Report the rank of each entry when scanning a rank index - #4563
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A rank index scan cannot currently tell a caller what rank each entry holds. A BY_RANK scan converts the rank range into a score range and then performs an ordinary by-value scan, so its entries are identical to those a BY_VALUE scan produces: the rank is consumed as a bound and never reported. The rank is stored in neither the entry key nor the entry value, and a rank index leaves the value empty. This adds RankScanBounds, an IndexScanBounds accepting BY_VALUE or BY_RANK together with an includeRankAsValue option that asks RankIndexMaintainer to report each entry's rank in the otherwise empty value. The rank lookup that the RANK record function already performed is reused: it needed a record only in order to evaluate the index key against it, so it is now keyed off the index key itself, which a scan already has in hand.
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normen662
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Please open an issue for the follow up work and add this here. |
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done #4608. |
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A scan of a rank index cannot currently tell a caller what rank each entry holds.
BY_RANKconverts the rank range into a score range and then performs an ordinary by-value scan, so its entries come back byte-for-byte identical to whatBY_VALUEyields — the rank is consumed as a bound and then discarded. It is stored in neither the entry key nor the entry value, and a rank index leaves the value empty. Anything that wants to project a rank, rather than merely filter on one, therefore has nothing to read.This adds
RankScanBounds, anIndexScanBoundsthat acceptsBY_VALUEorBY_RANKalong with anincludeRankAsValueoption askingRankIndexMaintainerto report each entry's rank in that empty value. No new lookup was needed: theRANKrecord function already computed exactly this, and it wanted a record only in order to evaluate the index key against it. Keying it off the index key instead lets a scanned entry be ranked without loading its record, and the record path reduces to producing that key first. The javadoc is explicit that the option is not free — it costs one ranked-set skip-list traversal per entry returned, so the cost grows with entries returned rather than with the range asked for.