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Speed up LCA check #4754

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Speed up LCA check #4754

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42 changes: 16 additions & 26 deletions codebase2/codebase-sqlite/U/Codebase/Sqlite/Queries.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -2756,32 +2756,22 @@ before x y =
selectAncestorsOfY = ancestorSql y

lca :: CausalHashId -> CausalHashId -> Transaction (Maybe CausalHashId)
lca x y =
queryStreamCol (ancestorSql x) \nextX ->
queryStreamCol (ancestorSql y) \nextY -> do
let getNext = (,) <$> nextX <*> nextY
loop2 seenX seenY =
getNext >>= \case
(Just px, Just py) ->
let seenX' = Set.insert px seenX
seenY' = Set.insert py seenY
in if Set.member px seenY'
then pure (Just px)
else
if Set.member py seenX'
then pure (Just py)
else loop2 seenX' seenY'
(Nothing, Nothing) -> pure Nothing
(Just px, Nothing) -> loop1 nextX seenY px
(Nothing, Just py) -> loop1 nextY seenX py
loop1 getNext matches v =
if Set.member v matches
then pure (Just v)
else
getNext >>= \case
Just v -> loop1 getNext matches v
Nothing -> pure Nothing
loop2 (Set.singleton x) (Set.singleton y)
lca x y = do
queryMaybeCol
[sql|
WITH x_ancestors(id) AS (
$selectAncestorsOfX
), y_ancestors(id) AS (
$selectAncestorsOfY
) SELECT id FROM (
SELECT id FROM x_ancestors
INTERSECT
SELECT id FROM y_ancestors
) LIMIT 1
Comment on lines +2762 to +2770
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I haven't tested this, (maybe I need a table alias?)

Not sure there's any guarantee of correct row order coming out of an INTERSECT, so should probably find a way to do that or we might not get the LEAST common ancestor.

|]
where
selectAncestorsOfX = ancestorSql x
selectAncestorsOfY = ancestorSql y

ancestorSql :: CausalHashId -> Sql
ancestorSql h =
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