feat: connector line ux

frontend/src/hooks/trace/useGetTraceFlamegraph.tsx

@@ -16,7 +16,7 @@ const useGetTraceFlamegraph = (
 		queryKey: [
 			REACT_QUERY_KEY.GET_TRACE_V2_FLAMEGRAPH,
 			props.traceId,
-			props.selectedSpanId,
+			// props.selectedSpanId,
 		],
 		enabled: !!props.traceId,
 		keepPreviousData: true,

frontend/src/pages/TraceDetailsV3/TraceFlamegraph/FlamegraphCanvas.tsx

@@ -11,6 +11,7 @@ import { useFlamegraphDraw } from './hooks/useFlamegraphDraw';
 import { useFlamegraphHover } from './hooks/useFlamegraphHover';
 import { useFlamegraphZoom } from './hooks/useFlamegraphZoom';
 import { useScrollToSpan } from './hooks/useScrollToSpan';
+import { useVisualLayoutWorker } from './hooks/useVisualLayoutWorker';
 import { FlamegraphCanvasProps, SpanRect } from './types';
 
 function FlamegraphCanvas(props: FlamegraphCanvasProps): JSX.Element {
@@ -58,7 +59,9 @@ function FlamegraphCanvas(props: FlamegraphCanvasProps): JSX.Element {
 		viewEndRef.current = traceMetadata.endTime;
 	}, [traceMetadata.startTime, traceMetadata.endTime]);
 
-	const totalHeight = spans.length * rowHeight;
+	const { layout, isComputing: _isComputing } = useVisualLayoutWorker(spans);
+
+	const totalHeight = layout.totalVisualRows * rowHeight;
 
 	const { isOverFlamegraphRef } = useFlamegraphZoom({
 		canvasRef,
@@ -112,7 +115,8 @@ function FlamegraphCanvas(props: FlamegraphCanvasProps): JSX.Element {
 	const { drawFlamegraph } = useFlamegraphDraw({
 		canvasRef,
 		containerRef,
-		spans,
+		spans: layout.visualRows,
+		connectors: layout.connectors,
 		viewStartTs,
 		viewEndTs,
 		scrollTop,
@@ -125,7 +129,7 @@ function FlamegraphCanvas(props: FlamegraphCanvasProps): JSX.Element {
 
 	useScrollToSpan({
 		firstSpanAtFetchLevel,
-		spans,
+		spans: layout.visualRows,
 		traceMetadata,
 		containerRef,
 		viewStartRef,

frontend/src/pages/TraceDetailsV3/TraceFlamegraph/TraceFlamegraph.tsx

@@ -43,7 +43,7 @@ function TraceFlamegraph(): JSX.Element {
 
 	const { data, isFetching, error } = useGetTraceFlamegraph({
 		traceId,
-		selectedSpanId: firstSpanAtFetchLevel,
+		// selectedSpanId: firstSpanAtFetchLevel,
 	});
 
 	const flamegraphState = useMemo(() => {

frontend/src/pages/TraceDetailsV3/TraceFlamegraph/__tests__/computeVisualLayout.test.ts

