org.apache.derby.impl.store.replication.buffer

Class ReplicationLogBuffer

java.lang.Object

org.apache.derby.impl.store.replication.buffer.ReplicationLogBuffer

public class ReplicationLogBuffer
extends java.lang.Object

Used for the replication master role only. When a Derby instance has the replication master role for a database 'x', all log records that are written to the local log file are also appended to this log buffer. The replication master service will consume chunks of log from this buffer and send it to the Derby instance with the slave role for 'x'. ReplicationLogBuffer consists of a number of LogBufferElements. Elements that are not in use are in the freeBuffers list, while elements that contains dirty log are in dirtyBuffers. Chunks of log records are appended to the buffer element in currentDirtyBuffer. Hence, the life cycle of buffer elements is: freeBuffers -> currentDirtyBuffer -> dirtyBuffers -> freeBuffers To append chunks of log records to the buffer, use appendLog(...) To consume chunks of log records, use next() followed by getData(), getLastInstant() and getSize(). These get-methods throw NoSuchElementException if next() returned false, meaning that there were no dirty log at the time next() was called. Threads: ReplicationLogBuffer is threadsafe. It can be used by a logger (LogToFile) and a log consumer (LogShipping service) concurrently without further synchronization. Important: If methods in this class calls methods outside this package (e.g. MasterFactory#workToDo), make sure that deadlocks are not introduced. If possible, a call to any method in another package should be done without holding latches in this class.

Field Summary

Fields

Modifier and Type	Field and Description
private LogBufferElement	currentDirtyBuffer
static int	DEFAULT_NUMBER_LOG_BUFFERS
private int	defaultBufferSize
private java.util.LinkedList	dirtyBuffers
private java.util.LinkedList	freeBuffers
private java.lang.Object	listLatch
private MasterFactory	mf
private byte[]	outBufferData
private long	outBufferLastInstant
private int	outBufferStored
private java.lang.Object	outputLatch
private boolean	validOutBuffer

Constructor Summary

Constructors

Constructor and Description
ReplicationLogBuffer(int bufferSize, MasterFactory mf) Class constructor specifies the number of buffer elements and the master controller that creates this replication log buffer.

Method Summary

Modifier and Type	Method and Description
void	appendLog(long greatestInstant, byte[] log, int logOffset, int logLength) Append a chunk of log records to the log buffer.
byte[]	getData() Returns a byte[] containing a chunk of serialized log records.
int	getFillInformation() Used to calculate the Fill Information.
long	getLastInstant() Can be used so that only the necessary log records are sent when a flush(LogInstant flush_to_this) is called in the log factory.
int	getSize()
boolean	next() Sets the output data to that of the next (oldest) buffer element in dirtyBuffers so that getData(), getLastInstant() and getSize() return values from the next oldest chunk of log.
private void	switchDirtyBuffer() Appends the currentDirtyBuffer to dirtyBuffers, and makes a fresh buffer element from freeBuffers the currentDirtyBuffer.
boolean	validData() Method to determine whether or not the buffer had any log records the last time next() was called.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_NUMBER_LOG_BUFFERS

public static final int DEFAULT_NUMBER_LOG_BUFFERS

See Also:

Constant Field Values

dirtyBuffers

private final java.util.LinkedList dirtyBuffers

freeBuffers

private final java.util.LinkedList freeBuffers

currentDirtyBuffer

private LogBufferElement currentDirtyBuffer

validOutBuffer

private boolean validOutBuffer

outBufferData

private byte[] outBufferData

outBufferStored

private int outBufferStored

outBufferLastInstant

private long outBufferLastInstant

listLatch

private final java.lang.Object listLatch

outputLatch

private final java.lang.Object outputLatch

defaultBufferSize

private int defaultBufferSize

mf

private final MasterFactory mf

Constructor Detail

ReplicationLogBuffer

public ReplicationLogBuffer(int bufferSize,
                            MasterFactory mf)

Class constructor specifies the number of buffer elements and the master controller that creates this replication log buffer.

Parameters:

bufferSize - the default number of buffer elements

mf - Used to notify the master controller that a log buffer element is full and work needs to be done.

Method Detail

appendLog

public void appendLog(long greatestInstant,
                      byte[] log,
                      int logOffset,
                      int logLength)
               throws LogBufferFullException

Append a chunk of log records to the log buffer.

Parameters:

greatestInstant - the instant of the log record that was added last to this chunk of log

log - the chunk of log records

logOffset - offset in log to start copy from

logLength - number of bytes to copy, starting from logOffset

Throws:

LogBufferFullException - - thrown if there is not enough free space in the buffer to store the chunk of log.

next

public boolean next()

Sets the output data to that of the next (oldest) buffer element in dirtyBuffers so that getData(), getLastInstant() and getSize() return values from the next oldest chunk of log. Used by the log consumer (the LogShipping service) to move to the next chunk of log in the buffer.

Returns:

true if there is log in the buffer, resulting in valid data for the get-methods

getData

public byte[] getData()
               throws java.util.NoSuchElementException

Returns a byte[] containing a chunk of serialized log records. Always returns the log that was oldest at the time next() was called last time. Use next() to move to the next chunk of log records.

Returns:

A copy of the current byte[], which is a chunk of log

Throws:

java.util.NoSuchElementException - if there was no log in the buffer the last time next() was called.

validData

public boolean validData()

Method to determine whether or not the buffer had any log records the last time next() was called.

Returns:

true if the buffer contained log records the last time next() was called. False if not, or if next() has not been called yet.

getSize

public int getSize()
            throws java.util.NoSuchElementException

Returns:

The number of bytes returned by getData

Throws:

java.util.NoSuchElementException - if there was no log in the buffer the last time next() was called.

getLastInstant

public long getLastInstant()
                    throws java.util.NoSuchElementException

Can be used so that only the necessary log records are sent when a flush(LogInstant flush_to_this) is called in the log factory. Returns the highest log instant in the chunk of log that can be read with getData().

Returns:

The highest log instant in the chunk of log returned by getData().

Throws:

java.util.NoSuchElementException - if there was no log in the buffer the last time next() was called.

switchDirtyBuffer

private void switchDirtyBuffer()
                        throws LogBufferFullException

Appends the currentDirtyBuffer to dirtyBuffers, and makes a fresh buffer element from freeBuffers the currentDirtyBuffer. Note: this method is not synchronized since all uses of it is inside synchronized(listLatch) code blocks.

Throws:

LogBufferFullException - if the freeBuffers list is empty

getFillInformation

public int getFillInformation()

Used to calculate the Fill Information. The fill information is a indicator of how full the buffer is at any point of time fill information = (full buffers/Total Buffers)*100. The Fill information ranges between 0-100 (both 0 and 100 inclusive).

Returns:

an integer value between 0-100 representing the fill information.