Apache Derby Database Engine and Embedded JDBC Driver 10.17.1.0 · org.apache.derby.impl.store.replication.buffer.ReplicationLogBuffer

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

Modifier and Type	Field and Description
private LogBufferElement	currentDirtyBuffer
public static final int	DEFAULT_NUMBER_LOG_BUFFERS
private int	defaultBufferSize
private final LinkedList<LogBufferElement>	dirtyBuffers
private final LinkedList<LogBufferElement>	freeBuffers
private final Object	listLatch
private final MasterFactory	mf
private byte[]	outBufferData
private long	outBufferLastInstant
private int	outBufferStored
private final Object	outputLatch
private boolean	validOutBuffer

Constructor Summary

Access	Constructor and Description
public	ReplicationLogBuffer(int the default number of buffer elements bufferSize, MasterFactory Used to notify the master controller that a log buffer element is full and work needs to be done. 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
public void	appendLog(long the instant of the log record that was added last to this chunk of log greatestInstant, byte[] the chunk of log records log, int offset in log to start copy from logOffset, int number of bytes to copy, starting from logOffset logLength) Append a chunk of log records to the log buffer.
public byte[]	Returns: A copy of the current byte[], which is a chunk of log getData() Returns a byte[] containing a chunk of serialized log records.
public int	Returns: an integer value between 0-100 representing the fill information. getFillInformation() Used to calculate the Fill Information.
public long	Returns: The highest log instant in the chunk of log returned by getData(). 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.
public int	Returns: The number of bytes returned by getData getSize()
public boolean	Returns: true if there is log in the buffer, resulting in valid data for the get-methods 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.
public boolean	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. validData() Method to determine whether or not the buffer had any log records the last time next() was called.

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

Field Detail

currentDirtyBuffer	back to summary
private LogBufferElement currentDirtyBuffer

DEFAULT_NUMBER_LOG_BUFFERS	back to summary
public static final int DEFAULT_NUMBER_LOG_BUFFERS

defaultBufferSize	back to summary
private int defaultBufferSize

dirtyBuffers	back to summary
private final LinkedList<LogBufferElement> dirtyBuffers

freeBuffers	back to summary
private final LinkedList<LogBufferElement> freeBuffers

listLatch	back to summary
private final Object listLatch

mf	back to summary
private final MasterFactory mf

outBufferData	back to summary
private byte[] outBufferData

outBufferLastInstant	back to summary
private long outBufferLastInstant

outBufferStored	back to summary
private int outBufferStored

outputLatch	back to summary
private final Object outputLatch

validOutBuffer	back to summary
private boolean validOutBuffer

Constructor Detail

ReplicationLogBuffer	back to summary
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:int the default number of buffer elements mf:MasterFactory Used to notify the master controller that a log buffer element is full and work needs to be done.

ReplicationLogBuffer

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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:int: the default number of buffer elements
mf:MasterFactory: Used to notify the master controller that a log buffer element is full and work needs to be done.

Method Detail

appendLog	back to summary
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:long the instant of the log record that was added last to this chunk of log log:byte[] the chunk of log records logOffset:int offset in log to start copy from logLength:int number of bytes to copy, starting from logOffset Exceptions LogBufferFullException: - thrown if there is not enough free space in the buffer to store the chunk of log.

appendLog

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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:long: the instant of the log record that was added last to this chunk of log
log:byte[]: the chunk of log records
logOffset:int: offset in log to start copy from
logLength:int: number of bytes to copy, starting from logOffset

Exceptions

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

getData	back to summary
public byte[] getData() throws 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:byte[] A copy of the current byte[], which is a chunk of log Exceptions NoSuchElementException: if there was no log in the buffer the last time next() was called.

getData

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public byte[] getData() throws 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:byte[]

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

Exceptions

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

getFillInformation	back to summary
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:int an integer value between 0-100 representing the fill information.

getFillInformation

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

getLastInstant	back to summary
public long getLastInstant() throws 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:long The highest log instant in the chunk of log returned by getData(). Exceptions NoSuchElementException: if there was no log in the buffer the last time next() was called.

getLastInstant

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public long getLastInstant() throws 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:long

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

Exceptions

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

getSize	back to summary
public int getSize() throws NoSuchElementException Returns:int The number of bytes returned by getData Exceptions NoSuchElementException: if there was no log in the buffer the last time next() was called.

next	back to summary
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:boolean true if there is log in the buffer, resulting in valid data for the get-methods

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

switchDirtyBuffer	back to summary
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. Exceptions LogBufferFullException: if the freeBuffers list is empty

switchDirtyBuffer

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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.

Exceptions

LogBufferFullException:: if the freeBuffers list is empty

validData	back to summary
public boolean validData() Method to determine whether or not the buffer had any log records the last time next() was called. Returns:boolean true if the buffer contained log records the last time next() was called. False if not, or if next() has not been called yet.

validData

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public boolean validData()

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

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

public Class ReplicationLogBuffer

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Field Detail

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Method Detail