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https://issues.apache.org/jira/browse/FLINK-12005?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17362401#comment-17362401
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J Y commented on FLINK-12005:
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it would be really cool to have a hook on expiration of state. the use case
for us is to do something as the state is expiring (e.g. accumulate enough
other state to do some operation that's an approximation based on the state
available upon expiration).
> [State TTL] Event time support
> ------------------------------
>
> Key: FLINK-12005
> URL: https://issues.apache.org/jira/browse/FLINK-12005
> Project: Flink
> Issue Type: New Feature
> Components: API / DataStream, Runtime / State Backends
> Reporter: Andrey Zagrebin
> Priority: Major
> Labels: auto-unassigned, stale-major
>
> The event time is opted for in StateTtlConfig by setting
> TtlTimeCharacteristic.EventTime.
> To enable event time support, the updated watermark needs to be passed to the
> state backend, shared with TTL state wrappers and additional cleanup
> strategies (snapshot transformers and compaction filter).
> h3. Event time provider
> Additional implementation of TtlTimeProvider, which holds current watermark,
> needs to be passed to the state backend at the moment of its creation in
> StreamTaskStateInitializerImpl. There several ways to update watermark in
> this implementation of TtlTimeProvider:
> * in InternalTimeServiceManager.advanceWatermark explicitly
> * InternalTimeServiceManager/InternalTimerServiceImpl could be refactored to
> use shared EventTimeService which holds current updatable watermark and
> wrapped by TtlTimeProvider
> The TTL state wrapping factory should create TTL state wrappers and snapshot
> transformers with TtlTimeProvider selected by TtlTimeCharacteristic.
> h3. RocksDB TTL compaction filter
> The RocksDB TTL compaction filter factory needs to get selected
> TtlTimeProvider when it gets configured. There are two ways:
> * make it volatile and settable in
> RocksDbTtlCompactFiltersManager.TimeProviderWrapper, track it in
> RocksDbTtlCompactFiltersManager along with FlinkCompactionFilterFactory to
> configure later before configuring FlinkCompactionFilterFactory.
> * Move FlinkCompactionFilter.TimeProvider from FlinkCompactionFilterFactory
> to ConfigHolder and set selected TtlTimeProvider with the Config.
> The second option does not use volatile variable and should be more
> performant but needs changing RocksDB java client and either releasing new
> version FRocksDB or Flink RocksDB extensions.
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