prtkgaur opened a new pull request, #51250: URL: https://github.com/apache/arrow/pull/51250
### Rationale for this change The miniblocks of a DELTA_BINARY_PACKED block are packed back to back with no padding between them, so a run of miniblocks that share a bit width is bit-identical to a single longer run at that width. `GetInternal` calls the bit unpacker once per miniblock all the same, which with the default geometry is one call per 32 values -- at narrow widths, mostly per-call setup. ### What changes are included in this PR? A look-ahead over the block's stored bit widths, in a small private helper, reports how many of the following miniblocks may be folded into the current unpack call, so a run of four asks the unpacker for 128 values instead of 32. A miniblock joins the run only when its stored width *equals* the current `delta_bit_width_`, which `InitMiniBlock` has already validated, and the run also stops at the end of the block and at what the caller has room for. ### Are these changes tested? A new typed test covers the width patterns that decide where a run starts and stops, and the fixture's read batch sizes gain one that stops partway through a coalesced run, so the existing round trips cover it too. Three mutations of the implementation -- ignoring the neighbour's width, ignoring the caller's room, and failing to advance the block cursor -- each turn the new test red. ### Benchmark Same setup as the previous PR: AWS Graviton4, GCC 11.5, `Release`, one core, 9 repetitions, medians, 65,536 values, both arms built and measured in one sitting. The two `Fixed` arms are the `delta_bit_width_ == 0` path, which has no unpack call to coalesce. | benchmark | previous commit | this PR | | vs. main | |---|--:|--:|--:|--:| | `Decode_Int32_Narrow` | 78.11 us | 58.61 us | **1.33x** | **1.70x** | | `Decode_Int32_Wide` | 80.79 us | 65.08 us | **1.24x** | **1.57x** | | `Decode_Int64_Narrow` | 64.41 us | 55.08 us | **1.17x** | **1.49x** | | `Decode_Int64_Wide` | 308.65 us | 301.60 us | 1.02x | 1.06x | | `Decode_Int32_Fixed` | 19.75 us | 20.31 us | 0.97x | 0.97x | | `Decode_Int64_Fixed` | 32.20 us | 31.74 us | 1.01x | 0.97x | ### Are there any user-facing changes? No. No API change, no format change, and decoded values are identical. **This PR includes breaking changes to public APIs.** (If there are any breaking changes to public APIs, please explain which changes are breaking. If not, you can remove this.) **This PR contains a "Critical Fix".** (If the changes fix either (a) a security vulnerability, (b) a bug that caused incorrect or invalid data to be produced, or (c) a bug that causes a crash (even when the API contract is upheld), please provide explanation. If not, you can remove this.) -- 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]
