[GitHub] [beam] lukecwik edited a comment on pull request #13069: [BEAM-10475] Add a well-known coder for ShardedKey in Java/Python SDK

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lukecwik edited a comment on pull request #13069:
URL: https://github.com/apache/beam/pull/13069#issuecomment-707911475


   > On empty key vs. marker, sorry for going back and forth--let's settle this before you change the code again.
   > 
   > Taking a step back, the question we want to answer is "do all ShardedKeys have a shard id" or is the shard id optional. If the former, I think representing it as a `(bytes, K)` tuple makes sense, but if we ever want to talk about "not having" a shard id than it should, logically, be `(Optional[bytes], K)` and we should use an explicit bit rather than have a "special" value of bytes that means "not there".
   
   Since we expect ShardedKey to be produced by the runner we don't expect the SDK/user to care so making it required simplifies user & SDK code. The runner is the only one that may care to differentiate unsharded vs sharded and can use any representation it wants to do so (e.g. by encoding Optional[bytes] into the bytes blob). The runners type doesn't have to match the user/SDK type.


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