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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
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 * Unless required by applicable law or agreed to in writing, software
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package org.apache.flink.runtime.state;

import java.io.Serializable;

/**
 * Base of all handles that represent checkpointed state in some form. The object may hold
 * the (small) state directly, or contain a file path (state is in the file), or contain the
 * metadata to access the state stored in some external database.
 *
 * 

State objects define how to {@link #discardState() discard state} and how to access the * {@link #getStateSize() size of the state}. * *

State Objects are transported via RPC between JobManager and * TaskManager and must be {@link java.io.Serializable serializable} to support that. * *

Some State Objects are stored in the checkpoint/savepoint metadata. For long-term * compatibility, they are not stored via {@link java.io.Serializable Java Serialization}, * but through custom serializers. */ public interface StateObject extends Serializable { /** * Discards the state referred to and solemnly owned by this handle, to free up resources in * the persistent storage. This method is called when the state represented by this * object will not be used any more. */ void discardState() throws Exception; /** * Returns the size of the state in bytes. If the the size is not known, this * method should return {@code 0}. * *

The values produced by this method are only used for informational purposes and * for metrics/monitoring. If this method returns wrong values, the checkpoints and recovery * will still behave correctly. However, efficiency may be impacted (wrong space pre-allocation) * and functionality that depends on metrics (like monitoring) will be impacted. * *

Note for implementors: This method should not perform any I/O operations * while obtaining the state size (hence it does not declare throwing an {@code IOException}). * Instead, the state size should be stored in the state object, or should be computable from * the state stored in this object. * The reason is that this method is called frequently by several parts of the checkpointing * and issuing I/O requests from this method accumulates a heavy I/O load on the storage * system at higher scale. * * @return Size of the state in bytes. */ long getStateSize(); }





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