[GitHub] [incubator-pegasus] levy5307 edited a comment on pull request #739: feat: implement value_schema_manager::get_value_schema

[GitBox <gi...@apache.org>]

levy5307 edited a comment on pull request #739:
URL: https://github.com/apache/incubator-pegasus/pull/739#issuecomment-851350250


   > The old `value_schema` is a table level concept defined in `data_version` in meta column family. Now, `value_schema` version 2 updates it, `value_schema` becomes a value level concept, a table is permitted having different value schema. However, it will raise two problems.
   > The first problem is the compatibility problem. New server version won't be downgraded because the old server can not figure out value_schema version 2 data. I think it is okay for new server can not downgrade, but our recent releases are almost all not-downgraded, should we merge this commit into master branch?
   > The second problem is the `data_version` in meta cf. This value is actually useless for new server, but it can not be removed for version0 and version1, would you have any solution to remove this value in future?
   
   I don't think so. Because value_schema version 2 will not updates data version in meta column family. It only reads from it.


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