Aljoscha Krettek created FLINK-3201:
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Summary: Enhance Partitioned State Interface with State Types
Key: FLINK-3201
URL: https://issues.apache.org/jira/browse/FLINK-3201
Project: Flink
Issue Type: Sub-task
Components: Streaming
Affects Versions: 1.0.0
Reporter: Aljoscha Krettek
Assignee: Aljoscha Krettek
We should enhance the partitioned state with different state types, so that the
system knows about the semantics of the State. I propose for now:
- ValueState, this behaves like the current OperatorState: state is one value
that can be set and retrieved
- ListState, state is a list that can be appended to and iterated over
- ReducingState, state is one value that other values can be added to
ListState and ReducingState would share a common superclass to allow them to be
used in the same places. For example, the WindowOperator would use
ReducingState and ListState interchangeably, depending on whether we have a
ReduceFunction or not.
These additions allow the system to be clever about how state is checkpointed
in the future. Think ManageMemory/Out-of-core state and incremental checkpoints.
Also, state should be scoped to both a key and a namespace. This will allow the
WindowOperator to use the interface. Right now, WindowOperator has a custom
state implementation that uses a two-level Map (by key and by window). In this
case the window would be the namespace.
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