Rich-T-kid opened a new pull request, #11296: URL: https://github.com/apache/arrow-rs/pull/11296
Dictionary encoding re-encodes O(NDV) values on every convert_columns call. In global-dictionary workloads the same values Arc is reused across batches, so that work is redundant. Codec::Dictionary now stores a Mutex<Option<(arc_ptr, Arc<Rows>)>>. When the values Arc pointer matches the cached pointer the pre-encoded Rows are reused without re-encoding. The Arc<Rows> wrapper lets the Encoder share ownership of the cached buffer without copying. At NDV=10K this closes the dict/UTF-8 gap from ~30 µs to ~24 µs (vs ~23 µs for UTF-8). Above NDV=200K the remaining bottleneck is N random accesses into an encoded-values buffer that exceeds L3 capacity. # 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 #NNN. # 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. --> # 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. --> # 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. --> # 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]