@@ -0,0 +1,475 @@
+import { FlamegraphSpan } from 'types/api/trace/getTraceFlamegraph';
+
+import { computeVisualLayout } from '../computeVisualLayout';
+
+function makeSpan(
+	overrides: Partial<FlamegraphSpan> & {
+		spanId: string;
+		timestamp: number;
+		durationNano: number;
+	},
+): FlamegraphSpan {
+	return {
+		parentSpanId: '',
+		traceId: 'trace-1',
+		hasError: false,
+		serviceName: 'svc',
+		name: 'op',
+		level: 0,
+		event: [],
+		...overrides,
+	};
+}
+
+describe('computeVisualLayout', () => {
+	it('should handle empty input', () => {
+		const layout = computeVisualLayout([]);
+		expect(layout.totalVisualRows).toBe(0);
+		expect(layout.visualRows).toEqual([]);
+	});
+
+	it('should handle single root, no children — 1 visual row', () => {
+		const root = makeSpan({
+			spanId: 'root',
+			timestamp: 0,
+			durationNano: 100e6,
+		});
+		const layout = computeVisualLayout([[root]]);
+		expect(layout.totalVisualRows).toBe(1);
+		expect(layout.visualRows[0]).toEqual([root]);
+		expect(layout.spanToVisualRow['root']).toBe(0);
+	});
+
+	it('should keep non-overlapping siblings on the same row (compact)', () => {
+		const root = makeSpan({
+			spanId: 'root',
+			timestamp: 0,
+			durationNano: 500e6,
+		});
+		const a = makeSpan({
+			spanId: 'a',
+			parentSpanId: 'root',
+			timestamp: 0,
+			durationNano: 100e6,
+		});
+		const b = makeSpan({
+			spanId: 'b',
+			parentSpanId: 'root',
+			timestamp: 200,
+			durationNano: 100e6,
+		});
+		const c = makeSpan({
+			spanId: 'c',
+			parentSpanId: 'root',
+			timestamp: 400,
+			durationNano: 100e6,
+		});
+
+		const layout = computeVisualLayout([[root], [a, b, c]]);
+
+		// root on row 0, all children on row 1
+		expect(layout.totalVisualRows).toBe(2);
+		expect(layout.spanToVisualRow['root']).toBe(0);
+		expect(layout.spanToVisualRow['a']).toBe(1);
+		expect(layout.spanToVisualRow['b']).toBe(1);
+		expect(layout.spanToVisualRow['c']).toBe(1);
+	});
+
+	it('should pack non-overlapping siblings into shared lanes (greedy packing)', () => {
+		const root = makeSpan({
+			spanId: 'root',
+			timestamp: 0,
+			durationNano: 300e6,
+		});
+		// A and B overlap; C does not overlap with either
+		const a = makeSpan({
+			spanId: 'a',
+			parentSpanId: 'root',
+			timestamp: 0,
+			durationNano: 100e6, // ends at 100ms
+		});
+		const b = makeSpan({
+			spanId: 'b',
+			parentSpanId: 'root',
+			timestamp: 50,
+			durationNano: 100e6, // starts at 50ms < 100ms end of A → overlap → lane 1
+		});
+		const c = makeSpan({
+			spanId: 'c',
+			parentSpanId: 'root',
+			timestamp: 200,
+			durationNano: 100e6, // 200 >= 100, fits lane 0 with A
+		});
+
+		const layout = computeVisualLayout([[root], [a, b, c]]);
+
+		// root on row 0, C placed first (latest) → row 1, B doesn't overlap C → row 1, A overlaps B → row 2
+		expect(layout.totalVisualRows).toBe(3);
+		expect(layout.spanToVisualRow['root']).toBe(0);
+		expect(layout.spanToVisualRow['c']).toBe(1);
+		expect(layout.spanToVisualRow['b']).toBe(1);
+		expect(layout.spanToVisualRow['a']).toBe(2);
+	});
+
+	it('should handle full overlap — all siblings get own row', () => {
+		const root = makeSpan({
+			spanId: 'root',
+			timestamp: 0,
+			durationNano: 200e6,
+		});
+		const a = makeSpan({
+			spanId: 'a',
+			parentSpanId: 'root',
+			timestamp: 0,
+			durationNano: 200e6,
+		});
+		const b = makeSpan({
+			spanId: 'b',
+			parentSpanId: 'root',
+			timestamp: 0,
+			durationNano: 200e6,
+		});
+
+		const layout = computeVisualLayout([[root], [a, b]]);
+
+		expect(layout.totalVisualRows).toBe(3);
+		expect(layout.spanToVisualRow['a']).toBe(1);
+		expect(layout.spanToVisualRow['b']).toBe(2);
+	});
+
+	it('should stack children correctly below overlapping parents', () => {
+		const root = makeSpan({
+			spanId: 'root',
+			timestamp: 0,
+			durationNano: 300e6,
+		});
+		const a = makeSpan({
+			spanId: 'a',
+			parentSpanId: 'root',
+			timestamp: 0,
+			durationNano: 200e6,
+		});
+		const b = makeSpan({
+			spanId: 'b',
+			parentSpanId: 'root',
+			timestamp: 50,
+			durationNano: 200e6,
+		});
+		// Child of A
+		const childA = makeSpan({
+			spanId: 'childA',
+			parentSpanId: 'a',
+			timestamp: 10,
+			durationNano: 50e6,
+		});
+		// Child of B
+		const childB = makeSpan({
+			spanId: 'childB',
+			parentSpanId: 'b',
+			timestamp: 60,
+			durationNano: 50e6,
+		});
+
