org.codehaus.activemq.journal.impl
Class JournalImpl

java.lang.Object
  org.codehaus.activemq.journal.impl.JournalImpl

All Implemented Interfaces:

Journal

public class JournalImpl

extends Object

implements Journal

A high speed Journal implementation. Inspired by the ideas of the Howl project but tailored to the needs of ActiveMQ.

This Journal provides the following features:

• Conncurrent writes are batched into a single write/force done by a background thread.
• Uses preallocated logs to avoid disk fragmentation and performance degregation.
• The number and size of the preallocated logs are configurable.
• Uses direct ByteBuffers to write data to log files.
• Allows logs to grow in case of an overflow condition so that overflow exceptions are not not thrown. Grown logs that are inactivated (due to a new mark) are resized to thier original size.
• No limit on the size of the record written to the journal
• Should be possible to extend so that multiple physical disk are used concurrently to increase throughput and decrease latency.

This class is a thing wrapper around a LogFileManager. It may be possible to extends this class so that it manages multiple LogFileManager objects to allow logging to multiple physical disks.

Version:

$Revision: 1.3 $

Field Summary

(package private) LogFileManager	manager
(package private) LongSequenceGenerator	sequenceGenerator

Constructor Summary

JournalImpl()

JournalImpl(File logDirectory)

JournalImpl(File logDirectory, int segments, int segmentSize)

Method Summary

void	close() Close the Journal.
RecordLocation	getMark() Obtains the mark that was set in the Journal.
RecordLocation	getNextRecordLocation(RecordLocation lastLocation) Allows you to get the next RecordLocation after the location that is in the journal.
byte[]	read(RecordLocation location) Reads a previously written record from the journal.
void	setJournalEventListener(JournalEventListener eventListener) Registers a JournalEventListener that will receive notifications from the Journal.
void	setMark(RecordLocation recordLocator, boolean force) Informs the journal that all the journal space up to the location is no longer needed and can be reclaimed for reuse.
String	toString()
RecordLocation	write(byte[] data, boolean sync) Writes a byte array record to the journal.

Methods inherited from class java.lang.Object

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

Field Detail

manager

LogFileManager manager

sequenceGenerator

LongSequenceGenerator sequenceGenerator

Constructor Detail

JournalImpl

public JournalImpl()
            throws IOException

JournalImpl

public JournalImpl(File logDirectory)
            throws IOException

JournalImpl

public JournalImpl(File logDirectory,
                   int segments,
                   int segmentSize)
            throws IOException

Method Detail

write

public RecordLocation write(byte[] data,
                            boolean sync)
                     throws IOException

Description copied from interface: Journal

Writes a byte array record to the journal. If sync is true, then this call blocks until the data has landed on the physical disk. Otherwise, this call returns imeadiatly.

Specified by:

write in interface Journal

Parameters:

data - - the data to be written to disk.

sync - - If this call should block until the data lands on disk.

Returns:

RecordLocation the location where the data will be written to on disk.

Throws:

IOException

See Also:

Journal.write(byte[], boolean)

setMark

public void setMark(RecordLocation recordLocator,
                    boolean force)
             throws InvalidRecordLocationException,
                    IOException

Description copied from interface: Journal

Informs the journal that all the journal space up to the location is no longer needed and can be reclaimed for reuse.

Specified by:

setMark in interface Journal

Parameters:

recordLocator - the location of the record to mark. All record locations before the marked location will no longger be vaild.

force - if this call should block until the mark is set on the journal.

Throws:

InvalidRecordLocationException - if location parameter is out of range. It cannot be a location that is before the current mark.

IOException - if the record could not be read.

See Also:

Journal.setMark(org.codehaus.activemq.journal.RecordLocation, boolean)

getMark

public RecordLocation getMark()

Description copied from interface: Journal

Obtains the mark that was set in the Journal.

Specified by:

getMark in interface Journal

Returns:

the mark that was set in the Journal.

See Also:

Journal.getMark()

close

public void close()
           throws IOException

Description copied from interface: Journal

Close the Journal. This is blocking operation that waits for any pending put opperations to be forced to disk. Once the Journal is closed, all other methods of the journal should throw IllegalStateException.

Specified by:

close in interface Journal

Throws:

IOException - if an error occurs while the journal is being closed.

See Also:

Journal.close()

setJournalEventListener

public void setJournalEventListener(JournalEventListener eventListener)

Description copied from interface: Journal

Registers a JournalEventListener that will receive notifications from the Journal.

Specified by:

setJournalEventListener in interface Journal

Parameters:

eventListener - object that will receive journal events.

See Also:

Journal.setJournalEventListener(org.codehaus.activemq.journal.JournalEventListener)

getNextRecordLocation

public RecordLocation getNextRecordLocation(RecordLocation lastLocation)
                                     throws IOException,
                                            InvalidRecordLocationException

Description copied from interface: Journal

Allows you to get the next RecordLocation after the location that is in the journal.

Specified by:

getNextRecordLocation in interface Journal

Parameters:

lastLocation - the reference location the is used to find the next location. To get the oldest location available in the journal, location should be set to null.

Returns:

the next record location

Throws:

InvalidRecordLocationException

IOException

See Also:

Journal.getNextRecordLocation(org.codehaus.activemq.journal.RecordLocation)

read

public byte[] read(RecordLocation location)
            throws InvalidRecordLocationException,
                   IOException

Description copied from interface: Journal

Reads a previously written record from the journal.

Specified by:

read in interface Journal

Parameters:

location - is where to read the record from.

Returns:

the data previously written at the location.

Throws:

IOException - if the record could not be read.

InvalidRecordLocationException - if location parameter is out of range. It cannot be a location that is before the current mark.

See Also:

Journal.getNextRecordLocation(org.codehaus.activemq.journal.RecordLocation)

toString

public String toString()

See Also:

Object.toString()