Class ReplicationLogBuffer
- java.lang.Object
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- org.apache.derby.impl.store.replication.buffer.ReplicationLogBuffer
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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.
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Field Summary
Fields Modifier and Type Field Description private LogBufferElement
currentDirtyBuffer
static int
DEFAULT_NUMBER_LOG_BUFFERS
private int
defaultBufferSize
private java.util.LinkedList<LogBufferElement>
dirtyBuffers
private java.util.LinkedList<LogBufferElement>
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
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Constructor Summary
Constructors Constructor Description ReplicationLogBuffer(int bufferSize, MasterFactory mf)
Class constructor specifies the number of buffer elements and the master controller that creates this replication log buffer.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method 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.
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Field Detail
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DEFAULT_NUMBER_LOG_BUFFERS
public static final int DEFAULT_NUMBER_LOG_BUFFERS
- See Also:
- Constant Field Values
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dirtyBuffers
private final java.util.LinkedList<LogBufferElement> dirtyBuffers
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freeBuffers
private final java.util.LinkedList<LogBufferElement> freeBuffers
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currentDirtyBuffer
private LogBufferElement currentDirtyBuffer
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validOutBuffer
private boolean validOutBuffer
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outBufferData
private byte[] outBufferData
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outBufferStored
private int outBufferStored
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outBufferLastInstant
private long outBufferLastInstant
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listLatch
private final java.lang.Object listLatch
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outputLatch
private final java.lang.Object outputLatch
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defaultBufferSize
private int defaultBufferSize
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mf
private final MasterFactory mf
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Constructor Detail
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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 elementsmf
- Used to notify the master controller that a log buffer element is full and work needs to be done.
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Method Detail
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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 loglog
- the chunk of log recordslogOffset
- offset in log to start copy fromlogLength
- 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.
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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
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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.
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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.
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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.
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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.
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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
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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.
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