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https://issues.apache.org/jira/browse/FLINK-16686?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17101509#comment-17101509
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Andrey Zagrebin commented on FLINK-16686:
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Unfortunately, I cannot suggest more than it is written in the original
stackoverflow discussion:
As a workaround, I would suggest to use a list state with simple elements which
type has a fixed byte length when serialized. That would be primitive types and
POJOs, maybe implement a custom fixed length serializer if possible. Then the
non-fixed length (Kryo or Chill) serializer does not have to be called in the
TTL cleanup and the TTL cleanup would not require the user class loader.
> [State TTL] Make user class loader available in native RocksDB compaction
> thread
> --------------------------------------------------------------------------------
>
> Key: FLINK-16686
> URL: https://issues.apache.org/jira/browse/FLINK-16686
> Project: Flink
> Issue Type: Bug
> Components: Runtime / State Backends
> Affects Versions: 1.8.0
> Reporter: Andrey Zagrebin
> Priority: Major
>
> The issue is initially reported
> [here|https://stackoverflow.com/questions/60745711/flink-kryo-serializer-because-chill-serializer-couldnt-be-found].
> The problem is that the java code of Flink compaction filter is called from
> RocksDB native C++ code. It is called in the context of the native compaction
> thread. RocksDB has utilities to create java Thread context for the Flink
> java callback. Presumably, the Java thread context class loader is not set at
> all and if it is queried then it produces NullPointerException.
> The provided report enabled a list state with TTL. The compaction filter has
> to deserialise elements to check expiration. The deserialiser relies on Kryo
> which queries the thread context class loader which is expected to be the
> user class loader of the task but turns out to be null.
> We should investigate how to pass the user class loader to the compaction
> thread of the list state with TTL.
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