Hi Robert,

I found an potientally blocking issue in RC1 that I would like to bring up for 
debate. In [FLINK-5602], Ufuk found a NPE that happened during the first 
checkpoint after migrating a job from Flink 1.1 to 1.2. I looked into this and 
found that the cause of this problem is the absense of namespace serializers in 
Flink 1.1 checkpoints. Flink 1.2 always makes all serializers part of the 
checkpoint and therefore a precondition to checkpointing fails if a checkpoint 
runs before the user code is delivering the namespace serializer. This is a 
race condition that (depending on the user code) could fail almost 
deterministcally in some situations (e.g. user is registering the state rather 
late). The consequence is that checkpointing (and the whole job) fails in this 
scenario and potentially prevents user from upgrading to 1.2. I have a open PR 
#3200 that is fixing this problem.

Best,
Stefan

> Am 24.01.2017 um 15:03 schrieb Robert Metzger <rmetz...@apache.org>:
> 
> Dear Flink community,
> 
> Please vote on releasing the following candidate as Apache Flink version
> 1.2.0.
> 
> The commit to be voted on:
> 1bca1208 (*http://git-wip-us.apache.org/repos/asf/flink/commit/1bca1208
> <http://git-wip-us.apache.org/repos/asf/flink/commit/1bca1208>*)
> 
> Branch:
> release-1.2.0-rc1
> (https://git1-us-west.apache.org/repos/asf/flink/repo?p=
> flink.git;a=shortlog;h=refs/heads/release-1.2.0-rc1)
> 
> The release artifacts to be voted on can be found at:
> *http://people.apache.org/~rmetzger/flink-1.2.0-rc1/
> <http://people.apache.org/~rmetzger/flink-1.2.0-rc1/>*
> 
> The release artifacts are signed with the key with fingerprint D9839159:
> http://www.apache.org/dist/flink/KEYS
> 
> The staging repository for this release can be found at:
> https://repository.apache.org/content/repositories/orgapacheflink-1112
> 
> -------------------------------------------------------------
> 
> The vote ends in three days (3 pm CET | Friday, January 27, 2017)
> 
> Please test the release rather now than on Friday morning, to be able to
> cancel it as early as possible.
> For making the testing easier, I've created this document to track what has
> already been tested and what needs to be tested:
> https://docs.google.com/document/d/1MX-8l9RrLly3UmZMODHBnuZUrK_n-DGIBLjFKyCrTAs/edit?usp=sharing
> Feel free to add more tests or change existing ones.
> 
> [ ] +1 Release this package as Apache Flink 1.2.0
> [ ] -1 Do not release this package, because ...

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