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From Adrian McCague <Adrian.McCa...@zopa.com>
Subject RE: Streams + RocksDB + Avro
Date Wed, 15 Mar 2017 15:11:50 GMT
Hi Damian,

That is the SerDe we are using, agreed that looks like a good modification to make here for
a state store version. 
I would add that it is a good idea to include the record type as well since an edit of the
topology arrangement could still lead to issues down the line.

Thank you for your response, I will create a JIRA in due course

-----Original Message-----
From: Damian Guy [mailto:damian.guy@gmail.com] 
Sent: 15 March 2017 15:00
To: users@kafka.apache.org
Subject: Re: Streams + RocksDB + Avro

Hi Adrian,

The state store names are local names hence don't have the applicationId prefix, i.e., they
are laid out on disk like so:
/state.dir/applicationId/task/state-store-name. Their corresponding change-logs are prefixed
with the applicationId.

However, i can see in the case of the schema-registry that this would cause an issue as it
will use the state-store name when serializing and deserializing the keys and values.

Which Avro Serde are you using?

There is an example serde here:

You could potentially use something like this, but on line 57 prefix the topic name with the
applicationId (if it doesn't already have it).

Would you mind raising a JIRA for this? It seems like an issue other people are yet to encounter.


On Wed, 15 Mar 2017 at 13:05 Adrian McCague <Adrian.McCague@zopa.com> wrote:

> Hi all,
> We are getting collisions with subject names in our schema registry 
> due to state stores that are holding Avro events:
> "KSTREAM-JOINOTHER-0000000007-store-value",
>   "KSTREAM-JOINOTHER-0000000006-store-value",
>   "KSTREAM-JOINOTHER-0000000005-store-value",
>   "KSTREAM-OUTEROTHER-0000000005-store-value",
>   "KSTREAM-OUTEROTHER-0000000006-store-value",
>   "KSTREAM-JOINTHIS-0000000005-store-value",
>   "KSTREAM-JOINTHIS-0000000004-store-value",
>   "KSTREAM-JOINTHIS-0000000006-store-value",
> As you can see these are not prepended by their app id so any 
> similarly constructed topology in another Streams application, that 
> has different events will lead to conflicting schemas. Is this a bug, 
> intended or user error?
> I can see an advantage of the schema registry getting involved here 
> but not if this happens, I see a few work arounds but unsure if any 
> are recommended or there is something I have missed:
>   1.  Use an ObjectSerde / Serializable (though then lose the Avro 
> compatibility goodness)
>   2.  Create a modified SpecificAvroSerde that includes the schema 
> with each message
>   3.  Anyway to influence the subject name?
>   4.  Some form of local persistent schema registry for this purpose
> I am not sure if anything changed with how Serdes were passed to 
> RocksDB - I intend to deepdive into the source later at my next opportunity.
> I did notice non avro messages in our topologies started throwing 
> exceptions (not instances of SpecificRecord) since we moved to 
> so I suspect there was a plain Object serializer and now they 
> use the topology defaults if you do not supply a serde.
> Thanks
> Adrian
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