Persist: clarify reduced semantics to refer only to spine structure
#33508
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bkirwi
approved these changes
Sep 11, 2025
| // parts can be cleaned up by compaction, which we intentionally ignore here to | ||
| // avoid repeatedly injecting empty batches when only structure-level compaction | ||
| // remains. | ||
| self.spine_batches().count() < 2 |
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Thinking about this again from scratch, it feels like the "real criteria" for whether there's any real work to do would be whether there are <2 runs, like we do in is_compact.
Anyways I think this is probably an improvement, but consider that change pre-approved if it tests well!
The exert function is called exclusively by the catalog force compaction code path. In the case that there was only one spine batch with multiple hollow batches, the exert function would incorrectly introduce empty SpineBatches. The behavior of the `reduced` function was always using the number of HollowBatches as a proxy for the structural shape of the spine. With incremental compaction, there might be only one run with a number of empty HollowBatches. This is totally legal, and not a reason to try and force structural merges.
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The exert function is called exclusively by the catalog force compaction code path. In the case that there was only one spine batch with multiple hollow batches, the exert function would incorrectly introduce empty SpineBatches. The behavior of the
reducedfunction was always using the number of HollowBatches as a proxy for the structural shape of the spine. With incremental compaction, there might be only one run with a number of empty HollowBatches. This is totally legal, and not a reason to try and force structural merges.Motivation
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Checklist
$T ⇔ Proto$Tmapping (possibly in a backwards-incompatible way), then it is tagged with aT-protolabel.