com.bigdata.ha.halog

Class HALogWriter

java.lang.Object

com.bigdata.ha.halog.HALogWriter

All Implemented Interfaces:

IHALogWriter

public class HALogWriter
extends Object
implements IHALogWriter

Wrapper class to handle process log creation and output for HA.

The process log stores the HAWriteMessage and buffers to support reading and reprocessing as part of the HA synchronization protocol.

The writer encapsulates not only the writing of individual messages but also the closing and creation of new files.

Author:

Martyn Cutcher

Field Summary

Fields

Modifier and Type	Field and Description
static int	MAGIC Magic value for HA Log (the root blocks have their own magic value).
static int	VERSION1 HA log version number (version 1).

Constructor Summary

Constructors

Constructor and Description
HALogWriter(File logDir, boolean doubleSync)

Method Summary

Methods

Modifier and Type	Method and Description
void	closeHALog(IRootBlockView rootBlock) Write the final root block on the HA log and close the file.
void	createLog(IRootBlockView rootBlock) Open an HA log file for the write set starting with the given root block.
void	disableHALog() Disable (and remove) the current log file if one is open (an HALog file which has been committed by applying its closing root block is NOT removed).
long	getCommitCounter() Return the commit counter that is expected for the writes that will be logged (the same commit counter that is on the opening root block).
File	getFile() Return the log file (if any).
static File	getHALogFileName(File dir, long commitCounter) Return the HALog file associated with the commit counter.
IHALogReader	getReader(long commitCounter) Return the IHALogReader for the specified commit counter.
long	getSequence() Return the sequence number that is expected for the next write.
boolean	isHALogOpen() Return true iff there is an HALog file that is currently open for writing.
String	toString()
void	writeOnHALog(IHAWriteMessage msg, ByteBuffer data) Write the message and the data on the live HALog.

Methods inherited from class java.lang.Object

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

Field Detail

MAGIC

public static final int MAGIC

Magic value for HA Log (the root blocks have their own magic value).

See Also:

Constant Field Values

VERSION1

public static final int VERSION1

HA log version number (version 1).

See Also:

Constant Field Values

Constructor Detail

HALogWriter

public HALogWriter(File logDir,
           boolean doubleSync)

Parameters:

logDir - The directory in which the HALog files reside.

doubleSync - When true, the HALog is flushed to the disk before the closing root block is written and then once again after the closing root block is written. When false, the HALog is flushed only once, after the closing root block is written.

See Also:

Longevity and stress test protocol for HA QA , HAJournalServer can not restart due to logically empty log file

Method Detail

getCommitCounter

public long getCommitCounter()

Description copied from interface: IHALogWriter

Return the commit counter that is expected for the writes that will be logged (the same commit counter that is on the opening root block).

Note: Once the HALog is sealed, the closing root block will have a commitCounter that is equal to getCommitCounter() + 1.

Note: The HALog filename contains the closing commit counter - that is, the HALog file is named for the commit counter associated with the closing root block for a given write set.

Specified by:

getCommitCounter in interface IHALogWriter

getSequence

public long getSequence()

Description copied from interface: IHALogWriter

Return the sequence number that is expected for the next write.

Specified by:

getSequence in interface IHALogWriter

isHALogOpen

public boolean isHALogOpen()

Description copied from interface: IHALogWriter

Return true iff there is an HALog file that is currently open for writing.

Specified by:

isHALogOpen in interface IHALogWriter

getFile

public File getFile()

Return the log file (if any).

getHALogFileName

public static File getHALogFileName(File dir,
                    long commitCounter)

Return the HALog file associated with the commit counter.

Parameters:

dir - The HALog directory.

commitCounter - The closing commit counter (the HALog file is named for the commit counter that will be associated with the closing root block).

Returns:

The HALog File.

toString

public String toString()

Overrides:

toString in class Object

createLog

public void createLog(IRootBlockView rootBlock)
               throws FileNotFoundException,
                      IOException

Open an HA log file for the write set starting with the given root block.

Parameters:

rootBlock - The root block.

Throws:

FileNotFoundException

IOException

closeHALog

public void closeHALog(IRootBlockView rootBlock)
                throws FileNotFoundException,
                       IOException

Write the final root block on the HA log and close the file. This "seals" the file, which now represents the entire write set associated with the commit point in the given root block.

Specified by:

closeHALog in interface IHALogWriter

Parameters:

rootBlock - The final root block for the write set.

Throws:

IOException

FileNotFoundException

writeOnHALog

public void writeOnHALog(IHAWriteMessage msg,
                ByteBuffer data)
                  throws IOException,
                         IllegalStateException

Write the message and the data on the live HALog.

Specified by:

writeOnHALog in interface IHALogWriter

Parameters:

msg - The message.

data - The data.

Throws:

IllegalStateException - if the message is not appropriate for the state of the log.

IOException - if we can not write on the log.

disableHALog

public void disableHALog()
                  throws IOException

Description copied from interface: IHALogWriter

Disable (and remove) the current log file if one is open (an HALog file which has been committed by applying its closing root block is NOT removed).

Specified by:

disableHALog in interface IHALogWriter

Throws:

IOException

See Also:

HAJournalServer reports "follower" but is in SeekConsensus and is not participating in commits

getReader

public IHALogReader getReader(long commitCounter)
                       throws FileNotFoundException,
                              IOException

Return the IHALogReader for the specified commit counter. If the request identifies the HALog that is currently being written, then an IHALogReader will be returned that will "see" newly written entries on the HALog. If the request identifies a historical HALog that has been closed and which exists, then a reader will be returned for that HALog file. Otherwise, an exception is thrown.

Parameters:

commitCounter - The commit counter associated with the commit point at the close of the write set (the commit counter that is in the file name).

Returns:

The IHALogReader.

Throws:

IOException - if the commitCounter identifies an HALog file that does not exist or can not be read.

FileNotFoundException