(release/v1.6) levels: Compaction incorrectly drops some delete markers (#1422)#1507
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NamanJain8 merged 3 commits intorelease/v1.6from Sep 9, 2020
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(release/v1.6) levels: Compaction incorrectly drops some delete markers (#1422)#1507NamanJain8 merged 3 commits intorelease/v1.6from
NamanJain8 merged 3 commits intorelease/v1.6from
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fd89894 ("Compaction: Expired keys and delete markers are never purged") revealed a bug in the compaction logic that leads to delete markers being incorrectly dropped during compaction. During compaction, `*levelsController.compactBuildTables` decides to drop a delete key if there is no overlap with levels lower than the bottom layer of the compaction definition. It does that by checking only the `top` table, thinking that proving that the `top` table doesn't overlap is sufficient to prove that the `bottom` table doesn't. Unfortunately, this is not the case. Not in general, and even less in the case of `DropPrefix()` where we run a same-level compaction and `top` is empty. The faulty condition was introduced way back when in e597fb7 ("Discard key versions during compaction"). (cherry picked from commit 5b90893)
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) (dgraph-io#1507) fd89894 ("Compaction: Expired keys and delete markers are never purged") revealed a bug in the compaction logic that leads to delete markers being incorrectly dropped during compaction. During compaction, `*levelsController.compactBuildTables` decides to drop a delete key if there is no overlap with levels lower than the bottom layer of the compaction definition. It does that by checking only the `top` table, thinking that proving that the `top` table doesn't overlap is sufficient to prove that the `bottom` table doesn't. Unfortunately, this is not the case. Not in general, and even less in the case of `DropPrefix()` where we run a same-level compaction and `top` is empty. The faulty condition was introduced way back when in e597fb7 ("Discard key versions during compaction"). (cherry picked from commit 5b90893) Co-authored-by: Damien Tournoud <damien@platform.sh>
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fd89894 ("Compaction: Expired keys and delete markers are never
purged") revealed a bug in the compaction logic that leads to delete
markers being incorrectly dropped during compaction.
During compaction,
*levelsController.compactBuildTablesdecides todrop a delete key if there is no overlap with levels lower than the
bottom layer of the compaction definition.
It does that by checking only the
toptable, thinking that provingthat the
toptable doesn't overlap is sufficient to prove thatthe
bottomtable doesn't. Unfortunately, this is not the case.Not in general, and even less in the case of
DropPrefix()wherewe run a same-level compaction and
topis empty.The faulty condition was introduced way back when in e597fb7
("Discard key versions during compaction").
(cherry picked from commit 5b90893)
This change is