This class is a simple implementation of a reliable Log. The client of a ReliableLog must provide a set of callbacks (via a LogHandler) that enables a ReliableLog to read and write checkpoints and log records. This implementation ensures that the current value of the data stored (via a ReliableLog) is recoverable after a system crash.

The secondary storage strategy is to record values in files using a representation of the caller's choosing. Two sorts of files are kept: snapshots and logs. At any instant, one snapshot is current. The log consists of a sequence of updates that have occurred since the current snapshot was taken. The current stable state is the value of the snapshot, as modified by the sequence of updates in the log. From time to time, the client of a ReliableLog instructs the package to make a new snapshot and clear the log. A ReliableLog arranges disk writes such that updates are stable (as long as the changes are force-written to disk) and atomic : no update is lost, and each update either is recorded completely in the log or not at all. Making a new snapshot is also atomic.

Normal use for maintaining the recoverable store is as follows: The client maintains the relevant data structure in virtual memory. As updates happen to the structure, the client informs the ReliableLog (all it "log") by calling log.update. Periodically, the client calls log.snapshot to provide the current value of the data structure. On restart, the client calls log.recover to obtain the latest snapshot and the following sequences of updates; the client applies the updates to the snapshot to obtain the state that existed before the crash.

The current logfile format is:

a format version number (two 4-octet integers, major and minor), followed by
a sequence of log records. Each log record contains, in order,
1. a 4-octet integer representing the length of the following log data,
2. the log data (variable length).

Nested and Inner Type Summary

Modifier and Type	Class and Description
public static class	ReliableLog.LogFile ReliableLog's log file implementation.

Field Summary

Modifier and Type	Field and Description
private boolean	Debug
private File	dir
private static long	diskPageSize
private LogHandler	handler
private final byte[]	intBuf
private static int	intBytes
private long	lastLog
private long	lastSnapshot
private ReliableLog.LogFile	log
private long	logBytes
private static final Constructor<? extends ReliableLog.LogFile>	logClassConstructor Constructor for the log file.
private int	logEntries
private static String	logfilePrefix
private String	logName
private int	majorFormatVersion
private int	minorFormatVersion
private static String	newVersionFile
public static final int	PreferredMajorVersion
public static final int	PreferredMinorVersion
private long	snapshotBytes
private static String	snapshotPrefix
private int	version
private static String	versionFile

Constructor Summary

Access	Constructor and Description
public	ReliableLog(String path to the stable storage directory dirPath, LogHandler the closure object containing callbacks for logging and recovery handler, boolean ignored pad) Creates a ReliableLog to handle checkpoints and logging in a stable storage directory.
public	ReliableLog(String path to the stable storage directory dirPath, LogHandler the closure object containing callbacks for logging and recovery handler) Creates a ReliableLog to handle checkpoints and logging in a stable storage directory.

Method Summary

Modifier and Type	Method and Description
public synchronized void	close() Close the stable storage directory in an orderly manner.
private void	commitToNewVersion() Commits (atomically) the new version.
private void	createFirstVersion() Creates the initial version file
private void	deleteFile(String the name of the file name) Delete a file.
private void	deleteLogFile(int the version to remove ver) Removes the log file.
private void	deleteNewVersionFile() Removes the new version number file.
private void	deleteSnapshot(int the version to remove ver) Removes the snapshot file.
private String	fName(String the leaf name of the file name) Generates a filename prepended with the stable storage directory path.
private static Constructor<? extends ReliableLog.LogFile>	getLogClassConstructor() Returns the constructor for the log file if the system property sun.rmi.log.class is non-null and the class specified by the property a) can be loaded, b) is a subclass of LogFile, and c) has a public two-arg constructor (String, String); otherwise returns null.
private void	getVersion() Sets the version.
private void	incrVersion() Increments the directory version number.
private void	initializeLogFile() Creates a new log file, truncated and initialized with the format version number preferred by this implementation.
public long	logSize() Returns the size of the log file in bytes;
private void	openLogFile(boolean if true and file exists, file is truncated to zero length truncate) Opens the log file in read/write mode.
private int	Returns: the version readVersion(String the name of the version file name) Reads version number from a file.
public synchronized Object	recover() Returns an object which is the value recorded in the current snapshot.
private Object	Returns: the resulting state of the object after all updates recoverUpdates(Object the most recent snapshot state) Applies outstanding updates to the snapshot.
public synchronized void	snapshot(Object the object representing the new snapshot value) Records this value as the current snapshot by invoking the client supplied "snapshot" callback and then empties the log.
public long	snapshotSize() Returns the size of the snapshot file in bytes;
public synchronized void	update(Object the object representing the update value) Records this update in the log file (does not force update to disk).
public synchronized void	update(Object the object representing the update value, boolean ignored; changes are always forced to disk forceToDisk) Records this update in the log file.
private String	versionName(String version file name name) Generates a version 0 filename prepended with the stable storage directory path
private String	versionName(String prefix, int a version number ver) Generates a version filename prepended with the stable storage directory path with the version number as a suffix.
private void	writeInt(DataOutput output stream out, int int value val) Write an int value in single write operation.
private void	writeVersionFile(boolean if true, writes to a new version file newVersion) Writes out version number to file.

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll toString wait wait wait

Field Detail

Debug	back to summary
private boolean Debug

dir	back to summary
private File dir

diskPageSize	back to summary
private static long diskPageSize

handler	back to summary
private LogHandler handler

intBuf	back to summary
private final byte[] intBuf

intBytes	back to summary
private static int intBytes

lastLog	back to summary
private long lastLog

lastSnapshot	back to summary
private long lastSnapshot

log	back to summary
private ReliableLog.LogFile log

logBytes	back to summary
private long logBytes

logClassConstructor	back to summary
private static final Constructor<? extends ReliableLog.LogFile> logClassConstructor Constructor for the log file. If the system property sun.rmi.log.class is non-null and the class specified by this property a) can be loaded, b) is a subclass of LogFile, and c) has a public two-arg constructor (String, String), ReliableLog uses the constructor to construct the LogFile.

logEntries	back to summary
private int logEntries

logfilePrefix	back to summary
private static String logfilePrefix

logName	back to summary
private String logName

majorFormatVersion	back to summary
private int majorFormatVersion

minorFormatVersion	back to summary
private int minorFormatVersion

newVersionFile	back to summary
private static String newVersionFile

PreferredMajorVersion	back to summary
public static final int PreferredMajorVersion

PreferredMinorVersion	back to summary
public static final int PreferredMinorVersion

snapshotBytes	back to summary
private long snapshotBytes

snapshotPrefix	back to summary
private static String snapshotPrefix

version	back to summary
private int version

versionFile	back to summary
private static String versionFile

Constructor Detail

ReliableLog	back to summary
public ReliableLog(String dirPath, LogHandler handler, boolean pad) throws IOException Creates a ReliableLog to handle checkpoints and logging in a stable storage directory. Parameters dirPath:String path to the stable storage directory handler:LogHandler the closure object containing callbacks for logging and recovery pad:boolean ignored Exceptions IOException: If a directory creation error has occurred or if initialSnapshot callback raises an exception or if an exception occurs during invocation of the handler's snapshot method or if other IOException occurs.

ReliableLog

Modifier and Type	Method and Description
protected boolean	checkSpansBoundary(long fp) Returns true if writing 4 bytes starting at the specified file position, would span a 512 byte sector boundary; otherwise returns false.
protected void	sync() Invokes sync on the file descriptor for this log file.

public Class ReliableLog

Nested and Inner Type Summary

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail

public Class ReliableLog.LogFile

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail