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From tzulitai <...@git.apache.org>
Subject [GitHub] flink pull request #6235: [FLINK-9377] [core] Remove serializers from checkp...
Date Mon, 02 Jul 2018 06:26:32 GMT
GitHub user tzulitai opened a pull request:

    https://github.com/apache/flink/pull/6235

    [FLINK-9377] [core] Remove serializers from checkpointed state meta infos

    ## What is the purpose of the change
    
    This PR is the first step towards a smoother state evolution experience.
    It removes the behavior of writing serializers in checkpointed state meta infos (using
Java serialization) and relying on them to be deserializable at restore time.
    Instead, the configuration snapshots of serializers now double as a factory for creating
the restore serializer, solidifying it as the single source of truth of information about
the previous serializer of state.
    
    With this change:
    - Checkpoints / savepoints move towards being Java serialization-free
    - The availability of the restore serializer, is basically determined at compile time
    - Potentially resolves caveats with macro-generated Scala serializers which typically
have anonymous classnames which are easily susceptible to changes, which blocks successful
savepoint restores due to how Java serialization works.
    - In conclusion: the written configuration snapshot is now the single point of entry for
obtaining a serializer for previous state. The user is only required to guarantee that the
configuration snapshot's classname remains constant for the restore to proceed.
    
    This PR is only a WIP which only includes extending the `TypeSerializerConfigSnapshot`
interface to include a `restoreSerializer` method, as well as the methods interplay in the
state backends after removing serializers from checkpointed state meta infos.
    
    This PR does **NOT** include:
    - Proper implementation of the new `restoreSerializer` method on all serializers.
    - Tests for snapshotting, restoring, and migrating serializers and their interplay in
the state backends.
    
    Because of this, it is expected that existing tests will fail.
    Follow-up PRs will be opened for the above mentioned missing parts.
    
    ## Brief change log
    
    - 5fc4a36 Add a `restoreSerializer` method to the `TypeSerializerConfigSnapshot` interface
    
    The method still has a dummy base implementation, because this PR doesn't yet properly
implement the method for all serializers. Once that is accomplished, the base implementation
should be removed.
    
    - 661eb6d Remove the "fallback" serializer option from `CompatibilityResult`
    
    That option was available in the past to allow users to have a safety path for state conversion,
in case their previous serializer cannot be deserialized due to any reason blocked by Java
serialization. Since now we use the config snapshot as the restore serializer factory, it
is guaranteed that the restore serializer is always available in case conversion is required,
and therefore voids the need for the "fallback" serializer option.
    
    - c91d045 Deprecates any utility methods that still have the behaviour of writing serializers
in checkpoints
    
    - e09f914 Introduces the `BackwardsCompatibleConfigSnapshot` class
    
    The BackwardsCompatibleConfigSnapshot is a wrapper, dummy config
    snapshot which wraps an actual config snapshot, as well as a
    pre-existing serializer instance.
    
    In previous versions, since the config snapshot wasn't a serializer
    factory but simply a container for serializer parameters, previous
    serializers didn't necessarily have config snapshots that are capable of
    correctly creating a correct corresponding restore serializer.
    
    In this case, since previous serializers still have serializers written
    in the checkpoint, the backwards compatible solution would be to wrap
    the written serializer and the config snapshot within the
    BackwardsCompatibleConfigSnapshot dummy. When attempting to restore the
    serializer, the wrapped serializer instance is returned instead of
    actually calling the restoreSerializer method of the wrapped config
    snapshot.
    
    - da84665 the actual removal of serializers from checkpointed state meta info
    
    ## Verifying this change
    
    This PR is a WIP preview, and tests is expected to fail due to reasons mentioned in the
description.
    