+		const layout = computeVisualLayout([[root], [a, b], [childA, childB]]);
+
+		// DFS processes b's subtree first (latest):
+		// root → row 0
+		// b → row 1 (parentRow 0 + 1)
+		// childB → row 2 (parentRow 1 + 1)
+		// a → try row 1 (parentRow 0 + 1), overlaps b → try row 2, overlaps childB → row 3
+		// childA → row 4 (parentRow 3 + 1)
+		expect(layout.spanToVisualRow['root']).toBe(0);
+		expect(layout.spanToVisualRow['b']).toBe(1);
+		expect(layout.spanToVisualRow['childB']).toBe(2);
+		expect(layout.spanToVisualRow['a']).toBe(3);
+		expect(layout.spanToVisualRow['childA']).toBe(4);
+		expect(layout.totalVisualRows).toBe(5);
+	});
+
+	it('should handle multiple roots as a sibling group', () => {
+		// Two overlapping roots
+		const r1 = makeSpan({
+			spanId: 'r1',
+			timestamp: 0,
+			durationNano: 100e6,
+		});
+		const r2 = makeSpan({
+			spanId: 'r2',
+			timestamp: 50,
+			durationNano: 100e6,
+		});
+
+		const layout = computeVisualLayout([[r1, r2]]);
+
+		expect(layout.spanToVisualRow['r1']).toBe(0);
+		expect(layout.spanToVisualRow['r2']).toBe(1);
+		expect(layout.totalVisualRows).toBe(2);
+	});
+
+	it('should produce compact layout for deep nesting without overlap', () => {
+		const root = makeSpan({
+			spanId: 'root',
+			timestamp: 0,
+			durationNano: 1000e6,
+		});
+		const child = makeSpan({
+			spanId: 'child',
+			parentSpanId: 'root',
+			timestamp: 10,
+			durationNano: 500e6,
+		});
+		const grandchild = makeSpan({
+			spanId: 'grandchild',
+			parentSpanId: 'child',
+			timestamp: 20,
+			durationNano: 200e6,
+		});
+
+		const layout = computeVisualLayout([[root], [child], [grandchild]]);
+
+		// No overlap at any level → visual rows == tree depth
+		expect(layout.totalVisualRows).toBe(3);
+		expect(layout.spanToVisualRow['root']).toBe(0);
+		expect(layout.spanToVisualRow['child']).toBe(1);
+		expect(layout.spanToVisualRow['grandchild']).toBe(2);
+	});
+
+	it('should pack many sequential siblings into 1 row (no diagonal staircase)', () => {
+		const root = makeSpan({
+			spanId: 'root',
+			timestamp: 0,
+			durationNano: 500e6,
+		});
+		// 6 sequential children — like checkoutservice/PlaceOrder scenario
+		const spans = [
+			makeSpan({
+				spanId: 's1',
+				parentSpanId: 'root',
+				timestamp: 3,
+				durationNano: 30e6,
+			}),
+			makeSpan({
+				spanId: 's2',
+				parentSpanId: 'root',
+				timestamp: 35,
+				durationNano: 4e6,
+			}),
+			makeSpan({
+				spanId: 's3',
+				parentSpanId: 'root',
+				timestamp: 39,
+				durationNano: 1e6,
+			}),
+			makeSpan({
+				spanId: 's4',
+				parentSpanId: 'root',
+				timestamp: 40,
+				durationNano: 4e6,
+			}),
+			makeSpan({
+				spanId: 's5',
+				parentSpanId: 'root',
+				timestamp: 44,
+				durationNano: 5e6,
+			}),
+			makeSpan({
+				spanId: 's6',
+				parentSpanId: 'root',
+				timestamp: 49,
+				durationNano: 1e6,
+			}),
+		];
+
+		const layout = computeVisualLayout([[root], spans]);
+
+		// All 6 sequential siblings should share 1 row
+		expect(layout.totalVisualRows).toBe(2);
+		expect(layout.spanToVisualRow['root']).toBe(0);
+		for (const span of spans) {
+			expect(layout.spanToVisualRow[span.spanId]).toBe(1);
+		}
+	});
+
+	it('should keep children below parents even with misparented spans', () => {
+		// Simulates the dd_sig2 bug: /route spans have parentSpanId pointing
+		// to the wrong ancestor, but they are at level 2 in the spans[][] input.
+		// Level-based packing must place them below level 1 regardless.
+		const httpGet = makeSpan({
+			spanId: 'http-get',
+			timestamp: 0,
+			durationNano: 500e6,
+		});
+		const route = makeSpan({
+			spanId: 'route',
+			parentSpanId: 'some-wrong-ancestor', // misparented!
+			timestamp: 10,
+			durationNano: 200e6,
+		});
+
+		const layout = computeVisualLayout([[httpGet], [route]]);
+
+		// httpGet at level 0 → row 0, route at level 1 → row 1
+		expect(layout.spanToVisualRow['http-get']).toBe(0);
+		expect(layout.spanToVisualRow['route']).toBe(1);
+		expect(layout.totalVisualRows).toBe(2);
+	});
+
+	it('should keep parent-child pairs adjacent when sibling subtrees overlap', () => {
+		// Multiple overlapping parents each with a child — the subtree-unit
+		// guarantee means every parent→child gap should be exactly 1.
+		const root = makeSpan({
+			spanId: 'root',
+			timestamp: 0,
+			durationNano: 500e6,
+		});
+		// Three overlapping HTTP GET children of root, each with its own /route child
