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https://issues.apache.org/jira/browse/FLINK-14197?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16938961#comment-16938961
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Kenneth William Krugler commented on FLINK-14197:
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I would suggest posting to the mailing list, as you'll (a) get input from the
larger Flink community, and (b) the discussion is more visible and thus useful
to other users.
> Increasing trend for state size of keyed stream using ProcessWindowFunction
> with ProcessingTimeSessionWindows
> -------------------------------------------------------------------------------------------------------------
>
> Key: FLINK-14197
> URL: https://issues.apache.org/jira/browse/FLINK-14197
> Project: Flink
> Issue Type: Bug
> Components: Runtime / Checkpointing, Runtime / State Backends
> Affects Versions: 1.9.0
> Environment: Tested with:
> * Local Flink Mini Cluster running from IDE
> * Flink standalone cluster run in docker
> Reporter: Oliver Kostera
> Priority: Major
>
> I'm using *ProcessWindowFunction* in a keyed stream with the following
> definition:
> {code:java}
> final SingleOutputStreamOperator<Message> processWindowFunctionStream
> =
>
> keyedStream.window(ProcessingTimeSessionWindows.withGap(Time.milliseconds(100)))
> .process(new
> CustomProcessWindowFunction()).uid(PROCESS_WINDOW_FUNCTION_OPERATOR_ID)
> .name("Process window function");
> {code}
> My checkpointing configuration is set to use RocksDB state backend with
> incremental checkpointing and EXACTLY_ONCE mode.
> In a runtime I noticed that even though data ingestion is static - same keys
> and frequency of messages the size of the process window operator keeps
> increasing. I tried to reproduce it with minimal similar setup here:
> https://github.com/loliver1234/flink-process-window-function and was
> successful to do so.
> Testing conditions:
> - RabbitMQ source with Exactly-once guarantee and 65k prefetch count
> - RabbitMQ sink to collect messages
> - Simple ProcessWindowFunction that only pass messages through
> - Stream time characteristic set to TimeCharacteristic.ProcessingTime
> Testing scenario:
> - Start flink job and check initial state size - State Size: 127 KB
> - Start sending messages, 1000 same unique keys every 1s (they are not
> falling into defined time window gap set to 100ms, each message should create
> new window)
> - State of the process window operator keeps increasing - after 1mln messages
> state ended up to be around 2mb
> - Stop sending messages and wait till rabbit queue is fully consumed and few
> checkpoints go by
> - Was expected to see state size to decrease to base value but it stayed at
> 2mb
> - Continue to send messages with the same keys and state kept increasing
> trend.
> What I checked:
> - Registration and deregistration of timestamps set for time windows - each
> registration matched its deregistration
> - Checked that in fact there are no window merges
> - Tried custom Trigger disabling window merges and setting onProcessingTime
> trigger to TriggerResult.FIRE_AND_PURGE - same state behavior
> On staging environment, we noticed that state for that operator keeps
> increasing indefinitely, after some months reaching even 1,5gb for 100k
> unique keys
> Flink commit id: 9c32ed9
>
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