db: only switch to combined iteration on RangeKeySet keys#1856
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jbowens merged 1 commit intocockroachdb:masterfrom Aug 5, 2022
Merged
db: only switch to combined iteration on RangeKeySet keys#1856jbowens merged 1 commit intocockroachdb:masterfrom
jbowens merged 1 commit intocockroachdb:masterfrom
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Race metamorphic tests revealed a problem. We need to hold D.mu to read table stats. I think this shouldn't be too hard to relax.
Reviewable status: 0 of 13 files reviewed, all discussions resolved
Previously, the lazy combined iterator always switched to combined iteration when it observed a file for which `m.HasRangeKeys` was true. This change tweaks the table stats to record the number of `RangeKeySets` within a file. Now, if table stats have been calculated for a file and the lazy combined iterator observes it has no `RangeKeySet`s, the lazy combined iterator will NOT trigger a switch. In Cockroach, this is expected to help when snapshot ingested RANGEKEYDELs. Cockroach lays both a RANGEDEL and RANGEKEYDEL across a range's snapshot sstable. Previously, iterating onto this sstable would unconditionally trigger a switch to combined iteration. Additionally, fix a bug where a combined iterator that was non-lazy due to batch or memtable range keys was incorrectly recorded as lazy. This would cause an unnecessary rebuild of the iterator stack on the first encounter of a range key. Close cockroachdb#1839.
itsbilal
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Reviewed 13 of 13 files at r1, 7 of 7 files at r2, all commit messages.
Reviewable status:complete! all files reviewed, all discussions resolved (waiting on @jbowens)
jbowens
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TFTR!
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Previously, the lazy combined iterator always switched to combined iteration
when it observed a file for which
m.HasRangeKeyswas true. This change tweaksthe table stats to record the number of
RangeKeySetswithin a file. Now, iftable stats have been calculated for a file and the lazy combined iterator
observes it has no
RangeKeySets, the lazy combined iterator will NOT triggera switch.
In Cockroach, this is expected to help with snapshot ingested RANGEKEYDELs.
Cockroach lays both a RANGEDEL and RANGEKEYDEL across a range's snapshot
sstable. Previously, iterating onto this sstable would unconditionally trigger
a switch to combined iteration.
Additionally, fix a bug where a combined iterator that was non-lazy due to
batch or memtable range keys was incorrectly recorded as lazy. This would cause
an unnecessary rebuild of the iterator stack on the first encounter of a range
key.
Close #1839.