    ## Does this pull request potentially affect one of the following parts:
    
      - Dependencies (does it add or upgrade a dependency): (yes / **no**)
      - The public API, i.e., is any changed class annotated with `@Public(Evolving)`: (**yes**
/ no)
      - The serializers: (**yes** / no / don't know)
      - The runtime per-record code paths (performance sensitive): (yes / **no** / don't know)
      - Anything that affects deployment or recovery: JobManager (and its components), Checkpointing,
Yarn/Mesos, ZooKeeper: (**yes** / no / don't know)
      - The S3 file system connector: (yes / **no** / don't know)
    
    ## Documentation
    
      - Does this pull request introduce a new feature? (yes / **no**)
      - If yes, how is the feature documented? (not applicable / docs / **JavaDocs** / not
documented)


You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/tzulitai/flink FLINK-9377

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/flink/pull/6235.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #6235
    
----
commit 5fc4a36a144c3f8f22be7e21a4e542d3042d10b1
Author: Tzu-Li (Gordon) Tai <tzulitai@...>
Date:   2018-06-13T11:43:53Z

    [FLINK-9377] [core] (part 1) Extend TypeSerializerConfigSnapshot as a factory for restoring
serializers
    
    This commit is the first step towards removing serializers from
    checkpointed state meta info and making Flink checkpoints Java
    serialization free.
    
    Instead of writing serializers in checkpoints, and trying to read that
    to obtain a restore serializer at restore time, we aim to only write the
    config snapshot as the single source of truth and use it as a factory to
    create a restore serializer.
    
    This commit adds the method and signatures to the
    TypeSerializerConfigSnapshot interface. Use of the method, as well as
    properly implementing the method for all serializers, will be
    implemented in follow-up commits.

commit 661eb6d34da450ed096a77f166a4cc62ce3efdba
Author: Tzu-Li (Gordon) Tai <tzulitai@...>
Date:   2018-06-14T09:52:06Z

    [FLINK-9377] [core] (part 2) Remove fallback deserializer option from CompatibilityResult
    
    Now that the config snapshot is used as a factory for the restore
    serializer, it should be guaranteed that a restore serializer is always
    available. This removes the need for the user to provide a "fallback"
    convert serializer in the case where a migration is required.

commit c91d045c5eb6e355981e4edaa6d1a0d48e5d4a5e
Author: Tzu-Li (Gordon) Tai <tzulitai@...>
Date:   2018-06-14T14:41:45Z

    [FLINK-9377] [core] (part 3) Deprecate TypeSerializerSerializationUtil
    
    This commit deprecates all utility methods and classes related to
    serializing serializers. All methods that will still be in use, i.e.
    writing config snapshots, are now moved to a separate new
    TypeSerializerConfigSnapshotSerializationUtil class.

commit e09f91469fb6c86f5d2f05b78a9db3d9af8cce87
Author: Tzu-Li (Gordon) Tai <tzulitai@...>
Date:   2018-06-18T14:24:08Z

    [FLINK-9377] [core] (part 4) Introduce BackwardsCompatibleConfigSnapshot
    
    The BackwardsCompatibleConfigSnapshot is a wrapper, dummy config
    snapshot which wraps an actual config snapshot, as well as a
    pre-existing serializer instance.
    
    In previous versions, since the config snapshot wasn't a serializer
    factory but simply a container for serializer parameters, previous
    serializers didn't necessarily have config snapshots that are capable of
    correctly creating a correct corresponding restore serializer.
    
    In this case, since previous serializers still have serializers written
    in the checkpoint, the backwards compatible solution would be to wrap
    the written serializer and the config snapshot within the
    BackwardsCompatibleConfigSnapshot dummy. When attempting to restore the
    serializer, the wrapped serializer instance is returned instead of
    actually calling the restoreSerializer method of the wrapped config
    snapshot.

commit da84665a9b101a803f7446210afc34bbd4a71703
Author: Tzu-Li (Gordon) Tai <tzulitai@...>
Date:   2018-07-02T03:45:20Z

    [FLINK-9377] [core] (part 5) Remove serializers from checkpoint state meta infos
    
    This commit officially removes the behaviour of writing serializers in
    the state meta info of keyed state, operator state, and timers state.
    This affects the serialization formats of the
    KeyedBackendSerializationProxy, OperatorBackendSerializationProxy, and
    InternalTimerServiceSerializationProxy, and therefore their versions are
    all upticked.

----


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