+		const get1 = makeSpan({
+			spanId: 'get1',
+			parentSpanId: 'root',
+			timestamp: 0,
+			durationNano: 200e6,
+		});
+		const route1 = makeSpan({
+			spanId: 'route1',
+			parentSpanId: 'get1',
+			timestamp: 10,
+			durationNano: 180e6,
+		});
+		const get2 = makeSpan({
+			spanId: 'get2',
+			parentSpanId: 'root',
+			timestamp: 50,
+			durationNano: 200e6,
+		});
+		const route2 = makeSpan({
+			spanId: 'route2',
+			parentSpanId: 'get2',
+			timestamp: 60,
+			durationNano: 180e6,
+		});
+		const get3 = makeSpan({
+			spanId: 'get3',
+			parentSpanId: 'root',
+			timestamp: 100,
+			durationNano: 200e6,
+		});
+		const route3 = makeSpan({
+			spanId: 'route3',
+			parentSpanId: 'get3',
+			timestamp: 110,
+			durationNano: 180e6,
+		});
+
+		const layout = computeVisualLayout([
+			[root],
+			[get1, get2, get3],
+			[route1, route2, route3],
+		]);
+
+		// Each parent-child pair should have a gap of exactly 1
+		const get1Row = layout.spanToVisualRow['get1'];
+		const route1Row = layout.spanToVisualRow['route1'];
+		const get2Row = layout.spanToVisualRow['get2'];
+		const route2Row = layout.spanToVisualRow['route2'];
+		const get3Row = layout.spanToVisualRow['get3'];
+		const route3Row = layout.spanToVisualRow['route3'];
+
+		expect(route1Row - get1Row).toBe(1);
+		expect(route2Row - get2Row).toBe(1);
+		expect(route3Row - get3Row).toBe(1);
+	});
+
+	it('should handle mixed levels — overlap at level 2 but not level 1', () => {
+		const root = makeSpan({
+			spanId: 'root',
+			timestamp: 0,
+			durationNano: 1000e6,
+		});
+		// Non-overlapping children
+		const a = makeSpan({
+			spanId: 'a',
+			parentSpanId: 'root',
+			timestamp: 0,
+			durationNano: 400e6,
+		});
+		const b = makeSpan({
+			spanId: 'b',
+			parentSpanId: 'root',
+			timestamp: 500,
+			durationNano: 400e6,
+		});
+		// Overlapping grandchildren under A
+		const ga1 = makeSpan({
+			spanId: 'ga1',
+			parentSpanId: 'a',
+			timestamp: 0,
+			durationNano: 200e6,
+		});
+		const ga2 = makeSpan({
+			spanId: 'ga2',
+			parentSpanId: 'a',
+			timestamp: 100,
+			durationNano: 200e6,
+		});
+
+		const layout = computeVisualLayout([[root], [a, b], [ga1, ga2]]);
+
+		// root → row 0
+		// a, b → row 1 (no overlap, share row)
+		// ga1 → row 2, ga2 → row 3 (overlap, expanded)
+		// b has no children, so nothing after ga2
+		expect(layout.spanToVisualRow['root']).toBe(0);
+		expect(layout.spanToVisualRow['a']).toBe(1);
+		expect(layout.spanToVisualRow['b']).toBe(1);
+		expect(layout.spanToVisualRow['ga2']).toBe(2);
+		expect(layout.spanToVisualRow['ga1']).toBe(3);
+		expect(layout.totalVisualRows).toBe(4);
+	});
+
+	it('should not place a span where it covers an existing connector point (Check 2)', () => {
+		// Scenario: root has 3 leaf children. Sorted latest-first: C(200), B(100), A(80).
+		//
+		// C placed at row 1 [200, 400].
+		// B overlaps C → placed at row 2 [100, 300]. Connector from row 0→2 at x=100
+		//   passes through row 1, recording connector point at (row 1, x=100).
+		// A [80, 110] does NOT overlap C's span [200, 400] at row 1 (110 < 200),
+		//   so without connector reservation A would fit at row 1.
+		//   But A's span [80, 110) contains the connector point x=100 at row 1.
+		//   Check 2 prevents this placement, pushing A further down.
+		const root = makeSpan({
+			spanId: 'root',
+			timestamp: 0,
+			durationNano: 500e6,
+		});
+		const c = makeSpan({
+			spanId: 'c',
+			parentSpanId: 'root',
+			timestamp: 200,
+			durationNano: 200e6, // [200, 400]
+		});
+		const b = makeSpan({
+			spanId: 'b',
+			parentSpanId: 'root',
+			timestamp: 100,
+			durationNano: 200e6, // [100, 300]
+		});
+		const a = makeSpan({
+			spanId: 'a',
+			parentSpanId: 'root',
+			timestamp: 80,
+			durationNano: 30e6, // [80, 110]
+		});
+
+		const layout = computeVisualLayout([[root], [a, b, c]]);
+
+		expect(layout.spanToVisualRow['root']).toBe(0);
+		expect(layout.spanToVisualRow['c']).toBe(1); // latest, placed first
+		expect(layout.spanToVisualRow['b']).toBe(2); // overlaps C → row 2
+
+		// A would fit at row 1 by span overlap alone, but connector point at
+		// (row 1, x=100) falls within A's span [80, 110). Check 2 pushes A down.
+		const aRow = layout.spanToVisualRow['a']!;
+		expect(aRow).toBeGreaterThan(1); // must NOT be at row 1
+		expect(aRow).toBe(3); // next free row after B at row 2 (A overlaps B)
+	});
+});

