levels: Compaction incorrectly drops delete markers #1422
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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").
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Reviewed 2 of 2 files at r1.
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| @@ -484,11 +484,8 @@ func (s *levelsController) compactBuildTables( | |||
| botTables := cd.bot | |||
|
|
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| // Check overlap of the top level with the levels which are not being | |||
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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").
jarifibrahim
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Aug 18, 2020
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)
NamanJain8
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Sep 8, 2020
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)
NamanJain8
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Sep 9, 2020
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>
jarifibrahim
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Oct 2, 2020
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").
mYmNeo
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Jan 16, 2023
) (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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This took me a ridiculous amount of time to track down.
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 (i.e. deleted keys are reappearing).
During compaction,
*levelsController.compactBuildTablesdecides 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
toptable, thinking that proving that thetoptable doesn't overlap is sufficient to prove that thebottomtable doesn't. Unfortunately, this is not the case. Not in general, and even less in the case ofDropPrefix()where we run a same-level compaction andtopis empty.The faulty condition was introduced way back when in e597fb7 ("Discard key versions during compaction").
This change is