org.apache.geode

Interface Delta

All Known Implementing Classes:

DeltaSession, DeltaSession7, DeltaSession8, DeltaSession9

public interface Delta

This interface defines a contract between the application and GemFire that allows GemFire to determine whether an application object contains a delta, allows GemFire to extract the delta from an application object, and generate a new application object by applying a delta to an existing application object. The difference in object state is contained in the DataOutput and DataInput parameters.

Since:

GemFire 6.1

Method Summary

Modifier and Type	Method and Description
void	fromDelta(DataInput in) This method is invoked on an existing application object when an update is received as a delta.
default boolean	getForceRecalculateSize() By default, entry sizes are not recalculated when deltas are applied.
boolean	hasDelta() Returns true if this object has pending changes it can write out as a delta.
void	toDelta(DataOutput out) This method is invoked on an application object at the delta sender, if GemFire determines the presence of a delta by calling hasDelta() on the object.

Method Detail

hasDelta

boolean hasDelta()

Returns true if this object has pending changes it can write out as a delta. Returns false if this object must be transmitted in its entirety.

Returns:

whether this object has pending changes it can write out as a delta

toDelta

void toDelta(DataOutput out)
      throws IOException

This method is invoked on an application object at the delta sender, if GemFire determines the presence of a delta by calling hasDelta() on the object. The delta is written to the DataOutput object provided by GemFire.

Any delta state should be reset in this method.

Parameters:

out - the DataOutput to write to

Throws:

IOException - if a problem occurs while writing to out

fromDelta

void fromDelta(DataInput in)
        throws IOException,
               InvalidDeltaException

This method is invoked on an existing application object when an update is received as a delta. This method throws an InvalidDeltaException when the delta in the DataInput cannot be applied to the object. GemFire automatically handles an InvalidDeltaException by reattempting the update by sending the full application object.

Parameters:

in - the DataInput to read from

Throws:

IOException - if a problem occurs while reading from in

InvalidDeltaException

getForceRecalculateSize

default boolean getForceRecalculateSize()

By default, entry sizes are not recalculated when deltas are applied. This optimizes for the case where the size of an entry does not change. However, if an entry size does increase or decrease, this default behavior can result in the memory usage statistics becoming inaccurate. These are used to monitor the health of Geode instances, and for balancing memory usage across partitioned regions.

There is a system property, gemfire.DELTAS_RECALCULATE_SIZE, which can be used to cause all deltas to trigger entry size recalculation when deltas are applied. By default, this is set to 'false' because of potential performance impacts when every delta triggers a recalculation.

To allow entry size recalculation on a per-delta basis, classes that extend the Delta interface should override this method to return 'true'. This may impact performance of specific delta types, but will not globally affect the performance of other Geode delta operations.

Returns:

whether entry sizes should be recalculated when deltas are applied

Since:

1.14