reusable segment.
*/
public CommitLogSegment recycle()
{
// writes an end-of-segment marker at the very beginning of the file and closes it
buffer.position(0);
buffer.putInt(CommitLog.END_OF_SEGMENT_MARKER);
buffer.position(0);
try
{
sync();
}
catch (IOException e)
{
// This is a best effort thing anyway
logger.warn("I/O error flushing " + this + " " + e);
}
close();
return new CommitLogSegment(getPath());
}
/**
* @return true if there is room to write() @param mutation to this segment
*/
public boolean hasCapacityFor(RowMutation mutation)
{
long totalSize = RowMutation.serializer().serializedSize(mutation, MessagingService.version_) + ENTRY_OVERHEAD_SIZE;
return totalSize <= 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 rowMutation the mutation to append to the commit log.
* @return the position of the appended mutation
*/
public ReplayPosition write(RowMutation rowMutation) throws IOException
{
assert !closed;
ReplayPosition repPos = getContext();
markDirty(rowMutation, repPos);
Checksum checksum = new PureJavaCrc32();
byte[] serializedRow = rowMutation.getSerializedBuffer(MessagingService.version_);
checksum.update(serializedRow.length);
buffer.putInt(serializedRow.length);
buffer.putLong(checksum.getValue());
buffer.put(serializedRow);
checksum.update(serializedRow, 0, serializedRow.length);
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 void sync() throws IOException
{
if (needsSync)
{
buffer.force();
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 void close()
{
if (closed)
return;
try
{
logFileAccessor.close();
closed = true;
}
catch (IOException e)
{
throw new IOError(e);
}
}
/**
* 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(Integer 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 void markClean(Integer 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 Collection<Integer> getDirtyCFIDs()
{
return cfLastWrite.keySet();
}
/**
* @return true if this segment is unused and safe to recycle or delete
*/
public 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 (Integer cfId : cfLastWrite.keySet())
{
CFMetaData m = Schema.instance.getCFMetaData(cfId);
sb.append(m == null ? "<deleted>" : m.cfName).append(" (").append(cfId).append("), ");
}
return sb.toString();
}
@Override
public String toString()
{
return "CommitLogSegment(" + getPath() + ')';
}
public int position()
{
return buffer.position();
}
}