org.exist.storage.journal
Class Journal

java.lang.Object
  org.exist.storage.journal.Journal

public class Journal
extends Object

Manages the journalling log. The database uses one central journal for all data files. If the journal exceeds the predefined maximum size, a new file is created. Every journal file has a unique number, which keeps growing during the lifetime of the db. The name of the file corresponds to the file number. The file with the highest number will be used for recovery. A buffer is used to temporarily buffer journal entries. To guarantee consistency, the buffer will be flushed and the journal is synched after every commit or whenever a db page is written to disk. Each entry has the structure:

[byte: entryType, long: transactionId, short length, byte[] data, short backLink]

• entryType is a unique id that identifies the log record. Entry types are registered via the LogEntryTypes class.
• transactionId: the id of the transaction that created the record.
• length: the length of the log entry data.
• data: the payload data provided by the Loggable object.
• backLink: offset to the start of the record. Used when scanning the log file backwards.

Author:

wolf

Field Summary

static String	BAK_FILE_SUFFIX
static int	DEFAULT_MAX_SIZE default maximum journal size
static String	LCK_FILE
static int	LOG_ENTRY_BASE_LEN header length + trailing back link
static int	LOG_ENTRY_HEADER_LEN the length of the header of each entry: entryType + transactionId + length
static String	LOG_FILE_SUFFIX

Constructor Summary

Journal(BrokerPool pool, File directory)

Method Summary

void	checkpoint(long txnId, boolean switchLogFiles) Write a checkpoint record to the journal and flush it.
void	close()
static int	findLastFile(File[] files) Find the journal file with the highest file number.
void	flushToLog(boolean fsync) Flush the current buffer to disk.
void	flushToLog(boolean fsync, boolean forceSync) Flush the current buffer to disk.
File	getFile(int fileNum) Returns the file corresponding to the specified file number.
File[]	getFiles() Returns all journal files found in the data directory.
void	initialize()
long	lastWrittenLsn() Returns the last LSN physically written to the journal.
void	setCurrentFileNum(int fileNum) Set the file number of the last file used.
void	setInRecovery(boolean value) Called to signal that the db is currently in recovery phase, so no output should be written.
void	shutdown(long txnId) Shut down the journal.
void	switchFiles() Create a new journal with a larger file number than the previous file.
void	writeToLog(Loggable loggable) Write a log entry to the journalling log.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

LOG_FILE_SUFFIX

public static final String LOG_FILE_SUFFIX

See Also:

Constant Field Values

BAK_FILE_SUFFIX

public static final String BAK_FILE_SUFFIX

See Also:

Constant Field Values

LCK_FILE

public static final String LCK_FILE

See Also:

Constant Field Values

LOG_ENTRY_HEADER_LEN

public static final int LOG_ENTRY_HEADER_LEN

the length of the header of each entry: entryType + transactionId + length

See Also:

Constant Field Values

LOG_ENTRY_BASE_LEN

public static final int LOG_ENTRY_BASE_LEN

header length + trailing back link

See Also:

Constant Field Values

DEFAULT_MAX_SIZE

public static final int DEFAULT_MAX_SIZE

default maximum journal size

See Also:

Constant Field Values

Constructor Detail

Journal

public Journal(BrokerPool pool,
               File directory)
        throws EXistException

Throws:

EXistException

Method Detail

initialize

public void initialize()
                throws EXistException,
                       ReadOnlyException

Throws:

EXistException

ReadOnlyException

writeToLog

public void writeToLog(Loggable loggable)
                throws TransactionException

Write a log entry to the journalling log.

Parameters:

loggable -

Throws:

TransactionException

lastWrittenLsn

public long lastWrittenLsn()

Returns the last LSN physically written to the journal.

Returns:

last written LSN

flushToLog

public void flushToLog(boolean fsync)

Flush the current buffer to disk. If fsync is true, a sync will be called on the file to force all changes to disk.

Parameters:

fsync - forces all changes to disk if true and syncMode is set to SYNC_ON_COMMIT.

flushToLog

public void flushToLog(boolean fsync,
                       boolean forceSync)

Flush the current buffer to disk. If fsync is true, a sync will be called on the file to force all changes to disk.

Parameters:

fsync - forces all changes to disk if true and syncMode is set to SYNC_ON_COMMIT.

forceSync - force changes to disk even if syncMode doesn't require it.

checkpoint

public void checkpoint(long txnId,
                       boolean switchLogFiles)
                throws TransactionException

Write a checkpoint record to the journal and flush it. If switchLogFiles is true, a new journal will be started, but only if the file is larger than MIN_REPLACE. The old log is removed.

Parameters:

txnId -

switchLogFiles -

Throws:

TransactionException

setCurrentFileNum

public void setCurrentFileNum(int fileNum)

Set the file number of the last file used.

Parameters:

fileNum - the log file number

switchFiles

public void switchFiles()
                 throws LogException

Create a new journal with a larger file number than the previous file.

Throws:

LogException

close

public void close()

findLastFile

public static final int findLastFile(File[] files)

Find the journal file with the highest file number.

Parameters:

files -

getFiles

public File[] getFiles()

Returns all journal files found in the data directory.

Returns:

all journal files

getFile

public File getFile(int fileNum)

Returns the file corresponding to the specified file number.

Parameters:

fileNum -

shutdown

public void shutdown(long txnId)

Shut down the journal. This will write a checkpoint record to the log, so recovery manager knows the file has been closed in a clean way.

Parameters:

txnId -

setInRecovery

public void setInRecovery(boolean value)

Called to signal that the db is currently in recovery phase, so no output should be written.

Parameters:

value -