[GitHub] [arrow] jacques-n edited a comment on pull request #8214: ARROW-9965: [Java] Improve performance of BaseFixedWidthVector.setSafe by optimizing capacity calculations

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jacques-n edited a comment on pull request #8214:
URL: https://github.com/apache/arrow/pull/8214#issuecomment-696459730


   > I think there are two opportunities here - simply optimizing setSafe, which can be done by either specializing for the power-of-two size where possible, or by caching sizes (option 1/option 3); and considering a separate builder API that can also provide performance improvements, which I think can be considered separately.
   > 
   > As for whether to cache sizes (option 3) or optimize for power-of-two lengths only, I would prefer to cache sizes as it's more general and as shown here, faster in microbenchmarks. However there could ecosystem code that expects to be able to reallocate buffers manually - if so, this would be a breaking change, and so I'd rather take the smaller/guaranteed win.
   > 
   > (Option 4 is essentially inlining an optimized builder API into the benchmark, no?)
   
   I'm clearly missing something. Why doesn't item 2 when directly in the vector solve the same purpose as 1/3?


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