dalongliu created FLINK-17099:
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Summary: Refactoring State TTL solution in Group Agg、TopN
operator, etc replace Timer with StateTtlConfig
Key: FLINK-17099
URL: https://issues.apache.org/jira/browse/FLINK-17099
Project: Flink
Issue Type: Improvement
Components: Table SQL / Runtime
Affects Versions: 1.10.0, 1.9.0
Reporter: dalongliu
Fix For: 1.11.0
At the moment, there are 2 ways to cleanup states.
1) registering a processing-time timer, and cleanup entries when the timer is
callback.
- pros: can cleanup multiple states at the same time (state consistent)
- cons: timer space depends on the key size, which may lead to OOM (heap
timer).
- used in Group Aggregation, Over Aggregation, TopN
2) using the {{StateTtlConfig}} provided by DataStream [1].
- pros: decouple the logic of state ttl with the record processing, easy to
program (take a look at old planner NonWindowJoin which bundles ttl timestamp
with records in MapState).
- cons: can't cleanup multiple states at the same time.
- useed in Sream-Stream Joins.
For timer solution, although it can cleanup multiple states at the same time,
but it also will lead to OOM when there have a great many state keys, besides,
StateTtlConfig is used in stream-stream join case, and will be used in more
operator. Therefore，in order to unify the state ttl solution, simplify the code
implemention, and improve the readability of codes, so we should refactor state
cleanup way which use StateTtlConfig to replace processing-time timer in Group
Aggregation、Over Aggregation、TopN operator, etc.
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