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Downgrades the db specified in the connection config to a schema version.
mlmd.metadata_store.downgrade_schema( config, downgrade_to_schema_version )
downgrade_to_schema_version is greater or equals to zero and less than
the current library's schema version, it runs a downgrade transaction to
revert the db schema and migrate the data. The update is transactional, and
any failure will cause a full rollback of the downgrade. Once the downgrade
is done, the user needs to use the older version of the library to connect to
config: a metadata_store_pb2.ConnectionConfig having the connection params
downgrade_to_schema_version: downgrades the given database to a specific version. For v0.13.2 release, the schema_version is 0. For 0.14.0 and 0.15.0 release, the schema_version is 4. More details are described in g3doc/get_start#upgrade_mlmd_library
InvalidArgumentError: if the
downgrade_to_schema_versionis not given or it is negative or greater than the library version.
RuntimeError: if the downgrade is not finished, return detailed error.