[jira] [Created] (FLINK-18060) Add notice for heap-based state backend of state access reference problem

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

Yun Tang created FLINK-18060:
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             Summary: Add notice for heap-based state backend of state access reference problem
                 Key: FLINK-18060
                 URL: https://issues.apache.org/jira/browse/FLINK-18060
             Project: Flink
          Issue Type: Bug
          Components: Documentation
            Reporter: Yun Tang


Currently, when talking about the limitation of {{MemoryStateBackend}} and {{FsStateBackend}} in [documentation|https://ci.apache.org/projects/flink/flink-docs-stable/ops/state/state_backends.html#the-memorystatebackend], Flink only focus on the memory checkpoint size limit. However, current documentation forgets to talk about the reference problem, which added in {{CopyOnWriteStateMap}}:

{noformat}
IMPORTANT: the contracts for this class rely on the user not holding any references to objects returned by this map beyond the life cycle of per-element operations. Or phrased differently, all get-update-put operations on a mapping should be within one call of processElement. Otherwise, the user must take care of taking deep copies, e.g. for caching purposes.
{noformat}

This actually also applies to {{NestedStateMap}}.




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