org.apache.derby.impl.store.replication.master

Class AsynchronousLogShipper

java.lang.Object

java.lang.Thread

org.apache.derby.impl.store.replication.master.AsynchronousLogShipper

All Implemented Interfaces:

java.lang.Runnable

public class AsynchronousLogShipper
extends java.lang.Thread

Does asynchronous shipping of log records from the master to the slave being replicated to. The implementation does not ship log records as soon as they become available in the log buffer (synchronously), instead it does log shipping in the following two-fold scenarios 1) Periodically (i.e.) at regular intervals of time. 2) when a request is sent from the master controller (force flushing of the log buffer). 3) when a notification is received from the log shipper about a log buffer element becoming full and the load on the log buffer so warrants a ship.

Nested Class Summary

Nested classes/interfaces inherited from class java.lang.Thread

java.lang.Thread.State, java.lang.Thread.UncaughtExceptionHandler

Field Summary

Fields

Modifier and Type	Field and Description
static int	DEFAULT_FORCEFLUSH_TIMEOUT The number of millis a call to forceFlush will wait before giving up sending a chunk of log to the slave

Fields inherited from class java.lang.Thread

MAX_PRIORITY, MIN_PRIORITY, NORM_PRIORITY

Constructor Summary

Constructors

Constructor and Description
AsynchronousLogShipper(ReplicationLogBuffer logBuffer, ReplicationMessageTransmit transmitter, MasterController masterController, ReplicationLogger repLogger) Constructor initializes the log buffer, the replication message transmitter, the shipping interval and the master controller.

Method Summary

Modifier and Type	Method and Description
void	flushBuffer() Transmits all the log records in the log buffer to the slave.
void	flushedInstance(long latestInstanceFlushedToDisk) updates the information about the latest instance of the log record that has been flushed to the disk.
void	forceFlush() Transmits a chunk of log record from the log buffer to the slave, used by the master controller when the log buffer is full and some space needs to be freed for further log records.
long	getHighestShippedInstant() Get the highest log instant shipped so far
void	run() Ships log records from the log buffer to the slave being replicated to.
void	stopLogShipment() Stop shipping log records.
void	workToDo() Used to notify the log shipper that a log buffer element is full.

Methods inherited from class java.lang.Thread

activeCount, checkAccess, countStackFrames, currentThread, destroy, dumpStack, enumerate, getAllStackTraces, getContextClassLoader, getDefaultUncaughtExceptionHandler, getId, getName, getPriority, getStackTrace, getState, getThreadGroup, getUncaughtExceptionHandler, holdsLock, interrupt, interrupted, isAlive, isDaemon, isInterrupted, join, join, join, resume, setContextClassLoader, setDaemon, setDefaultUncaughtExceptionHandler, setName, setPriority, setUncaughtExceptionHandler, sleep, sleep, start, stop, stop, suspend, toString, yield

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

DEFAULT_FORCEFLUSH_TIMEOUT

public static final int DEFAULT_FORCEFLUSH_TIMEOUT

The number of millis a call to forceFlush will wait before giving up sending a chunk of log to the slave

See Also:

Constant Field Values

Constructor Detail

AsynchronousLogShipper

public AsynchronousLogShipper(ReplicationLogBuffer logBuffer,
                              ReplicationMessageTransmit transmitter,
                              MasterController masterController,
                              ReplicationLogger repLogger)

Constructor initializes the log buffer, the replication message transmitter, the shipping interval and the master controller.

Parameters:

logBuffer - the replication log buffer that contains the log record chunks to be transmitted to the slave.

transmitter - the replication message transmitter that is used for network transmission of retrieved log records.

masterController - The master controller that initialized this log shipper.

repLogger - The replication logger that will write messages to the log file (typically derby.log)

Method Detail

run

public void run()

Ships log records from the log buffer to the slave being replicated to. The log shipping happens between shipping intervals of time, the shipping interval being derived from the fill information (an indicator of load in the log buffer) obtained from the log buffer. The shipping can also be triggered in the following situations, 1) Based on notifications from the log buffer, where the fill information is again used as the basis to decide whether a shipping should happen or not 2) On a forceFlush triggered by the log buffer becoming full and the LogBufferFullException being thrown.

Specified by:

run in interface java.lang.Runnable

Overrides:

run in class java.lang.Thread

flushBuffer

public void flushBuffer()
                 throws java.io.IOException,
                        StandardException

Transmits all the log records in the log buffer to the slave.

Throws:

java.io.IOException - If an exception occurs while trying to ship the replication message (containing the log records) across the network.

StandardException - If an exception occurs while trying to read log records from the log buffer.

forceFlush

public void forceFlush()
                throws java.io.IOException,
                       StandardException

Transmits a chunk of log record from the log buffer to the slave, used by the master controller when the log buffer is full and some space needs to be freed for further log records.

Throws:

java.io.IOException - If an exception occurs while trying to ship the replication message (containing the log records) across the network.

StandardException - If an exception occurs while trying to read log records from the log buffer.

getHighestShippedInstant

public long getHighestShippedInstant()

Get the highest log instant shipped so far

Returns:

the highest log instant shipped so far

flushedInstance

public void flushedInstance(long latestInstanceFlushedToDisk)

updates the information about the latest instance of the log record that has been flushed to the disk. Calling this method has no effect in this asynchronous implementation of the log shipper.

Parameters:

latestInstanceFlushedToDisk - a long that contains the latest instance of the log record that has been flushed to the disk.

stopLogShipment

public void stopLogShipment()

Stop shipping log records. If a ship is currently in progress it will not be interrupted, shipping will stop only after the current shipment is done.

workToDo

public void workToDo()

Used to notify the log shipper that a log buffer element is full. This method would basically use the following steps to decide on the action to be taken when a notification from the log shipper is received, a) Get FI from log buffer b) If FI >= FI_HIGH b.1) notify the log shipper thread. c) Else If the time elapsed since last ship is greater than minShippingInterval c.1) notify the log shipper thread.