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LogTailScanner.java
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LogTailScanner.java
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/*
* Copyright (c) 2002-2017 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.kernel.impl.transaction.log;
import java.io.IOException;
import org.neo4j.helpers.Exceptions;
import org.neo4j.io.fs.FileSystemAbstraction;
import org.neo4j.kernel.impl.logging.LogService;
import org.neo4j.kernel.impl.store.UnderlyingStorageException;
import org.neo4j.kernel.impl.transaction.log.entry.CheckPoint;
import org.neo4j.kernel.impl.transaction.log.entry.LogEntry;
import org.neo4j.kernel.impl.transaction.log.entry.LogEntryCommit;
import org.neo4j.kernel.impl.transaction.log.entry.LogEntryReader;
import org.neo4j.kernel.impl.transaction.log.entry.LogEntryStart;
import org.neo4j.kernel.impl.transaction.log.entry.LogEntryVersion;
import org.neo4j.kernel.impl.transaction.log.entry.UnsupportedLogVersionException;
import org.neo4j.logging.Log;
import org.neo4j.unsafe.impl.internal.dragons.FeatureToggles;
import static java.lang.String.format;
import static org.neo4j.kernel.impl.transaction.log.LogVersionRepository.INITIAL_LOG_VERSION;
/**
* This class collects information about the latest entries in the transaction log. Since the only way we have to collect
* said information is to scan the transaction log from beginning to end, which is costly, we do this once and save the
* result for others to consume.
* <p>
* Due to the nature of transaction logs and log rotation, a single transaction log file has to be scanned forward, and
* if the required data is not found we search backwards through log file versions.
*/
public class LogTailScanner
{
private final PhysicalLogFiles logFiles;
private final FileSystemAbstraction fileSystem;
private final LogEntryReader<ReadableClosablePositionAwareChannel> logEntryReader;
private LogTailInformation logTailInformation;
private final Log log;
public LogTailScanner( PhysicalLogFiles logFiles, FileSystemAbstraction fileSystem,
LogEntryReader<ReadableClosablePositionAwareChannel> logEntryReader, LogService logService )
{
this.logFiles = logFiles;
this.fileSystem = fileSystem;
this.logEntryReader = logEntryReader;
this.log = logService.getInternalLog( LogTailScanner.class );
}
private LogTailInformation findLogTail() throws IOException
{
final long fromVersionBackwards = logFiles.getHighestLogVersion();
long version = fromVersionBackwards;
long versionToSearchForCommits = fromVersionBackwards;
LogEntryStart latestStartEntry = null;
LogEntryStart oldestStartEntry = null;
long oldestVersionFound = -1;
LogEntryVersion latestLogEntryVersion = null;
boolean commitsAfterCheckPoint = false;
while ( version >= INITIAL_LOG_VERSION )
{
LogVersionedStoreChannel channel =
PhysicalLogFile.tryOpenForVersion( logFiles, fileSystem, version, false );
if ( channel == null )
{
break;
}
oldestVersionFound = version;
CheckPoint latestCheckPoint = null;
ReadableLogChannel recoveredDataChannel = new ReadAheadLogChannel( channel );
boolean firstStartEntry = true;
try ( LogEntryCursor cursor = new LogEntryCursor( logEntryReader, recoveredDataChannel ) )
{
LogEntry entry;
while ( cursor.next() )
{
entry = cursor.get();
// Collect data about latest checkpoint
if ( entry instanceof CheckPoint )
{
latestCheckPoint = entry.as();
}
// Collect data about latest commits
if ( entry instanceof LogEntryStart )
{
LogEntryStart startEntry = entry.as();
if ( version == versionToSearchForCommits )
{
latestStartEntry = startEntry;
}
// The scan goes backwards by log version, although forward per log version
// Oldest start entry will be the first in the last log version scanned.
if ( firstStartEntry )
{
oldestStartEntry = startEntry;
firstStartEntry = false;
}
}
// Collect data about latest entry version, only in first log file
if ( version == versionToSearchForCommits || latestLogEntryVersion == null )
{
latestLogEntryVersion = entry.getVersion();
}
}
}
catch ( Throwable t )
{
if ( Exceptions.contains( t, UnsupportedLogVersionException.class ) )
{
if ( FeatureToggles.flag( LogTailScanner.class, "force", false ) )
{
log.warn( "Unsupported log version was found in transactional logs, but log processing was " +
"forced.", t );
}
else
{
throw new RuntimeException( format( "Unsupported transaction log version found. " +
"To force transactional processing anyway and trip non recognised transactions please " +
"use %s. By using this flag you can lose part of your transactions log. This operation is irretrievable." +
" ", FeatureToggles.toggle( LogTailScanner.class, "force", true ) ), t );
}
}
log.warn( format( "Fail to read transaction log version %d.", version ), t );
commitsAfterCheckPoint = true;
}
if ( latestCheckPoint != null )
{
return latestCheckPoint( fromVersionBackwards, version, latestStartEntry, oldestVersionFound,
latestCheckPoint, latestLogEntryVersion, commitsAfterCheckPoint );
}
version--;
// if we have found no commits in the latest log, keep searching in the next one
if ( latestStartEntry == null )
{
versionToSearchForCommits--;
}
}
commitsAfterCheckPoint |= oldestStartEntry != null;
long firstTxAfterPosition = (commitsAfterCheckPoint && oldestStartEntry != null)
? extractFirstTxIdAfterPosition( oldestStartEntry.getStartPosition(), fromVersionBackwards )
: LogTailInformation.NO_TRANSACTION_ID;
return new LogTailInformation( null, commitsAfterCheckPoint, firstTxAfterPosition, oldestVersionFound,
fromVersionBackwards, latestLogEntryVersion );
}
protected LogTailInformation latestCheckPoint( long fromVersionBackwards, long version,
LogEntryStart latestStartEntry, long oldestVersionFound, CheckPoint latestCheckPoint,
LogEntryVersion latestLogEntryVersion, boolean commitsAfterCheckPoint ) throws IOException
{
// Is the latest start entry in this log file version later than what the latest check point targets?
