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fix(query): evict highest-cost node when MaxFrontierSize exceeded in shortest path #9607

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fix(query): evict highest-cost node when MaxFrontierSize exceeded in shortest path #9607

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20 changes: 18 additions & 2 deletions query/shortest.go
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Original file line number Diff line number Diff line change
Expand Up @@ -88,6 +88,22 @@ func (h *priorityQueue) Pop() interface{} {
return val
}

// removeMax removes and returns the highest cost item from the priority queue.
// This is used to evict the least promising node when the frontier exceeds its
// size limit, preserving the lowest cost nodes needed for shortest paths.
func (h *priorityQueue) removeMax() {
if len(*h) == 0 {
return
}
maxIdx := 0
for i := 1; i < len(*h); i++ {
if (*h)[i].cost > (*h)[maxIdx].cost {
maxIdx = i
}
}
heap.Remove(h, maxIdx)
}

type mapItem struct {
attr string
cost float64
Expand Down Expand Up @@ -406,7 +422,7 @@ func runKShortestPaths(ctx context.Context, sg *SubGraph) ([]*SubGraph, error) {
path: route{route: curPath},
}
if int64(pq.Len()) > sg.Params.MaxFrontierSize {
pq.Pop()
pq.removeMax()
}
heap.Push(&pq, node)
}
Expand Down Expand Up @@ -562,7 +578,7 @@ func shortestPath(ctx context.Context, sg *SubGraph) ([]*SubGraph, error) {
hop: item.hop + 1,
}
if int64(pq.Len()) > sg.Params.MaxFrontierSize {
pq.Pop()
pq.removeMax()
}
heap.Push(&pq, node)
} else {
Expand Down