[jira] [Created] (FLINK-16311) PersistedAppendingBuffer state primitive has incorrect contracts for view() method

[Shang Yuanchun (Jira)]

Tzu-Li (Gordon) Tai created FLINK-16311:
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             Summary: PersistedAppendingBuffer state primitive has incorrect contracts for view() method
                 Key: FLINK-16311
                 URL: https://issues.apache.org/jira/browse/FLINK-16311
             Project: Flink
          Issue Type: Bug
          Components: Stateful Functions
    Affects Versions: statefun-1.1
            Reporter: Tzu-Li (Gordon) Tai
            Assignee: Tzu-Li (Gordon) Tai


The {{PersistedAppendingBuffer}} state primitive in Stateful Functions, states that {{view()}} returns {{null}} if the buffer wasn't accessed before, or after a {{clear()}}.

This actually is not possible. The {{PersistedAppendingBuffer}} primitive is based on Flink's {{ListState}} state handle, which always returns an empty list if the elements of the list is empty, and never a {{null}}.

This means that the {{PersistedAppendingBuffer}} won't be able to differentiate the cases (e.g. if the state wasn't accessed or cleared v.s. an empty buffer).
We suggest to just change the contract so that {{PersistedAppendingBuffer#view()}} follows the behavior of Flink's {{ListState}} to never return null.



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