lostluck opened a new issue, #22704:
URL: https://github.com/apache/beam/issues/22704

   ### What would you like to happen?
   
   The Go SDK's combiner lifting currently encodes keys twice for caching. 
First it encodes values into a hash function, and then it repeats it to get the 
[]byte for byte by byte comparisons in the cache.
   
   
https://github.com/apache/beam/blob/master/sdks/go/pkg/beam/core/runtime/exec/combine.go#L469
   
   
https://github.com/apache/beam/blob/master/sdks/go/pkg/beam/core/runtime/exec/combine.go#L483
   
   For expensive keys, this can become very expensive without additional 
caching schemes.
   
   Ideally this encoding happens once, instead of twice for each key being 
looked up.
   
   Note: Windowed byte equality is important to use for final lookups because 
that's the only way to ensure equivalence to runners. Beam Model GBKs use byte 
equality for keys as their basis.
   
   ### Issue Priority
   
   Priority: 2
   
   ### Issue Component
   
   Component: sdk-go


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