asubiotto opened a new pull request, #9940: URL: https://github.com/apache/arrow-rs/pull/9940
# Which issue does this PR close? <!-- We generally require a GitHub issue to be filed for all bug fixes and enhancements and this helps us generate change logs for our releases. You can link an issue to this PR using the GitHub syntax. --> - Closes #9939 # Rationale for this change <!-- Why are you proposing this change? If this is already explained clearly in the issue then this section is not needed. Explaining clearly why changes are proposed helps reviewers understand your changes and offer better suggestions for fixes. --> interleave_dictionaries checks if input dictionaries should be merged/GCed, but should_merge_dictionary_values has limited type support due to the bytes interning it does. For other types and in the general fallback case where the heuristic fails, interleave_fallback_dictionary concatenates all the values slices together, resulting in a lot of bloat in cases where the interleave selection is minimal. This happens a lot e.g. in datafusion on a multi-partition sort on a dictionary column. # What changes are included in this PR? <!-- There is no need to duplicate the description in the issue here but it is sometimes worth providing a summary of the individual changes in this PR. --> This commit improves these cases by introducing a heuristic to check interleave index coverage assuming uniform value selection. When coverage is less than the number of values, interleave_fallback_dictionary now performs a `take` on the value slices in order to reduce output size bloat. On a real-world datafusion sort that motivated this change, I saw runtime drop from 20 minutes to 7 minutes. The heuristic allows us to avoid a microbenchmark regression. # Are these changes tested? <!-- We typically require tests for all PRs in order to: 1. Prevent the code from being accidentally broken by subsequent changes 2. Serve as another way to document the expected behavior of the code If tests are not included in your PR, please explain why (for example, are they covered by existing tests)? If this PR claims a performance improvement, please include evidence such as benchmark results. --> Yes, by existing tests and some new tests exercising this path specifically. # Are there any user-facing changes? <!-- If there are user-facing changes then we may require documentation to be updated before approving the PR. If there are any breaking changes to public APIs, please call them out. --> -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
