simpledb

Class LogFile

java.lang.Object

simpledb.LogFile

public class LogFile
extends java.lang.Object

The format of the log file is as follows:

• The first long integer of the file represents the offset of the last written checkpoint, or -1 if there are no checkpoints
• All additional data in the log consists of log records. Log records are variable length.
• Each log record begins with an integer type and a long integer transaction id.
• Each log record ends with a long integer file offset representing the position in the log file where the record began.
• There are five record types: ABORT, COMMIT, UPDATE, BEGIN, and CHECKPOINT
• ABORT, COMMIT, and BEGIN records contain no additional data
• UPDATE RECORDS consist of two entries, a before image and an after image. These images are serialized Page objects, and can be accessed with the LogFile.readPageData() and LogFile.writePageData() methods. See LogFile.print() for an example.
• CHECKPOINT records consist of active transactions at the time the checkpoint was taken and their first log record on disk. The format of the record is an integer count of the number of transactions, as well as a long integer transaction id and a long integer first record offset for each active transaction.

Field Summary

Fields

Modifier and Type	Field and Description
(package private) static int	ABORT_RECORD
(package private) static int	BEGIN_RECORD
(package private) static int	CHECKPOINT_RECORD
(package private) static int	COMMIT_RECORD
(package private) long	currentOffset
(package private) static int	INT_SIZE
(package private) java.io.File	logFile
(package private) static int	LONG_SIZE
(package private) static long	NO_CHECKPOINT_ID
private java.io.RandomAccessFile	raf
(package private) java.lang.Boolean	recoveryUndecided
(package private) java.util.HashMap<java.lang.Long,java.lang.Long>	tidToFirstLogRecord
(package private) int	totalRecords
(package private) static int	UPDATE_RECORD

Constructor Summary

Constructors

Constructor and Description
LogFile(java.io.File f) Constructor.

Method Summary

Modifier and Type	Method and Description
void	force()
int	getTotalRecords()
void	logAbort(TransactionId tid) Write an abort record to the log for the specified tid, force the log to disk, and perform a rollback
void	logCheckpoint() Checkpoint the log and write a checkpoint record.
void	logCommit(TransactionId tid) Write a commit record to disk for the specified tid, and force the log to disk.
void	logTruncate() Truncate any unneeded portion of the log to reduce its space consumption
void	logWrite(TransactionId tid, Page before, Page after) Write an UPDATE record to disk for the specified tid and page (with provided before and after images.)
void	logXactionBegin(TransactionId tid) Write a BEGIN record for the specified transaction
(package private) void	preAppend()
void	print() Print out a human readable represenation of the log
(package private) Page	readPageData(java.io.RandomAccessFile raf)
void	recover() Recover the database system by ensuring that the updates of committed transactions are installed and that the updates of uncommitted transactions are not installed.
void	rollback(TransactionId tid) Rollback the specified transaction, setting the state of any of pages it updated to their pre-updated state.
void	shutdown() Shutdown the logging system, writing out whatever state is necessary so that start up can happen quickly (without extensive recovery.)
(package private) void	writePageData(java.io.RandomAccessFile raf, Page p)

Methods inherited from class java.lang.Object

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

Field Detail

logFile

final java.io.File logFile

raf

private java.io.RandomAccessFile raf

recoveryUndecided

java.lang.Boolean recoveryUndecided

ABORT_RECORD

static final int ABORT_RECORD

See Also:

Constant Field Values

COMMIT_RECORD

static final int COMMIT_RECORD

See Also:

Constant Field Values

UPDATE_RECORD

static final int UPDATE_RECORD

See Also:

Constant Field Values

BEGIN_RECORD

static final int BEGIN_RECORD

See Also:

Constant Field Values

CHECKPOINT_RECORD

static final int CHECKPOINT_RECORD

See Also:

Constant Field Values

NO_CHECKPOINT_ID

static final long NO_CHECKPOINT_ID

See Also:

Constant Field Values

INT_SIZE

static final int INT_SIZE

See Also:

Constant Field Values

LONG_SIZE

static final int LONG_SIZE

See Also:

Constant Field Values

currentOffset

long currentOffset

totalRecords

int totalRecords

tidToFirstLogRecord

java.util.HashMap<java.lang.Long,java.lang.Long> tidToFirstLogRecord

Constructor Detail

LogFile

public LogFile(java.io.File f)
        throws java.io.IOException

Constructor. Initialize and back the log file with the specified file. We're not sure yet whether the caller is creating a brand new DB, in which case we should ignore the log file, or whether the caller will eventually want to recover (after populating the Catalog). So we make this decision lazily: if someone calls recover(), then do it, while if someone starts adding log file entries, then first throw out the initial log file contents.

Parameters:

f - The log file's name

Throws:

java.io.IOException

Method Detail

preAppend

void preAppend()
        throws java.io.IOException

Throws:

java.io.IOException

getTotalRecords

public int getTotalRecords()

logAbort

public void logAbort(TransactionId tid)
              throws java.io.IOException

Write an abort record to the log for the specified tid, force the log to disk, and perform a rollback

Parameters:

tid - The aborting transaction.

Throws:

java.io.IOException

logCommit

public void logCommit(TransactionId tid)
               throws java.io.IOException

Write a commit record to disk for the specified tid, and force the log to disk.

Parameters:

tid - The committing transaction.

Throws:

java.io.IOException

logWrite

public void logWrite(TransactionId tid,
                     Page before,
                     Page after)
              throws java.io.IOException

Write an UPDATE record to disk for the specified tid and page (with provided before and after images.)

Parameters:

tid - The transaction performing the write

before - The before image of the page

after - The after image of the page

Throws:

java.io.IOException

See Also:

Page.getBeforeImage()

writePageData

void writePageData(java.io.RandomAccessFile raf,
                   Page p)
            throws java.io.IOException

Throws:

java.io.IOException

readPageData

Page readPageData(java.io.RandomAccessFile raf)
           throws java.io.IOException

Throws:

java.io.IOException

logXactionBegin

public void logXactionBegin(TransactionId tid)
                     throws java.io.IOException

Write a BEGIN record for the specified transaction

Parameters:

tid - The transaction that is beginning

Throws:

java.io.IOException

logCheckpoint

public void logCheckpoint()
                   throws java.io.IOException

Checkpoint the log and write a checkpoint record.

Throws:

java.io.IOException

logTruncate

public void logTruncate()
                 throws java.io.IOException

Truncate any unneeded portion of the log to reduce its space consumption

Throws:

java.io.IOException

rollback

public void rollback(TransactionId tid)
              throws java.util.NoSuchElementException,
                     java.io.IOException

Rollback the specified transaction, setting the state of any of pages it updated to their pre-updated state. To preserve transaction semantics, this should not be called on transactions that have already committed (though this may not be enforced by this method.)

Parameters:

tid - The transaction to rollback

Throws:

java.util.NoSuchElementException

java.io.IOException

shutdown

public void shutdown()

Shutdown the logging system, writing out whatever state is necessary so that start up can happen quickly (without extensive recovery.)

recover

public void recover()
             throws java.io.IOException

Recover the database system by ensuring that the updates of committed transactions are installed and that the updates of uncommitted transactions are not installed.

Throws:

java.io.IOException

print

public void print()
           throws java.io.IOException

Print out a human readable represenation of the log

Throws:

java.io.IOException

force

public void force()
           throws java.io.IOException

Throws:

java.io.IOException