Apache Flink:当我修改存储的对象时，MapState 是否会自动更新? [英] Apache Flink: Is MapState automatically updated when I modify a stored object?

问题描述

是否需要使用MapState.put()手动更新状态或者修改对象时状态是否自动更新?

Is it necessary to use MapState.put() to manually update the state or whether is the state automatically updated when I modify an object?

private transient MapState<String, Word> words;
.......
Word w = words.get(word);             
if (w == null) {
  w = new Word(word);
  //words.put(word, w);  //A
}              
if (....) {
  w.countBad(1);   // countXXX modifies a the private variable in a Word object 
} else {
  w.countGood(1);
}    
//words.put(word, w);   //B

Q:如果我使用A方法，下一次计数计算是否会自动更新对应的Mapstate状态?还是需要在计算完成后使用B方法手动更新状态?

Q: If I use the A method, will the next count calculation automatically update the corresponding Mapstate state? Or do I need to use the B method to manually update the state after the calculation is complete?

推荐答案

从 API 的角度来看，您总是需要手动更新状态.

From an API point of view, you always need to manually update the state.

然而，实际行为取决于状态后端.如果应用程序使用InMemoryStateBackend 或FsStateBackend，则所有本地状态都存储在工作进程的JVM 堆中，即状态后端只保存对对象的引用.因此，当您修改对象时，状态会直接被修改.

However, the actual behavior depends on the state backend. If the application uses the InMemoryStateBackend or the FsStateBackend, all local state is stored on the JVM heap of the worker process, i.e., the state backend just holds a reference to the object. Hence, the state is directly modified when you modify the object.

如果您使用 RocksDBStateBackend，所有状态访问都会被反序列化并从 RocksDB 读取/写入.在这种情况下，修改对象不会影响状态.

If you use the RocksDBStateBackend all state accesses are de/serialized and read from / written to RocksDB. In this case modifying the object does not have an effect on the state.

我建议始终显式更新状态，因为这将确保您可以在不调整应用程序逻辑的情况下切换状态后端.

I recommend to always explicitly update the state because this will ensure that you can switch the state backend without adjusting the logic of your application.

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