[GitHub] [arrow] jorgecarleitao edited a comment on pull request #9235: ARROW-11291: [Rust] Add extend to MutableBuffer (-25% for aritmetic, -97% for length)

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jorgecarleitao edited a comment on pull request #9235:
URL: https://github.com/apache/arrow/pull/9235#issuecomment-763898758


   I made a mistake in benchmarking and have to retract my statement. I am really sorry for the noise. :(
   
   I mistakenly updated the wrong part of the code before running the bench.
   
   @mbrubeck , even though there is a small difference between the the two extends in the benches that you added, when used in a non-trivial operation (`arithmetic`), `collect` is about +65% slower than using `extend_from_trusted_len_iter`.
   
   This hints that the `extend_trusted_len_iter` does have a significant benefit, if anything at helping the compiler optimize out some code.
   
   what I am using for the final benches:
   
   ```bash
   git checkout 7bb2f3c13f0e652b01e3fecbee0ae32ff094f3e6
   cargo bench --bench arithmetic_kernels -- "add 512"
   git checkout cdbbc6f9d81d37216dc158177405529988fa0279
   cargo bench --bench arithmetic_kernels -- "add 512"
   ```
   
   The difference in code is 
   
   ```rust
       let values = left
           .values()
           .iter()
           .zip(right.values().iter())
           .map(|(l, r)| op(*l, *r));
       let mut buffer = MutableBuffer::new(0);
       unsafe { buffer.extend_from_trusted_len_iter(values) };
   ```
   
   to 
   
   ```rust
       let buffer = left
           .values()
           .iter()
           .zip(right.values().iter())
           .map(|(l, r)| op(*l, *r))
           .collect();
   ```
   
   IMO this is interesting by itself.
   


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