frontend/src/pages/TraceDetailsV3/TraceFlamegraph/computeVisualLayout.ts

@@ -0,0 +1,370 @@
+/* eslint-disable sonarjs/cognitive-complexity */
+import { FlamegraphSpan } from 'types/api/trace/getTraceFlamegraph';
+
+export interface ConnectorLine {
+	parentRow: number;
+	childRow: number;
+	timestampMs: number;
+	serviceName: string;
+}
+
+export interface VisualLayout {
+	visualRows: FlamegraphSpan[][];
+	spanToVisualRow: Record<string, number>;
+	connectors: ConnectorLine[];
+	totalVisualRows: number;
+}
+
+/**
+ * Computes an overlap-safe visual layout for flamegraph spans using DFS ordering.
+ *
+ * Builds a parent→children tree from parentSpanId, then traverses in DFS pre-order.
+ * Each span is placed at parentRow+1 if free, otherwise scans upward row-by-row
+ * until finding a non-overlapping row. This keeps children visually close to their
+ * parents and avoids the BFS problem where distant siblings push children far down.
+ */
+export function computeVisualLayout(spans: FlamegraphSpan[][]): VisualLayout {
+	const spanToVisualRow = new Map<string, number>();
+	const visualRowsMap = new Map<number, FlamegraphSpan[]>();
+	let maxRow = -1;
+
+	// Per-row interval list for overlap detection
+	// Each entry: [startTime, endTime]
+	const rowIntervals = new Map<number, Array<[number, number]>>();
+
+	// function hasOverlap(row: number, startTime: number, endTime: number): boolean {
+	// 	const intervals = rowIntervals.get(row);
+	// 	if (!intervals) {
+	// 		return false;
+	// 	}
+	// 	for (const [s, e] of intervals) {
+	// 		if (startTime < e && endTime > s) {
+	// 			return true;
+	// 		}
+	// 	}
+	// 	return false;
+	// }
+
+	function addToRow(row: number, span: FlamegraphSpan): void {
+		spanToVisualRow.set(span.spanId, row);
+		let arr = visualRowsMap.get(row);
+		if (!arr) {
+			arr = [];
+			visualRowsMap.set(row, arr);
+		}
+		arr.push(span);
+
+		const startTime = span.timestamp;
+		const endTime = span.timestamp + span.durationNano / 1e6;
+		let intervals = rowIntervals.get(row);
+		if (!intervals) {
+			intervals = [];
+			rowIntervals.set(row, intervals);
+		}
+		intervals.push([startTime, endTime]);
+
+		if (row > maxRow) {
+			maxRow = row;
+		}
+	}
+
+	// Flatten all spans and build lookup + children map
+	const spanMap = new Map<string, FlamegraphSpan>();
+	const childrenMap = new Map<string, FlamegraphSpan[]>();
+	const allSpans: FlamegraphSpan[] = [];
+
+	for (const level of spans) {
+		for (const span of level) {
+			allSpans.push(span);
+			spanMap.set(span.spanId, span);
+		}
+	}
+
+	// Extract parentSpanId — the field may be missing at runtime when the API
+	// returns `references` instead.  Fall back to the first CHILD_OF reference.
+	function getParentId(span: FlamegraphSpan): string {
+		if (span.parentSpanId) {
+			return span.parentSpanId;
+		}
+		// eslint-disable-next-line @typescript-eslint/no-explicit-any
+		const refs = (span as any).references as
+			| Array<{ spanId?: string; refType?: string }>
+			| undefined;
+		if (refs) {
+			for (const ref of refs) {
+				if (ref.refType === 'CHILD_OF' && ref.spanId) {
+					return ref.spanId;
+				}
+			}
+		}
+		return '';
+	}
+
+	// Build children map and identify roots
+	const roots: FlamegraphSpan[] = [];
+
+	for (const span of allSpans) {
+		const parentId = getParentId(span);
+		if (!parentId || !spanMap.has(parentId)) {
+			roots.push(span);
+		} else {
+			let children = childrenMap.get(parentId);
+			if (!children) {
+				children = [];
+				childrenMap.set(parentId, children);
+			}
+			children.push(span);
+		}
+	}
+
+	// Sort children by timestamp for deterministic ordering
+	for (const [, children] of childrenMap) {
+		children.sort((a, b) => b.timestamp - a.timestamp);
+	}
+
+	// --- Subtree-unit placement ---
+	// Compute each subtree's layout in isolation, then place as a unit
+	// to guarantee parent-child adjacency within subtrees.
+
+	interface ShapeEntry {
+		span: FlamegraphSpan;
+		relativeRow: number;
+	}
+
+	function hasOverlapIn(
+		intervals: Map<number, Array<[number, number]>>,
+		row: number,
+		startTime: number,
+		endTime: number,
+	): boolean {
+		const rowIntervals = intervals.get(row);
+		if (!rowIntervals) {
+			return false;
+		}
+		for (const [s, e] of rowIntervals) {
+			if (startTime < e && endTime > s) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	function addIntervalTo(
+		intervals: Map<number, Array<[number, number]>>,
+		row: number,
+		startTime: number,
+		endTime: number,
+	): void {
+		let arr = intervals.get(row);
+		if (!arr) {
+			arr = [];
+			intervals.set(row, arr);
+		}
+		arr.push([startTime, endTime]);
+	}
+
+	function hasConnectorConflict(
+		intervals: Map<number, Array<[number, number]>>,
+		row: number,
+		point: number,
+	): boolean {
+		const rowIntervals = intervals.get(row);
+		if (!rowIntervals) {
+			return false;
+		}
+		for (const [s, e] of rowIntervals) {
+			if (point >= s && point < e) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	function hasPointInSpan(
+		connectorPoints: Map<number, number[]>,
+		row: number,
+		startTime: number,
+		endTime: number,
+	): boolean {
+		const points = connectorPoints.get(row);
