oracle.kv
Class Consistency.Time

java.lang.Object
  oracle.kv.Consistency
      oracle.kv.Consistency.Time

All Implemented Interfaces:

Serializable, oracle.kv.impl.util.FastExternalizable

Enclosing class:

Consistency

public static class Consistency.Time
extends Consistency

A consistency policy which describes the amount of time the Replica is allowed to lag the Master. The application can use this policy to ensure that the Replica node sees all transactions that were committed on the Master before the lag interval.

Effective use of this policy requires that the clocks on the Master and Replica are synchronized by using a protocol like NTP.

Consistency Timeout

Besides the lag time, this class has a timeout attribute. The timeout controls how long a Replica may wait for the desired consistency to be achieved before giving up.

All KVStore read operations support a Consistency specification, as well as a separate operation timeout. The KVStore client driver implements a read operation by choosing a node (usually a Replica) from the proper replication group, and sending it a request. If the Replica cannot guarantee the desired Consistency within the Consistency timeout, it replies to the request with a failure indication. If there is still time remaining within the operation timeout, the client driver picks another node and tries the request again (transparent to the application).

It makes sense to think of the operation timeout as the maximum amount of time the application is willing to wait for the operation to complete. The Consistency timeout is like a performance hint to the implementation, suggesting that it can generally expect that a healthy Replica usually should be able to become consistent within the given amount of time, and that if it doesn't, then it is probably more likely worth the overhead of abandoning the request attempt and retrying with a different replica. Note that for the Consistency timeout to be meaningful it must be smaller than the operation timeout.

Choosing a value for the operation timeout depends on the needs of the application. Finding a good Consistency timeout value is more likely to depend on observations made of real system performance.

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class oracle.kv.Consistency

Consistency.Time, Consistency.Version

Field Summary

Fields inherited from class oracle.kv.Consistency

ABSOLUTE, NONE_REQUIRED

Constructor Summary

Consistency.Time(long permissibleLag, TimeUnit permissibleLagUnit, long timeout, TimeUnit timeoutUnit)
Specifies the amount of time by which the Replica is allowed to lag the master when initiating a transaction.

Method Summary

boolean	equals(Object obj)
String	getName() Returns the name used to identify the policy.
long	getPermissibleLag(TimeUnit unit) Returns the allowed time lag associated with this policy.
long	getTimeout(TimeUnit unit) Returns the consistency timeout associated with this policy.
int	hashCode()
String	toString()

Methods inherited from class oracle.kv.Consistency

fromByteArray, toByteArray

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface oracle.kv.impl.util.FastExternalizable

writeFastExternal

Constructor Detail

Consistency.Time

public Consistency.Time(long permissibleLag,
                        TimeUnit permissibleLagUnit,
                        long timeout,
                        TimeUnit timeoutUnit)

Specifies the amount of time by which the Replica is allowed to lag the master when initiating a transaction. The Replica ensures that all transactions that were committed on the Master before this lag interval are available at the Replica before allowing a transaction to proceed.

Effective use of this policy requires that the clocks on the Master and Replica are synchronized by using a protocol like NTP.

Parameters:

permissibleLag - the time interval by which the Replica may be out of date with respect to the Master when a transaction is initiated on the Replica.

permissibleLagUnit - the TimeUnit for the permissibleLag parameter.

timeout - the amount of time to wait for the consistency to be reached.

timeoutUnit - the TimeUnit for the timeout parameter.

Method Detail

getName

public String getName()

Description copied from class: Consistency

Returns the name used to identify the policy.

Specified by:

getName in class Consistency

getPermissibleLag

public long getPermissibleLag(TimeUnit unit)

Returns the allowed time lag associated with this policy.

Parameters:

unit - the TimeUnit of the returned value.

Returns:

the permissible lag time in the specified unit.

getTimeout

public long getTimeout(TimeUnit unit)

Returns the consistency timeout associated with this policy.

Parameters:

unit - the TimeUnit of the returned value.

Returns:

the consistency timeout in the specified unit.

hashCode

public int hashCode()

Overrides:

hashCode in class Object

equals

public boolean equals(Object obj)

Overrides:

equals in class Object

toString

public String toString()

Overrides:

toString in class Object