[jira] [Created] (FLINK-30217) Use ListState#update() to replace clear + add mode.

["xljtswf (Jira)" <ji...@apache.org>]

xljtswf created FLINK-30217:
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             Summary: Use ListState#update() to replace clear + add mode.
                 Key: FLINK-30217
                 URL: https://issues.apache.org/jira/browse/FLINK-30217
             Project: Flink
          Issue Type: Improvement
            Reporter: xljtswf


When using listState, I found many times we need to clear current state, then add new values. This is especially common in CheckpointedFunction#snapshotState, which is slower than just use ListState#update().

Suppose we want to update the liststate to contain value1, value2, value3.
With current implementation, we first call Liststate#clear(). this updates the state 1 time.
then we add value1, value2, value3 to the state.
if we use heap state, we need to search the stateTable 3 times and add 3 values to the list.
this happens in memory and is not too bad.
if we use rocksdb. then we will call backend.db.merge() 3 times.
finally, we will  update the state 4 times.
The more values to be added, the more times we will update the state.

while if we use listState#update. then we just need to update the state 1 time. I think this can save a lot of time.






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