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Scott Carey commented on AVRO-1335: ----------------------------------- Thanks for the clarification. Is it safe to summarize the issue as "C++ should support field default values"? Or are there other things that are also preventing bidirectional schema evolution use cases besides default values? I cannot provide a time-frame for this, the volunteers who build and maintain the C++ Avro code may have more information. > ResolvingDecoder should provide bidirectional compatibility between different > version of schemas > ------------------------------------------------------------------------------------------------ > > Key: AVRO-1335 > URL: https://issues.apache.org/jira/browse/AVRO-1335 > Project: Avro > Issue Type: Improvement > Components: c++ > Affects Versions: 1.7.4 > Reporter: Bin Guo > > We found that resolvingDecoder could not provide bidirectional compatibility > between different version of schemas. > Especially for records, for example: > {code:title=First schema} > { > "type": "record", > "name": "TestRecord", > "fields": [ > { > "name": "MyData", > "type": { > "type": "record", > "name": "SubData", > "fields": [ > { > "name": "Version1", > "type": "string" > } > ] > } > }, > { > "name": "OtherData", > "type": "string" > } > ] > } > {code} > {code:title=Second schema} > { > "type": "record", > "name": "TestRecord", > "fields": [ > { > "name": "MyData", > "type": { > "type": "record", > "name": "SubData", > "fields": [ > { > "name": "Version1", > "type": "string" > }, > { > "name": "Version2", > "type": "string" > } > ] > } > }, > { > "name": "OtherData", > "type": "string" > } > ] > } > {code} > Say, node A knows only the first schema and node B knows the second schema, > and the second schema has more fields. > Any data generated by node B can be resolved by first schema 'cause the > additional field is marked as skipped. > But data generated by node A can not be resolved by second schema and throws > an exception *"Don't know how to handle excess fields for reader."* > This is because data is resolved exactly according to the auto-generated > codec_traits which trying to read the excess field. > The problem is we just can not only ignore the excess field in record, since > the data after the troublesome record also needs to be resolved. > Actually this problem stucked us for a very long time. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira