/// <summary>
/// Rotates the current log file, continuing into next (version) log file.
/// This method must be recovery safe, which means a crash at any point should be recoverable.
/// Concurrent readers must also be able to parry for concurrent rotation.
/// Concurrent writes will not be an issue since rotation and writing contends on the same monitor.
///
/// Steps during rotation are:
/// <ol>
/// <li>1: Increment log version, <seealso cref="LogVersionRepository.incrementAndGetVersion()"/> (also flushes the store)</li>
/// <li>2: Flush current log</li>
/// <li>3: Create new log file</li>
/// <li>4: Write header</li>
/// </ol>
///
/// Recovery: what happens if crash between:
/// <ol>
/// <li>1-2: New log version has been set, starting the writer will create the new log file idempotently.
/// At this point there may have been half-written transactions in the previous log version,
/// although they haven't been considered committed and so they will be truncated from log during recovery</li>
/// <li>2-3: New log version has been set, starting the writer will create the new log file idempotently.
/// At this point there may be complete transactions in the previous log version which may not have been
/// acknowledged to be committed back to the user, but will be considered committed anyway.</li>
/// <li>3-4: New log version has been set, starting the writer will see that the new file exists and
/// will be forgiving when trying to read the header of it, so that if it isn't complete a fresh
/// header will be set.</li>
/// </ol>
///
/// Reading: what happens when rotation is between:
/// <ol>
/// <li>1-2: Reader bridge will see that there's a new version (when asking <seealso cref="LogVersionRepository"/>
/// and try to open it. The log file doesn't exist yet though. The bridge can parry for this by catching
/// <seealso cref="FileNotFoundException"/> and tell the reader that the stream has ended</li>
/// <li>2-3: Same as (1-2)</li>
/// <li>3-4: Here the new log file exists, but the header may not be fully written yet.
/// the reader will fail when trying to read the header since it's reading it strictly and bridge
/// catches that exception, treating it the same as if the file didn't exist.</li>
/// </ol>
/// </summary>
/// <param name="currentLog"> current <seealso cref="LogVersionedStoreChannel channel"/> to flush and close. </param>
/// <returns> the channel of the newly opened/created log file. </returns>
/// <exception cref="IOException"> if an error regarding closing or opening log files occur. </exception>
//JAVA TO C# CONVERTER WARNING: Method 'throws' clauses are not available in C#:
//ORIGINAL LINE: private org.neo4j.kernel.impl.transaction.log.PhysicalLogVersionedStoreChannel rotate(org.neo4j.kernel.impl.transaction.log.LogVersionedStoreChannel currentLog) throws java.io.IOException
private PhysicalLogVersionedStoreChannel Rotate(LogVersionedStoreChannel currentLog)
{
/*
* The store is now flushed. If we fail now the recovery code will open the
* current log file and replay everything. That's unnecessary but totally ok.
*/
long newLogVersion = _logVersionRepository.incrementAndGetVersion();
/*
* Rotation can happen at any point, although not concurrently with an append,
* although an append may have (most likely actually) left at least some bytes left
* in the buffer for future flushing. Flushing that buffer now makes the last appended
* transaction complete in the log we're rotating away. Awesome.
*/
_writer.prepareForFlush().flush();
/*
* The log version is now in the store, flushed and persistent. If we crash
* now, on recovery we'll attempt to open the version we're about to create
* (but haven't yet), discover it's not there. That will lead to creating
* the file, setting the header and continuing.
* We using committing transaction id as a source of last transaction id here since
* we can have transactions that are not yet published as committed but were already stored
* into transaction log that was just rotated.
*/
PhysicalLogVersionedStoreChannel newLog = _logFiles.createLogChannelForVersion(newLogVersion, OpenMode.READ_WRITE, _context.committingTransactionId);
currentLog.close();
return(newLog);
}
//JAVA TO C# CONVERTER WARNING: Method 'throws' clauses are not available in C#:
//ORIGINAL LINE: public LogVersionedStoreChannel next(LogVersionedStoreChannel channel) throws java.io.IOException
public override LogVersionedStoreChannel Next(LogVersionedStoreChannel channel)
{
PhysicalLogVersionedStoreChannel nextChannel;
try
{
nextChannel = _logFiles.openForVersion(channel.Version + 1);
}
catch (Exception e) when(e is FileNotFoundException || e is IncompleteLogHeaderException)
{
// See PhysicalLogFile#rotate() for description as to why these exceptions are OK
return(channel);
}
channel.close();
return(nextChannel);
}
/// <summary>
/// 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.
/// </summary>
/// <param name="initialPosition"> <seealso cref="LogPosition"/> to start scan from. </param>
/// <param name="maxLogVersion"> max log version to scan. </param>
/// <returns> value object that contains first transaction id of closes commit entry to {@code initialPosition},
/// or <seealso cref="LogTailInformation.NO_TRANSACTION_ID"/> if not found. And failure flag that will be set to true if
/// there was some exception during transaction log processing. </returns>
/// <exception cref="IOException"> on channel close I/O error. </exception>
//JAVA TO C# CONVERTER WARNING: Method 'throws' clauses are not available in C#:
//ORIGINAL LINE: protected ExtractedTransactionRecord extractFirstTxIdAfterPosition(org.neo4j.kernel.impl.transaction.log.LogPosition initialPosition, long maxLogVersion) throws java.io.IOException
protected internal virtual ExtractedTransactionRecord ExtractFirstTxIdAfterPosition(LogPosition initialPosition, long maxLogVersion)
{
LogPosition currentPosition = initialPosition;
while (currentPosition.LogVersion <= maxLogVersion)
{
LogVersionedStoreChannel storeChannel = TryOpenStoreChannel(currentPosition);
if (storeChannel != null)
{
try
{
storeChannel.Position(currentPosition.ByteOffset);
using (ReadAheadLogChannel logChannel = new ReadAheadLogChannel(storeChannel), LogEntryCursor cursor = new LogEntryCursor(_logEntryReader, logChannel))
{
while (cursor.Next())
{
LogEntry entry = cursor.Get();
if (entry is LogEntryCommit)
{
return(new ExtractedTransactionRecord((( LogEntryCommit )entry).TxId));
}
}
}
}
catch (Exception t)
{
_monitor.corruptedLogFile(currentPosition.LogVersion, t);
return(new ExtractedTransactionRecord(true));
}
finally
{
storeChannel.close();
}
}
currentPosition = LogPosition.start(currentPosition.LogVersion + 1);
}
return(new ExtractedTransactionRecord());
}