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From "Federico D'Ambrosio" <federico.dambro...@smartlab.ws>
Subject Re: How to deal with java.lang.IllegalStateException: Could not initialize keyed state backend after a code update
Date Tue, 28 Nov 2017 15:20:27 GMT
Hi Gordon,

explicitly specifying the serialversionuid did the job, thank you! The
failing task was latest_time -> (cassandra-map -> Sink:
cassandra-active-sink, map_active_stream, map_history_stream) like the

val events = keyedstream


with cassandra-map, map_history_stream and map_active_stream, stateless map
So, I guess the culprit was either the window/maxBy operator or the
cassandra sink. I guess the window/maxBy operator, since the initialization
of a keyed state is specified.
I'm attaching the complete log.


2017-11-28 15:32 GMT+01:00 Tzu-Li (Gordon) Tai <tzulitai@apache.org>:

> Hi Federico,
> It seems like the state cannot be restored because the class of the state
> type (i.e., Event) had been modified since the savepoint, and therefore has
> a conflicting serialVersionUID with whatever it is in the savepoint.
> This can happen if Java serialization is used for some part of your state,
> and the class of the written data was modified while a fixed
> serialVersionUID was not explicitly specified for that class.
> To avoid this, you should explicitly set a serialVersionUID for the Event
> class.
> You can actually also do that now without losing state while also
> incorporating the modifications you were trying to do for your updated job.
> Explicitly declare the serialVersionUID of the Event class to what is was
> before your modifications (i.e., 8728793377941765980, according to your
> error log).
> One side question: are you experiencing this restore failure for one of
> your custom operator states, or is this failing state part of some Flink
> built-in operator / connector?
> I’m asking just to have an idea of which Flink built-in operator /
> connectors still use Java serialization for user state; ideally we would
> want that to be completed removed in the future.
> Cheers,
> Gordon
> On 28 November 2017 at 10:02:19 PM, Federico D'Ambrosio (
> federico.dambrosio@smartlab.ws) wrote:
> Hi,
> I recently had to do a code update of a long running Flink Stream job
> (1.3.2) and on the restart from the savepoint I had to deal with:
> java.lang.IllegalStateException: Could not initialize keyed state backend.
> Caused by: java.io.InvalidClassException: lab.vardata.events.Event; local
> class incompatible: stream classdesc serial
> VersionUID = 8728793377341765980, local class serialVersionUID =
> -4253404384162522764
> because I have changed a method used to convert the Event to a Cassandra
> writable Tuple (in particular, I changed the return type from Tuple10 to
> Tuple11, after adding a field). I reverted those changes back since it
> wasn't much of a problem per se.
> Now, I understand the root cause of this issue and I wanted to ask if
> there are any "best practices" to prevent this kind of issues, without
> losing the state of the job, because of restarting it from the very
> beginning.
> --
> Federico D'Ambrosio

Federico D'Ambrosio

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