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Subject [GitHub] [flink] carp84 commented on issue #8069: [FLINK-12045] [core, State Backends] Support force migration between incompatible state schemas/serializers
Date Thu, 11 Apr 2019 07:48:53 GMT
carp84 commented on issue #8069: [FLINK-12045] [core, State Backends] Support force migration
between incompatible state schemas/serializers
URL: https://github.com/apache/flink/pull/8069#issuecomment-482006706
 
 
   After some offline discussion, @tzulitai pointed out that currently there are actually
2 cases with different semantic when serializer is marked as `INCOMPATIBLE`:
   1. The serializer has no idea whether or not the new serializer is compatible or not, e.g.
when the new serializer is a completely new class.
   2. The serializer really knows it is not compatible, e.g. in `PojoSerializer`, some field’s
type has changed.
   
   And we should only allow force migration for the 1st case since the 2nd will always fail.

   
   So we plan to split the whole work into two phases:
   1. Introduce a "UNKNOWN" type in `TypeSerializerSchemaCompatibility.Type` and respect this
`UNKNOWN` type for force migration, which will be implemented here.
   2. Go through all built-in serializers, to check which places we should return `UNKNOWN`
instead of `INCOMPATIBLE`, which will be implemented in a separated PR.
   
   Will update codes to reflect the above decision.

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