+		if (!points) {
+			return false;
+		}
+		for (const p of points) {
+			if (p >= startTime && p < endTime) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	function addConnectorPoint(
+		connectorPoints: Map<number, number[]>,
+		row: number,
+		point: number,
+	): void {
+		let arr = connectorPoints.get(row);
+		if (!arr) {
+			arr = [];
+			connectorPoints.set(row, arr);
+		}
+		arr.push(point);
+	}
+
+	function computeSubtreeShape(rootSpan: FlamegraphSpan): ShapeEntry[] {
+		const localIntervals = new Map<number, Array<[number, number]>>();
+		const localConnectorPoints = new Map<number, number[]>();
+		const shape: ShapeEntry[] = [];
+
+		// Place root span at relative row 0
+		const rootStart = rootSpan.timestamp;
+		const rootEnd = rootSpan.timestamp + rootSpan.durationNano / 1e6;
+		shape.push({ span: rootSpan, relativeRow: 0 });
+		addIntervalTo(localIntervals, 0, rootStart, rootEnd);
+
+		const children = childrenMap.get(rootSpan.spanId);
+		if (children) {
+			for (const child of children) {
+				const childShape = computeSubtreeShape(child);
+				const connectorX = child.timestamp;
+				const offset = findPlacement(
+					childShape,
+					1,
+					localIntervals,
+					localConnectorPoints,
+					connectorX,
+				);
+
+				// Record connector points for intermediate rows (1 to offset-1)
+				for (let r = 1; r < offset; r++) {
+					addConnectorPoint(localConnectorPoints, r, connectorX);
+				}
+
+				// Place child shape into local state at offset
+				for (const entry of childShape) {
+					const actualRow = entry.relativeRow + offset;
+					shape.push({ span: entry.span, relativeRow: actualRow });
+					const s = entry.span.timestamp;
+					const e = entry.span.timestamp + entry.span.durationNano / 1e6;
+					addIntervalTo(localIntervals, actualRow, s, e);
+				}
+			}
+		}
+
+		return shape;
+	}
+
+	function findPlacement(
+		shape: ShapeEntry[],
+		minOffset: number,
+		intervals: Map<number, Array<[number, number]>>,
+		connectorPoints?: Map<number, number[]>,
+		connectorX?: number,
+	): number {
+		// Track the first offset that passes Checks 1 & 2 as a fallback.
+		// Check 3 (connector vs span) is monotonically failing: once it fails
+		// at offset K, all offsets > K also fail (more intermediate rows).
+		// If we can't satisfy Check 3, fall back to the best offset without it.
+		let fallbackOffset = -1;
+
+		for (let offset = minOffset; ; offset++) {
+			let passesSpanChecks = true;
+
+			// Check 1: span vs span (existing)
+			for (const entry of shape) {
+				const targetRow = entry.relativeRow + offset;
+				const s = entry.span.timestamp;
+				const e = entry.span.timestamp + entry.span.durationNano / 1e6;
+				if (hasOverlapIn(intervals, targetRow, s, e)) {
+					passesSpanChecks = false;
+					break;
+				}
+			}
+
+			// Check 2: span vs existing connector points
+			if (passesSpanChecks && connectorPoints) {
+				for (const entry of shape) {
+					const targetRow = entry.relativeRow + offset;
+					const s = entry.span.timestamp;
+					const e = entry.span.timestamp + entry.span.durationNano / 1e6;
+					if (hasPointInSpan(connectorPoints, targetRow, s, e)) {
+						passesSpanChecks = false;
+						break;
+					}
+				}
+			}
+
+			if (!passesSpanChecks) {
+				continue;
+			}
+
+			// This offset passes Checks 1 & 2 — record as fallback
+			if (fallbackOffset === -1) {
+				fallbackOffset = offset;
+			}
+
+			// Check 3: new connector vs existing spans
+			if (connectorX !== undefined) {
+				let connectorClear = true;
+				for (let r = 1; r < offset; r++) {
+					if (hasConnectorConflict(intervals, r, connectorX)) {
+						connectorClear = false;
+						break;
+					}
+				}
+				if (!connectorClear) {
+					// Check 3 will fail for all larger offsets too.
+					// Fall back to the first offset that passed Checks 1 & 2.
+					return fallbackOffset;
+				}
+			}
+
+			return offset;
+		}
+	}
+
+	// Process roots sorted by timestamp
+	roots.sort((a, b) => a.timestamp - b.timestamp);
+	for (const root of roots) {
+		const shape = computeSubtreeShape(root);
+		const offset = findPlacement(shape, 0, rowIntervals);
+		for (const entry of shape) {
+			addToRow(entry.relativeRow + offset, entry.span);
+		}
+	}
+
+	// Build the visualRows array
+	const totalVisualRows = maxRow + 1;
+	const visualRows: FlamegraphSpan[][] = [];
+	for (let i = 0; i < totalVisualRows; i++) {
+		visualRows.push(visualRowsMap.get(i) || []);
+	}
+
+	// Build connector lines for parent-child pairs with row gap > 1
+	const connectors: ConnectorLine[] = [];
+	for (const [parentId, children] of childrenMap) {
+		const parentRow = spanToVisualRow.get(parentId);
+		if (parentRow === undefined) {
+			continue;
+		}
+		for (const child of children) {
+			const childRow = spanToVisualRow.get(child.spanId);
+			if (childRow === undefined || childRow - parentRow <= 1) {
+				continue;
+			}
+			connectors.push({
+				parentRow,
+				childRow,
+				timestampMs: child.timestamp,
+				serviceName: child.serviceName,
+			});
+		}
+	}
+
+	return {
+		visualRows,
+		spanToVisualRow: Object.fromEntries(spanToVisualRow),
+		connectors,
+		totalVisualRows,
+	};
+}

