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The intent is to make data returned by queries always conform to a single schema version, which is requested by the client. For CQL queries, for example, we want to use the same schema which was used to compile the query. The other node expects to receive data conforming to the requested schema. Interface on shard level accepts schema_ptr, across nodes we use table_schema_version UUID. To transfer schema_ptr across shards, we use global_schema_ptr. Because schema is identified with UUID across nodes, requestors must be prepared for being queried for the definition of the schema. They must hold a live schema_ptr around the request. This guarantees that schema_registry will always know about the requested version. This is not an issue because for queries the requestor needs to hold on to the schema anyway to be able to interpret the results. But care must be taken to always use the same schema version for making the request and parsing the results. Schema requesting across nodes is currently stubbed (throws runtime exception).