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com.tangosol.net.partition
Class FailoverAccessPolicy

java.lang.Object
com.tangosol.net.partition.FailoverAccessPolicy

All Implemented Interfaces:

ActionPolicy

public class FailoverAccessPolicy

extends java.lang.Object

implements ActionPolicy

FailoverAccessPolicy is used to moderate the client request load during a failover event in order to allow cache servers adequate opportunity to re-establish partition backups.

While typically not necessary to ensure the timely recovery to a "safe" state, this access policy could be used in situations where a heavy load of of high-latency requests may prevent or significantly delay cache servers from successfully acquiring exclusive access to partitions needing to be transferred or backed up.

Since:

Coherence 12.1.2

Author:

rhl 09.12.2011

Nested Class Summary

protected class

FailoverAccessPolicy.MembershipListener The MemberListener is used to listen to service membership events to monitor the endangered status of the service.

Field Summary

long	m_cLimitMillis The amount of time after being in an endangered state after which the quorum policy makes a maximal effort to hold client requests.
long	m_cMaxDelayMillis The maximum amount of time (in ms) that a request could be delayed by this quorum policy.
long	m_cThresholdMillis The amount of time after being in an endangered state before the quorum policy should start to hold client requests.
long	m_ldtEndangered The time at which the service most recently became endangered (or 0 if the service is in the "safe" state).
int	m_nState One of the STATE_* constants representing the current quorum state.
protected PartitionedService	m_service The PartitionedService that this quorum policy is bound to.
static int	STATE_ENDANGERED Constant used to indicate that the service is in an endangered state.
static int	STATE_SAFE Constant used to indicate that the service is "safe" (non-endangered).
static int	STATE_UNKNOWN Constant used to indicate that the service is in an unknown (possibly endangered) state.

Constructor Summary

FailoverAccessPolicy()
Default constructor.

FailoverAccessPolicy(long cThresholdMillis, long cLimitMillis, long cMaxDelayMillis)
Construct a FailoverAccessPolicy according to the specified parameters.

Method Summary

protected long	calculateWaitTime(long cMillisEndangered) Return the amount of time that a request should be delayed before being allowed to proceed.
protected boolean	checkEndangered() Check to see if the associated service is endangered.
int	getState() Return the current endangered state (one of the STATE_* constants).
void	init(Service service) Called when the specified service loads and configures this policy.
boolean	isAllowed(Service service, Action action) Evaluate if the specified action is currently allowed by this policy.
protected void	setState(int nState) Set the endangered state (one of the STATE_* constants).

Methods inherited from interface com.tangosol.net.ActionPolicy

toString

Field Detail

STATE_SAFE

public static final int STATE_SAFE

Constant used to indicate that the service is "safe" (non-endangered).

See Also:

Constant Field Values

STATE_UNKNOWN

public static final int STATE_UNKNOWN

Constant used to indicate that the service is in an unknown (possibly endangered) state.

See Also:

Constant Field Values

STATE_ENDANGERED

public static final int STATE_ENDANGERED

Constant used to indicate that the service is in an endangered state.

See Also:

Constant Field Values

m_cThresholdMillis

public long m_cThresholdMillis

The amount of time after being in an endangered state before the quorum policy should start to hold client requests.

m_cLimitMillis

public long m_cLimitMillis

The amount of time after being in an endangered state after which the quorum policy makes a maximal effort to hold client requests.

m_cMaxDelayMillis

public long m_cMaxDelayMillis

The maximum amount of time (in ms) that a request could be delayed by this quorum policy.

m_nState

public int m_nState

One of the STATE_* constants representing the current quorum state.

Note: this field is intentionally left non-volatile. The consequence of a "stale" read is that the first request per thread following a transition to endangered could be missed by this quorum (allowed to proceed). As this has no impact, we would rather avoid the additional volatile read on each "normal" operation.

m_ldtEndangered

public long m_ldtEndangered

The time at which the service most recently became endangered (or 0 if the service is in the "safe" state).

m_service

protected PartitionedService m_service

The PartitionedService that this quorum policy is bound to.

Constructor Detail

FailoverAccessPolicy

public FailoverAccessPolicy()

Default constructor.

FailoverAccessPolicy

public FailoverAccessPolicy(long cThresholdMillis,
                            long cLimitMillis,
                            long cMaxDelayMillis)

Construct a FailoverAccessPolicy according to the specified parameters.

Parameters:

cThresholdMillis - the delay before the policy should start holding requests (after becoming endangered)

cLimitMillis - the delay before the policy makes a maximal effort to hold requests (after becoming endangered)

cMaxDelayMillis - the maximum amount of time to hold a request

Method Detail

getState

public int getState()

Return the current endangered state (one of the STATE_* constants).

Returns:

the current endangered state

setState

protected void setState(int nState)

Set the endangered state (one of the STATE_* constants).

Parameters:

nState - the new endangered state

init

public void init(Service service)

Called when the specified service loads and configures this policy.

Note: A policy could be applied to multiple services.

Specified by:

init in interface ActionPolicy

Parameters:

service - the service that this policy applies to

isAllowed

public boolean isAllowed(Service service,
                         Action action)

Evaluate if the specified action is currently allowed by this policy.

Note: for forward compatibility, implementations should generally return true for actions that are not recognized.

Specified by:

isAllowed in interface ActionPolicy

Parameters:

service - the service that is performing the action

action - the action that is being performed

Returns:

true iff the specified action is currently allowed by this policy

calculateWaitTime

protected long calculateWaitTime(long cMillisEndangered)

Return the amount of time that a request should be delayed before being allowed to proceed.

Parameters:

cMillisEndangered - the amount of time that the service has been endangered

Returns:

the amount of time (in ms) to delay the client request

checkEndangered

protected boolean checkEndangered()

Check to see if the associated service is endangered.

Note: the caller must hold synchronization on this quorum policy.

Returns:

true iff the service is endangered

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