frontend/src/pages/TraceDetailsV3/TraceFlamegraph/hooks/useFlamegraphDraw.ts

@@ -1,6 +1,9 @@
 import React, { RefObject, useCallback, useRef } from 'react';
+import { themeColors } from 'constants/theme';
+import { generateColor } from 'lib/uPlotLib/utils/generateColor';
 import { FlamegraphSpan } from 'types/api/trace/getTraceFlamegraph';
 
+import { ConnectorLine } from '../computeVisualLayout';
 import { SpanRect } from '../types';
 import {
 	clamp,
@@ -14,6 +17,7 @@ interface UseFlamegraphDrawArgs {
 	canvasRef: RefObject<HTMLCanvasElement>;
 	containerRef: RefObject<HTMLDivElement>;
 	spans: FlamegraphSpan[][];
+	connectors: ConnectorLine[];
 	viewStartTs: number;
 	viewEndTs: number;
 	scrollTop: number;
@@ -114,6 +118,68 @@ function drawLevel(args: DrawLevelArgs): void {
 	}
 }
 
+interface DrawConnectorLinesArgs {
+	ctx: CanvasRenderingContext2D;
+	connectors: ConnectorLine[];
+	scrollTop: number;
+	viewStartTs: number;
+	timeSpan: number;
+	cssWidth: number;
+	viewportHeight: number;
+	metrics: FlamegraphRowMetrics;
+}
+
+function drawConnectorLines(args: DrawConnectorLinesArgs): void {
+	const {
+		ctx,
+		connectors,
+		scrollTop,
+		viewStartTs,
+		timeSpan,
+		cssWidth,
+		viewportHeight,
+		metrics,
+	} = args;
+
+	ctx.save();
+	ctx.lineWidth = 1;
+	ctx.globalAlpha = 0.6;
+
+	for (const conn of connectors) {
+		const xFrac = (conn.timestampMs - viewStartTs) / timeSpan;
+		if (xFrac < -0.01 || xFrac > 1.01) {
+			continue;
+		}
+
+		const parentY =
+			conn.parentRow * metrics.ROW_HEIGHT -
+			scrollTop +
+			metrics.SPAN_BAR_Y_OFFSET +
+			metrics.SPAN_BAR_HEIGHT;
+		const childY =
+			conn.childRow * metrics.ROW_HEIGHT - scrollTop + metrics.SPAN_BAR_Y_OFFSET;
+
+		// Skip if entirely outside viewport
+		if (parentY > viewportHeight || childY < 0) {
+			continue;
+		}
+
+		const color = generateColor(
+			conn.serviceName,
+			themeColors.traceDetailColorsV3,
+		);
+		ctx.strokeStyle = color;
+
+		const x = clamp(xFrac * cssWidth, 0, cssWidth);
+		ctx.beginPath();
+		ctx.moveTo(x, parentY);
+		ctx.lineTo(x, childY);
+		ctx.stroke();
+	}
+
+	ctx.restore();
+}
+
 export function useFlamegraphDraw(
 	args: UseFlamegraphDrawArgs,
 ): UseFlamegraphDrawResult {
@@ -121,6 +187,7 @@ export function useFlamegraphDraw(
 		canvasRef,
 		containerRef,
 		spans,
+		connectors,
 		viewStartTs,
 		viewEndTs,
 		scrollTop,
@@ -173,6 +240,18 @@ export function useFlamegraphDraw(
 