LogPosition target = latestCheckPoint.getLogPosition();
boolean startEntryAfterCheckPoint = ((latestStartEntry != null) &&
(latestStartEntry.getStartPosition().compareTo( target ) >= 0)) ||
commitsAfterCheckPoint;
if ( !startEntryAfterCheckPoint )
{
if ( target.getLogVersion() < version )
{
// This check point entry targets a previous log file.
// Go there and see if there's a transaction. Reader is capped to that log version.
try
{
startEntryAfterCheckPoint =
extractFirstTxIdAfterPosition( target, version ) != LogTailInformation.NO_TRANSACTION_ID;
}
catch ( LogReadingException lre )
{
startEntryAfterCheckPoint = true;
}
}
}
// Extract first transaction id after check point target position.
// Reader may continue into log files after the initial version.
long firstTxIdAfterCheckPoint = LogTailInformation.NO_TRANSACTION_ID;
if ( startEntryAfterCheckPoint )
{
try
{
firstTxIdAfterCheckPoint = extractFirstTxIdAfterPosition( target, fromVersionBackwards );
}
catch ( LogReadingException lre )
{
//
}
}
return new LogTailInformation( latestCheckPoint, startEntryAfterCheckPoint,
firstTxIdAfterCheckPoint, oldestVersionFound, fromVersionBackwards, latestLogEntryVersion );
}
/**
* Extracts txId from first commit entry, when starting reading at the given {@code position}.
* If no commit entry found in the version, the reader will continue into next version(s) up till
* {@code maxLogVersion} until finding one.
*
* @param initialPosition {@link LogPosition} to start scan from.
* @param maxLogVersion max log version to scan.
* @return txId of closes commit entry to {@code initialPosition}, or {@link LogTailInformation#NO_TRANSACTION_ID}
* if not found.
* @throws IOException on I/O error.
*/
protected long extractFirstTxIdAfterPosition( LogPosition initialPosition, long maxLogVersion ) throws IOException
{
LogPosition currentPosition = initialPosition;
while ( currentPosition.getLogVersion() <= maxLogVersion )
{
LogVersionedStoreChannel storeChannel = PhysicalLogFile.tryOpenForVersion( logFiles, fileSystem,
currentPosition.getLogVersion(), false );
if ( storeChannel != null )
{
try
{
storeChannel.position( currentPosition.getByteOffset() );
try ( ReadAheadLogChannel logChannel = new ReadAheadLogChannel( storeChannel );
LogEntryCursor cursor = new LogEntryCursor( logEntryReader, logChannel ) )
{
while ( cursor.next() )
{
LogEntry entry = cursor.get();
if ( entry instanceof LogEntryCommit )
{
return ((LogEntryCommit) entry).getTxId();
}
}
}
catch ( Throwable t )
{
log.warn( format( "Fail to read transaction log version %d.", currentPosition.getLogVersion() ), t );
throw new LogReadingException(
new LogPosition( currentPosition.getLogVersion(), storeChannel.position() ) );
}
}
finally
{
storeChannel.close();
}
}
currentPosition = LogPosition.start( currentPosition.getLogVersion() + 1 );
}
return LogTailInformation.NO_TRANSACTION_ID;
}
/**
* Collects information about the tail of the transaction log, i.e. last checkpoint, last entry etc.
* Since this is an expensive task we do it once and reuse the result. This method is thus lazy and the first one
* calling it will take the hit.
* <p>
* This is only intended to be used during startup. If you need to track the state of the tail, that can be done more
* efficiently at runtime, and this method should then only be used to restore said state.
*
* @return snapshot of the state of the transaction logs tail at startup.
* @throws UnderlyingStorageException if any errors occurs while parsing the transaction logs
*/
public LogTailInformation getTailInformation() throws UnderlyingStorageException
{
if ( logTailInformation == null )
{
try
{
logTailInformation = findLogTail();
}
catch ( IOException e )
{
throw new UnderlyingStorageException( "Error encountered while parsing transaction logs", e );
}
}
return logTailInformation;
}
public static class LogTailInformation
{
public static long NO_TRANSACTION_ID = -1;
public final CheckPoint lastCheckPoint;
public final boolean commitsAfterLastCheckPoint;
public final long firstTxIdAfterLastCheckPoint;
public final long oldestLogVersionFound;
public final long currentLogVersion;
public final LogEntryVersion latestLogEntryVersion;
public LogTailInformation( CheckPoint lastCheckPoint, boolean commitsAfterLastCheckPoint,
long firstTxIdAfterLastCheckPoint, long oldestLogVersionFound, long currentLogVersion, LogEntryVersion latestLogEntryVersion )
{
this.lastCheckPoint = lastCheckPoint;
this.commitsAfterLastCheckPoint = commitsAfterLastCheckPoint;
this.firstTxIdAfterLastCheckPoint = firstTxIdAfterLastCheckPoint;
this.oldestLogVersionFound = oldestLogVersionFound;
this.currentLogVersion = currentLogVersion;
this.latestLogEntryVersion = latestLogEntryVersion;
}
}
private class LogReadingException extends RuntimeException
{
private LogPosition logPosition;
LogReadingException( LogPosition logPosition )
{
this.logPosition = logPosition;
}
public LogPosition getLogPosition()
{
return logPosition;
}
}
}