isidentical opened a new pull request, #3804:
URL: https://github.com/apache/arrow-datafusion/pull/3804
# Which issue does this PR close?
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Closes #3803.
# Rationale for this change
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This is something that arrow-rs already does very heavily, although they
also combine it with the unsafe array building APIs which this PR deliberately
avoids (reasoning is at the end).
It doesn't provide as much speed-up as the other optimizations for the
`regex_replace`, but it seems like a relatively straightforward change for a
not-so-bad gain (see benchmarks section). It is also the final optimization
candidate (at least localized to the `regex_replace` itself), if I am not
missing anything.
# What changes are included in this PR?
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Instead of rebuilding the string array from the iterator, we now build the
underlying array data by ourselves in which case we also have the ability to
leverage existing null buffers for the input. In the generic version, this
couldn't be done without recombining the underlying bitmaps of all the inputs
but since this is the specialized case we know for a fact that the only array
input is the `strings` (the first argument).
# Are there any user-facing changes?
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This is an optimization.
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# Benchmarks
As expected, there is no speed-up (or slowdowns, which I guess is
noteworthy) in cases where the input array is very dense with data (low amount
of NULLs). But depending on the input's data density, we see an average
speed-up of %20.
| | master | this pr | this pr (unsafe) |
speed-up |
|----------------------------|--------|---------|------------------|------------------------------------------------------|
| %100 null & %0 data | 0.121 | 0.088 | 0.071 | 1.38x
against this PR (1.71x against unsafe version) |
| %80 null & %20 data | 0.489 | 0.396 | 0.347 | 1.23x
against this PR (1.40x against unsafe version) |
| %50 null & %50 data | 0.741 | 0.640 | 0.619 | 1.15x
against this PR (1.20x against unsafe version) |
| data > null (80-20, 100-0) | 1.104 | 1.101 | 1.067 | No
change (<=%3, within noise) |
(Built with the release mode, for a variation of the query/dataset in my
[example PR](https://github.com/isidentical/arrow-datafusion/pull/3)).
I have also included a column which indicates the speed-ups when we use the
unsafe version but I am not so sure if it makes sense to increase the number of
'unsafe' spots in datafusion for a not-so-crazy speed-up (even if that from the
soundness perspective it is safe). I'd be happy to also change my PR to include
the unsafe version ([which looks like
this](https://github.com/isidentical/arrow-datafusion/pull/3)) if it is not
that bad.
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