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https://issues.apache.org/jira/browse/FLINK-3089?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16341433#comment-16341433
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Bowen Li commented on FLINK-3089:
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[~srichter] Right, we should implement it in both backends, and also give users
a heads-up that TTL's heap implementation would increase their in-memory state
size and they should consider it in memory capacity planning.
I actually did some research yesterday on how TTL should be implemented in
memory. What you described is very similar to [how Redis implemented
TTL|https://redis.io/commands/expire#how-redis-expires-keys], and, of course,
we need to cater the strategy to Flink.
How about this? Let me summarize all the above discussions and write up a
google doc, and then we can iterate on the design
> State API Should Support Data Expiration (State TTL)
> ----------------------------------------------------
>
> Key: FLINK-3089
> URL: https://issues.apache.org/jira/browse/FLINK-3089
> Project: Flink
> Issue Type: New Feature
> Components: DataStream API, State Backends, Checkpointing
> Reporter: Niels Basjes
> Assignee: Bowen Li
> Priority: Major
>
> In some usecases (webanalytics) there is a need to have a state per visitor
> on a website (i.e. keyBy(sessionid) ).
> At some point the visitor simply leaves and no longer creates new events (so
> a special 'end of session' event will not occur).
> The only way to determine that a visitor has left is by choosing a timeout,
> like "After 30 minutes no events we consider the visitor 'gone'".
> Only after this (chosen) timeout has expired should we discard this state.
> In the Trigger part of Windows we can set a timer and close/discard this kind
> of information. But that introduces the buffering effect of the window (which
> in some scenarios is unwanted).
> What I would like is to be able to set a timeout on a specific state which I
> can update afterwards.
> This makes it possible to create a map function that assigns the right value
> and that discards the state automatically.
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