[FLINK-6061] NPE on TypeSerializer.serialize with a RocksDBStateBackend calling entries() on a keyed state in the open() function

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.3.0
• Fix Version/s: 1.3.0
• Component/s: API / DataStream, Runtime / State Backends
• Assignee: Stefan Richter
• Reporter: Vladislav Pernin
• Created: 15/Mar/17 10:44
• Updated: 28/Feb/19 10:45
• Resolved: 15/Mar/17 14:31

Description

With a default state (heap), the call to state.entries() "nicely fails" with a IllegalStateException :

Caused by: java.lang.IllegalStateException: No key set.
	at org.apache.flink.util.Preconditions.checkState(Preconditions.java:195)
	at org.apache.flink.runtime.state.heap.HeapMapState.entries(HeapMapState.java:188)
	at org.apache.flink.runtime.state.UserFacingMapState.entries(UserFacingMapState.java:77)
	at org.apache.flink.Reproducer$FailingMapWithState.open(Reproducer.java:78)
	at org.apache.flink.api.common.functions.util.FunctionUtils.openFunction(FunctionUtils.java:36)
	at org.apache.flink.streaming.api.operators.AbstractUdfStreamOperator.open(AbstractUdfStreamOperator.java:112)
	at org.apache.flink.streaming.runtime.tasks.StreamTask.openAllOperators(StreamTask.java:376)
	at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:252)
	at org.apache.flink.runtime.taskmanager.Task.run(Task.java:670)
	at java.lang.Thread.run(Thread.java:745)

With a RocksDBStateBackend, it fails with a NPE :

Caused by: java.lang.NullPointerException
	at org.apache.flink.api.common.typeutils.base.ShortSerializer.serialize(ShortSerializer.java:64)
	at org.apache.flink.api.common.typeutils.base.ShortSerializer.serialize(ShortSerializer.java:27)
	at org.apache.flink.contrib.streaming.state.AbstractRocksDBState.writeKey(AbstractRocksDBState.java:181)
	at org.apache.flink.contrib.streaming.state.AbstractRocksDBState.writeKeyWithGroupAndNamespace(AbstractRocksDBState.java:163)
	at org.apache.flink.contrib.streaming.state.AbstractRocksDBState.writeCurrentKeyWithGroupAndNamespace(AbstractRocksDBState.java:148)
	at org.apache.flink.contrib.streaming.state.RocksDBMapState.serializeCurrentKeyAndNamespace(RocksDBMapState.java:263)
	at org.apache.flink.contrib.streaming.state.RocksDBMapState.iterator(RocksDBMapState.java:196)
	at org.apache.flink.contrib.streaming.state.RocksDBMapState.entries(RocksDBMapState.java:143)
	at org.apache.flink.runtime.state.UserFacingMapState.entries(UserFacingMapState.java:77)
	at org.apache.flink.Reproducer$FailingMapWithState.open(Reproducer.java:78)
	at org.apache.flink.api.common.functions.util.FunctionUtils.openFunction(FunctionUtils.java:36)
	at org.apache.flink.streaming.api.operators.AbstractUdfStreamOperator.open(AbstractUdfStreamOperator.java:112)
	at org.apache.flink.streaming.runtime.tasks.StreamTask.openAllOperators(StreamTask.java:376)
	at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:252)
	at org.apache.flink.runtime.taskmanager.Task.run(Task.java:670)
	at java.lang.Thread.run(Thread.java:745)

The reason is that the record is null, because backend.getCurrentKey() is null (not yet set) in AbstractRocksDBState.
This may also be the case for other RockDBState implementations.

You can find the reproducer here based on 1.3-SNAPSHOT (needed for the MapState) :
https://github.com/vpernin/flink-rocksdbstate-npe

The reproducer is a non sense application. There is no MapState with TTL or expiration yet, so the goal is to try to shrink or expire the state at some interval.
This could be done by iterating over the entries of the state and removing some of them.

This could probably not be done in the open() method of a rich function.
I also tried to implement CheckpointListener and to access the state content in notifyCheckpointComplete() method, but it fails to, I guess due to the asynchronous nature of the checkpoint.

Issue Links

• links to: GitHub Pull Request #3545