Then we look at the status of flink here, we can see that he includes
operator state
keyed state
state backends
Let's first look at what is the state in flink, this is a bit similar to the sum operation we did before, flink is actually, every time
A data will be added once, and then the added data will be put into the memory, and then wait for the next data to come, then take out the addition, add the data that comes, and then add The result of adding up, update the original last addition to the memory, so,
cycle right.
So you can see that the result of saving this sum is actually the saved state.