Hi devs, I would like to open a discussion to remove the long deprecated (@PublicEvolving) TypeSerializerConfigSnapshot class [1] and the related code.
The motivation behind this move is two fold. One reason is that it complicates our code base unnecessarily and creates confusion on how to actually implement custom serializers. The immediate reason is that I wanted to clean up Flink's configuration stack a bit and refactor the ExecutionConfig class [2]. This refactor would keep the API compatibility of the ExecutionConfig, but it would break savepoint compatibility with snapshots written with some of the old serializers, which had ExecutionConfig as a field and were serialized in the snapshot. This issue has been resolved by the introduction of TypeSerializerSnapshot in Flink 1.7 [3], where serializers are no longer part of the snapshot. TypeSerializerConfigSnapshot has been deprecated and no longer used by built-in serializers since Flink 1.8 [4] and [5]. Users were encouraged to migrate to TypeSerializerSnapshot since then with their own custom serializers. That has been plenty of time for the migration. This proposal would have the following impact for the users: 1. we would drop support for recovery from savepoints taken with Flink < 1.7.0 for all built in types serializers 2. we would drop support for recovery from savepoints taken with Flink < 1.8.0 for built in kryo serializers 3. we would drop support for recovery from savepoints taken with Flink < 1.17 for custom serializers using deprecated TypeSerializerConfigSnapshot 1. and 2. would have a simple migration path. Users migrating from those old savepoints would have to first start his job using a Flink version from the [1.8, 1.16] range, and take a new savepoint that would be compatible with Flink 1.17. 3. This is a bit more problematic, because users would have to first migrate their own custom serializers to use TypeSerializerSnapshot (using a Flink version from the [1.8, 1.16]), take a savepoint, and only then migrate to Flink 1.17. However users had already 4 years to migrate, which in my opinion has been plenty of time to do so. As a side effect, we could also drop support for some of the legacy metadata serializers from LegacyStateMetaInfoReaders and potentially other places that we are keeping for the sake of compatibility with old savepoints. What do you think? Best, Piotrek [1] https://nightlies.apache.org/flink/flink-docs-master/api/java/org/apache/flink/api/common/typeutils/TypeSerializerConfigSnapshot.html [2] https://issues.apache.org/jira/browse/FLINK-29379 [3] https://issues.apache.org/jira/browse/FLINK-9377 [4] https://issues.apache.org/jira/browse/FLINK-9376 [5] https://issues.apache.org/jira/browse/FLINK-11323
