org.apache.hadoop.hdfs.server.namenode.ha

Interface HAContext

All Known Implementing Classes:

NameNode.NameNodeHAContext

@InterfaceAudience.Private
public interface HAContext

Context that is to be used by HAState for getting/setting the current state and performing required operations.

Method Summary

Methods

Modifier and Type	Method and Description
boolean	allowStaleReads()
void	checkOperation(NameNode.OperationCategory op) Verify that the given operation category is allowed in the current state.
HAState	getState() Get the state from the context
void	prepareToStopStandbyServices() Prepare to exit the standby state
void	setState(HAState state) Set the state of the context to given state
void	startActiveServices() Start the services required in active state
void	startStandbyServices() Start the services required in standby state
void	stopActiveServices() Stop the services when exiting active state
void	stopStandbyServices() Stop the services when exiting standby state
void	writeLock() Take a write-lock on the underlying namesystem so that no concurrent state transitions or edits can be made.
void	writeUnlock() Unlock the lock taken by writeLock()

Method Detail

setState

void setState(HAState state)

Set the state of the context to given state

getState

HAState getState()

Get the state from the context

startActiveServices

void startActiveServices()
                         throws IOException

Start the services required in active state

Throws:

IOException

stopActiveServices

void stopActiveServices()
                        throws IOException

Stop the services when exiting active state

Throws:

IOException

startStandbyServices

void startStandbyServices()
                          throws IOException

Start the services required in standby state

Throws:

IOException

prepareToStopStandbyServices

void prepareToStopStandbyServices()
                                  throws ServiceFailedException

Prepare to exit the standby state

Throws:

ServiceFailedException

stopStandbyServices

void stopStandbyServices()
                         throws IOException

Stop the services when exiting standby state

Throws:

IOException

writeLock

void writeLock()

Take a write-lock on the underlying namesystem so that no concurrent state transitions or edits can be made.

writeUnlock

void writeUnlock()

Unlock the lock taken by writeLock()

checkOperation

void checkOperation(NameNode.OperationCategory op)
                    throws StandbyException

Verify that the given operation category is allowed in the current state. This is to allow NN implementations (eg BackupNode) to override it with node-specific handling. If the operation which is being checked will be taking the FSNS lock, it's advisable to check the operation category both immediately before and after taking the lock. This is because clients rely on the StandbyException thrown by this method in order to trigger client failover, and if a client first tries to contact the Standby NN, it could block for a long time if the Standby is holding the lock for a while, e.g. when performing a checkpoint. See HDFS-4591 for more details.

Throws:

StandbyException

allowStaleReads

boolean allowStaleReads()

Returns:

true if the node should allow stale reads (ie reads while the namespace is not up to date)