[GitHub] [arrow-rs] jhorstmann opened a new issue #397: Optimize MutableArrayData::extend for null buffers

[GitBox <gi...@apache.org>]

jhorstmann opened a new issue #397:
URL: https://github.com/apache/arrow-rs/issues/397


   In one of our benchmarks the `concat` kernel was identified as a big performance bottleneck while sorting, specifically the closures inside `build_extend_null_bits`. The logic in there currently sets individual bits and also contains a branch for every bit
   
   ```
   if bit_util::get_bit(...) {
       bit_util::set_bit(...);
   }
   ```
   
   I think it should be possible to rewrite this to set multiple bits at the same time and remove most of the branch overhead. The general idea would look like this:
   
   - append individual bits until the destination buffer starts at a byte offset
   - start a BitChunk iterator on the source buffer and then append u8 or u64 at a time
   - append the remainder u8 at a time
   
   Similar logic would apply to setting all bits to valid, appending chunks of u8::MAX or u64::MAX at a time.
   
   The `get_bit` / `set_bit` functions themselves could probably also be speed up a little, I think on modern processors calculating the bit masks instead of using a lookup table should be faster. But after the above changes, those functions would no longer be used in the hot path.


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[GitHub] [arrow-rs] alamb closed issue #397: Optimize MutableArrayData::extend for null buffers

[GitBox <gi...@apache.org>]

alamb closed issue #397:
URL: https://github.com/apache/arrow-rs/issues/397


   


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[GitHub] [arrow-rs] mathiaspeters-sig commented on issue #397: Optimize MutableArrayData::extend for null buffers

[GitBox <gi...@apache.org>]

mathiaspeters-sig commented on issue #397:
URL: https://github.com/apache/arrow-rs/issues/397#issuecomment-902529475


   Since I can't assign myself I'll comment instead: I'm starting to work on this now


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[GitHub] [arrow-rs] Dandandan commented on issue #397: Optimize MutableArrayData::extend for null buffers

[GitBox <gi...@apache.org>]

Dandandan commented on issue #397:
URL: https://github.com/apache/arrow-rs/issues/397#issuecomment-902628995


   @mathiaspeters-sig 
   
   There might be some inspiration to use from the work in arrow2 by @jorgecarleitao , e.g. see https://github.com/jorgecarleitao/arrow2/pull/291


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