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/*
* Licensed to the Apache Software Foundation (ASF) under one or more contributor license
* agreements. See the NOTICE file distributed with this work for additional information regarding
* copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the License. You may obtain a
* copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License
* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
* or implied. See the License for the specific language governing permissions and limitations under
* the License.
*/
package org.apache.geode;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
/**
* 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 {@link
* DataOutput} and {@link DataInput} parameters.
*
* @since GemFire 6.1
*/
public interface Delta {
/**
* 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.
*
* @return whether this object has pending changes it can write out as a delta
*/
boolean hasDelta();
/**
* This method is invoked on an application object at the delta sender, if GemFire determines the
* presence of a delta by calling {@link Delta#hasDelta()} on the object. The delta is written to
* the {@link DataOutput} object provided by GemFire.
*
*
* Any delta state should be reset in this method.
*
* @param out the {@link DataOutput} to write to
* @throws IOException if a problem occurs while writing to out
*/
void toDelta(DataOutput out) throws IOException;
/**
* This method is invoked on an existing application object when an update is received as a delta.
* This method throws an {@link InvalidDeltaException} when the delta in the {@link DataInput}
* cannot be applied to the object. GemFire automatically handles an {@link InvalidDeltaException}
* by reattempting the update by sending the full application object.
*
* @param in the {@link DataInput} to read from
* @throws IOException if a problem occurs while reading from in
*/
void fromDelta(DataInput in) throws IOException, InvalidDeltaException;
/**
* 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.
*
* @return whether entry sizes should be recalculated when deltas are applied
* @since 1.14
*/
default boolean getForceRecalculateSize() {
return false;
}
}