damccorm opened a new issue, #20509: URL: https://github.com/apache/beam/issues/20509
### Problem/Status The schema proto has an [encoding_position field](https://github.com/apache/beam/blob/2c619c81082839e054f16efee9311b9f74b6e436/model/pipeline/src/main/proto/schema.proto#L55) that is currently unused in every row coder implementation. The intention of this field is that it indicates an alternative order for the fields to be encoded in by [beam:coder:row:v1 implementations](https://github.com/apache/beam/blob/1e60f383fb39b9ff8d44edcbe5357da4c1e52378/model/pipeline/src/main/proto/beam_runner_api.proto#L937-L990). Currently all the implementations ignore this field, and always encode the fields in the order that they appear in the schema. ### Motivation The idea with the encoding position is that it will give runners a way to enforce schema compatibility (BEAM-9502), by re-ordering the way fields are encoded when the schema changes between two job submissions. Schema changes could be due to fields re-ordering, or field additions/deletions. ### Code pointers The Python beam:coder:row:v1 implementation lives in [row_coder.py](https://github.com/apache/beam/blob/master/sdks/python/apache_beam/coders/row_coder.py) The Java implementation is a little more complicated, distributed between [SchemaCoder](https://github.com/apache/beam/blob/master/sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/SchemaCoder.java), [RowCoder](https://github.com/apache/beam/blob/master/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/RowCoder.java), and [RowCoderGenerator](https://github.com/apache/beam/blob/master/sdks/java/core/src/main/java/org/apache/beam/sdk/coders/RowCoderGenerator.java). RowCoderGenerator contains the code relevant to this jira - it uses bytebuddy to generate Java code for the coder. We need it to generate code that puts fields in the order specified by encoding_position. ### Testing Python and Java implementations should be tested with unit tests ([RowCoderTest](https://github.com/apache/beam/blob/master/sdks/java/core/src/test/java/org/apache/beam/sdk/coders/RowCoderTest.java), [row_coder_test](https://github.com/apache/beam/blob/master/sdks/python/apache_beam/coders/row_coder_test.py)). We should also test them for compatibility by adding test cases that exercise the encoding_position in [standard_coders.yaml](https://github.com/apache/beam/blob/master/model/fn-execution/src/main/resources/org/apache/beam/model/fnexecution/v1/standard_coders.yaml). These tests will be executed by [CommonCoderTest](https://github.com/apache/beam/blob/master/runners/core-construction-java/src/test/java/org/apache/beam/runners/core/construction/CommonCoderTest.java) and [standard_coders_test](https://github.com/apache/beam/blob/master/sdks/python/apache_beam/coders/standard_coders_test.py). There's some example code for generating a new test case [here](https://github.com/apac he/beam/blob/master/model/fn-execution/src/main/resources/org/apache/beam/model/fnexecution/v1/standard_coders.yaml#L387-L400). Imported from Jira [BEAM-10277](https://issues.apache.org/jira/browse/BEAM-10277). Original Jira may contain additional context. Reported by: bhulette. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
