voldemort.cluster.failuredetector
Class BannagePeriodFailureDetector

java.lang.Object
  voldemort.cluster.failuredetector.AbstractFailureDetector
      voldemort.cluster.failuredetector.BannagePeriodFailureDetector

All Implemented Interfaces:

FailureDetector

public class BannagePeriodFailureDetector
extends AbstractFailureDetector

BannagePeriodFailureDetector relies on external callers to notify it of failed attempts to access a node's store via recordException. When recordException is invoked, the node is marked offline for a period of time as defined by the client or server configuration. Once that period has passed, the node is considered available. However, BannagePeriodFailureDetector's definition of available uses a fairly loose sense of the word. Rather than considering the node to be available for access, it is available for attempting to access. In actuality the node may still be down. However, the intent is simply to mark it down for N seconds and then attempt to try again and repeat. If the node is truly available for access, the caller will then invoke recordSuccess and the node will be marked available in the truest sense of the word.

See Also:

VoldemortConfig.getFailureDetectorBannagePeriod(), ClientConfig.getFailureDetectorBannagePeriod(), FailureDetectorConfig.getBannagePeriod()

Field Summary

Fields inherited from class voldemort.cluster.failuredetector.AbstractFailureDetector

failureDetectorConfig, listeners, logger, nodeStatusMap

Constructor Summary

BannagePeriodFailureDetector(FailureDetectorConfig failureDetectorConfig)

Method Summary

java.lang.String	getUnavailableNodesBannageExpiration()
boolean	isAvailable(Node node) Determines if the node is available or offline.
void	recordException(Node node, long requestTime, UnreachableStoreException e) Allows external callers to provide input to the FailureDetector that an error occurred when trying to access the node.
void	recordSuccess(Node node, long requestTime) Allows external callers to provide input to the FailureDetector that an access to the node succeeded.

Methods inherited from class voldemort.cluster.failuredetector.AbstractFailureDetector

addFailureDetectorListener, checkArgs, checkNodeArg, destroy, getAvailableNodeCount, getAvailableNodes, getConfig, getLastChecked, getNodeCount, getNodeStatus, getUnavailableNodes, removeFailureDetectorListener, setAvailable, setUnavailable, waitForAvailability

Methods inherited from class java.lang.Object

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

Constructor Detail

BannagePeriodFailureDetector

public BannagePeriodFailureDetector(FailureDetectorConfig failureDetectorConfig)

Method Detail

isAvailable

public boolean isAvailable(Node node)

Description copied from interface: FailureDetector

Determines if the node is available or offline. The isAvailable method is a simple boolean operation to determine if the node in question is available. As expected, the result of this call is an approximation given race conditions. However, the FailureDetector should do its best to determine the then-current state of the cluster to produce a minimum of false negatives and false positives.

Note: this determination is approximate and differs based upon the algorithm used by the implementation.

Parameters:

node - Node to check

Returns:

True if available, false otherwise

recordException

public void recordException(Node node,
                            long requestTime,
                            UnreachableStoreException e)

Description copied from interface: FailureDetector

Allows external callers to provide input to the FailureDetector that an error occurred when trying to access the node. The implementation is free to use or ignore this input. It can be considered a "hint" to the FailureDetector rather than an absolute truth. For example, it is possible to call recordException for a given node and have an immediate call to isAvailable return true, depending on the implementation.

Parameters:

node - Node to check

requestTime - Length of time (in milliseconds) to perform request

e - Exception that occurred when trying to access the node

recordSuccess

public void recordSuccess(Node node,
                          long requestTime)

Description copied from interface: FailureDetector

Allows external callers to provide input to the FailureDetector that an access to the node succeeded. As with recordException, the implementation is free to use or ignore this input. It can be considered a "hint" to the FailureDetector rather than gospel truth.

Note for implementors: because of threading issues it's possible for multiple threads to attempt access to a node and some fail and some succeed. In a classic last-one-in-wins scenario, it's possible for the failures to be recorded first and then the successes. It would be prudent for implementations not to immediately assume that the node is then available.

Parameters:

node - Node to check

requestTime - Length of time (in milliseconds) to perform request

getUnavailableNodesBannageExpiration

public java.lang.String getUnavailableNodesBannageExpiration()