Yu Li created FLINK-12692:
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Summary: Support disk spilling in HeapKeyedStateBackend
Key: FLINK-12692
URL: https://issues.apache.org/jira/browse/FLINK-12692
Project: Flink
Issue Type: New Feature
Components: Runtime / State Backends
Reporter: Yu Li
Assignee: Yu Li
{{HeapKeyedStateBackend}} is one of the two {{KeyedStateBackends}} in Flink,
since state lives as Java objects on the heap and the de/serialization only
happens during state snapshot and restore, it outperforms
{{RocksDBKeyedStateBackend}} when all data could reside in memory.
However, along with the advantage, {{HeapKeyedStateBackend}} also has its
shortcomings, and the most painful one is the difficulty to estimate the
maximum heap size (Xmx) to set, and we will suffer from GC impact once the heap
memory is not enough to hold all state data. There’re several (inevitable)
causes for such scenario, including (but not limited to):
* Memory overhead of Java object representation (tens of times of the
serialized data size).
* Data flood caused by burst traffic.
* Data accumulation caused by source malfunction.
To resolve this problem, we propose a solution to support spilling state data
to disk before heap memory is exhausted. We will monitor the heap usage and
choose the coldest data to spill, and reload them when heap memory is regained
after data removing or TTL expiration, automatically.
More details please refer to the design doc and mailing list discussion.
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