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Merged
mpollmeier merged 1 commit into from
Sep 19, 2025
Merged

DiffGraph: allow simultaneous edge and node removal #347

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36 changes: 20 additions & 16 deletions core/src/main/scala/flatgraph/DiffGraphApplier.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -196,24 +196,28 @@ private[flatgraph] class DiffGraphApplier(
new EdgeRepr(inR.src, inR.dst, inR.edgeKind, inR.subSeq, setEdgeProperty.property),
graph.schema.neighborOffsetArrayIndex(inR.src.nodeKind, Incoming, inR.edgeKind)
)
case edgeDeletion: RemoveEdge
if !AccessHelpers.isDeleted(edgeDeletion.edge.src) && !AccessHelpers.isDeleted(edgeDeletion.edge.dst) =>
ndiff += 1
case edgeDeletion: RemoveEdge =>
if (AccessHelpers.isDeleted(edgeDeletion.edge.src) || AccessHelpers.isDeleted(edgeDeletion.edge.dst)) {
// the adjacent nodes have already been deleted - nothing more for us to do here
// and, importantly, we do not want to fail if that's the case, but simply relax and enjoy
} else {

/** This is the delEdge case. It is massively annoying.
*
* In order to support edge properties, we need to grab the right edge from e.src->e.dst. If we assume that our graph was built
* normally, i.e. edges were sequentially/batched added without the unsafe unidirectional edges, then our graph has the following
* invariant: The kth edge connecting A->B corresponds to the kth edge connecting B<-A This sucks big time, because edge removal
* is potentially O(N**2). The degenerate behavior occurs when we have ~k edges of the same type starting in src = X or ending in
* the same dst = X. Each deletion then costs us ~k, and if we delete all ~k edges we pay ~ k*k.
*
* But k~N is possible where N is the graph size!
*/
val (outR, inR) = normalizeRepresentation(edgeDeletion.edge)
insert(delEdges, outR, graph.schema.neighborOffsetArrayIndex(outR.src.nodeKind, Outgoing, outR.edgeKind))
insert(delEdges, inR, graph.schema.neighborOffsetArrayIndex(inR.src.nodeKind, Incoming, inR.edgeKind))
ndiff += 1

/** This is the delEdge case. It is massively annoying.
*
* In order to support edge properties, we need to grab the right edge from e.src->e.dst. If we assume that our graph was built
* normally, i.e. edges were sequentially/batched added without the unsafe unidirectional edges, then our graph has the
* following invariant: The kth edge connecting A->B corresponds to the kth edge connecting B<-A This sucks big time, because
* edge removal is potentially O(N**2). The degenerate behavior occurs when we have ~k edges of the same type starting in src =
* X or ending in the same dst = X. Each deletion then costs us ~k, and if we delete all ~k edges we pay ~ k*k.
*
* But k~N is possible where N is the graph size!
*/
val (outR, inR) = normalizeRepresentation(edgeDeletion.edge)
insert(delEdges, outR, graph.schema.neighborOffsetArrayIndex(outR.src.nodeKind, Outgoing, outR.edgeKind))
insert(delEdges, inR, graph.schema.neighborOffsetArrayIndex(inR.src.nodeKind, Incoming, inR.edgeKind))
}
case setNodeProperty: SetNodeProperty if !AccessHelpers.isDeleted(setNodeProperty.node) =>
ndiff += 1
val iter = setNodeProperty.property match {
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66 changes: 66 additions & 0 deletions core/src/test/scala/flatgraph/GraphTests.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -524,6 +524,72 @@ class GraphTests extends AnyWordSpec with Matchers {
testSerialization(g)
}

"permit deleting an edge together with it's node" in {
// if a node get's deleted we automatically delete the adjacent edges
// but if a user explicitly removes the edge (additionally) we do not want to fail hard for that...

var g = mkGraph()
debugDump(g) shouldBe
"""#Node numbers (kindId, nnodes) (0: 4), total 4
|Node kind 0. (eid, nEdgesOut, nEdgesIn): (0, 7 [dense], 7 [dense]),
| V0_0 [0] -> V0_2, V0_1, V0_3, V0_2, V0_1
| V0_1 [0] <- V0_0, V0_3, V0_0
| V0_2 [0] <- V0_0, V0_0, V0_3
| V0_3 [0] -> V0_1, V0_2
| V0_3 [0] <- V0_0
|""".stripMargin

val nodeToDelete = g.node(0, 0)
val edgeToDelete = Accessors.getEdgesOut(nodeToDelete, 0)(0)
DiffGraphApplier.applyDiff(
g,
new DiffGraphBuilder(schema)
.removeNode(nodeToDelete)
.removeEdge(edgeToDelete)
)

debugDump(g) shouldBe
"""#Node numbers (kindId, nnodes) (0: 4), total 4
|Node kind 0. (eid, nEdgesOut, nEdgesIn): (0, 2 [dense], 2 [dense]),
| V0_1 [0] <- V0_3
| V0_2 [0] <- V0_3
| V0_3 [0] -> V0_1, V0_2
|""".stripMargin

g = mkGraph()
DiffGraphApplier.applyDiff(
g,
new DiffGraphBuilder(schema)
.removeNode(g.node(0, 1))
)
debugDump(g) shouldBe
"""#Node numbers (kindId, nnodes) (0: 4), total 4
|Node kind 0. (eid, nEdgesOut, nEdgesIn): (0, 4 [dense], 4 [dense]),
| V0_0 [0] -> V0_2, V0_3, V0_2
| V0_2 [0] <- V0_0, V0_0, V0_3
| V0_3 [0] -> V0_2
| V0_3 [0] <- V0_0
|""".stripMargin

testSerialization(g)

g = mkGraph()
DiffGraphApplier.applyDiff(
g,
new DiffGraphBuilder(schema)
.removeNode(g.node(0, 2))
.removeNode(g.node(0, 3))
)
debugDump(g) shouldBe
"""#Node numbers (kindId, nnodes) (0: 4), total 4
|Node kind 0. (eid, nEdgesOut, nEdgesIn): (0, 2 [dense], 2 [dense]),
| V0_0 [0] -> V0_1, V0_1
| V0_1 [0] <- V0_0, V0_0
|""".stripMargin

testSerialization(g)
}

"dont mess up after node deletion" in {
val schema = TestSchema.make(1, 0, 1, nodePropertyPrototypes = Array(Array[String]("")), edgePropertyPrototypes = null)
val g = new Graph(schema)
Expand Down