 		ctx.clearRect(0, 0, cssWidth, viewportHeight);
 
+		// ---- Draw connector lines (behind span bars) ----
+		drawConnectorLines({
+			ctx,
+			connectors,
+			scrollTop,
+			viewStartTs,
+			timeSpan,
+			cssWidth,
+			viewportHeight,
+			metrics,
+		});
+
 		const spanRectsArray: SpanRect[] = [];
 
 		// ---- Draw only visible levels ----
@@ -204,6 +283,7 @@ export function useFlamegraphDraw(
 		containerRef,
 		spanRectsRef,
 		spans,
+		connectors,
 		viewStartTs,
 		viewEndTs,
 		scrollTop,

frontend/src/pages/TraceDetailsV3/TraceFlamegraph/hooks/useFlamegraphHover.ts

@@ -47,6 +47,7 @@ function findSpanAtPosition(
 }
 
 export interface TooltipContent {
+	serviceName: string;
 	spanName: string;
 	status: 'ok' | 'warning' | 'error';
 	startMs: number;
@@ -139,6 +140,7 @@ export function useFlamegraphHover(
 			if (span) {
 				setHoveredSpanId(span.spanId);
 				setTooltipContent({
+					serviceName: span.serviceName || '',
 					spanName: span.name || 'unknown',
 					status: span.hasError ? 'error' : 'ok',
 					startMs: span.timestamp - traceMetadata.startTime,

frontend/src/pages/TraceDetailsV3/TraceFlamegraph/hooks/useVisualLayoutWorker.ts

@@ -0,0 +1,98 @@
+import { useEffect, useRef, useState } from 'react';
+import { FlamegraphSpan } from 'types/api/trace/getTraceFlamegraph';
+
+import { computeVisualLayout, VisualLayout } from '../computeVisualLayout';
+import { LayoutWorkerResponse } from '../visualLayoutWorkerTypes';
+
+const EMPTY_LAYOUT: VisualLayout = {
+	visualRows: [],
+	spanToVisualRow: {},
+	connectors: [],
+	totalVisualRows: 0,
+};
+
+function computeLayoutOrEmpty(spans: FlamegraphSpan[][]): VisualLayout {
+	return spans.length ? computeVisualLayout(spans) : EMPTY_LAYOUT;
+}
+
+function createLayoutWorker(): Worker {
+	return new Worker(new URL('../visualLayout.worker.ts', import.meta.url), {
+		type: 'module',
+	});
+}
+
+export function useVisualLayoutWorker(
+	spans: FlamegraphSpan[][],
+): { layout: VisualLayout; isComputing: boolean } {
+	const [layout, setLayout] = useState<VisualLayout>(EMPTY_LAYOUT);
+	const [isComputing, setIsComputing] = useState(false);
+	const workerRef = useRef<Worker | null>(null);
+	const requestIdRef = useRef(0);
+	const fallbackRef = useRef(typeof Worker === 'undefined');
+
+	// Effect: post message to worker when spans change
+	useEffect(() => {
+		if (fallbackRef.current) {
+			setLayout(computeLayoutOrEmpty(spans));
+			return;
+		}
+
+		if (!workerRef.current) {
+			try {
+				workerRef.current = createLayoutWorker();
+			} catch {
+				fallbackRef.current = true;
+				setLayout(computeLayoutOrEmpty(spans));
+				return;
+			}
+		}
+
+		if (!spans.length) {
+			setLayout(EMPTY_LAYOUT);
+			return;
+		}
+
+		const currentId = ++requestIdRef.current;
+		setIsComputing(true);
+
+		const worker = workerRef.current;
+
+		const onMessage = (e: MessageEvent<LayoutWorkerResponse>): void => {
+			if (e.data.requestId !== requestIdRef.current) {
+				return;
+			}
+			if (e.data.type === 'result') {
+				setLayout(e.data.layout);
+			} else {
+				setLayout(computeVisualLayout(spans));
+			}
+			setIsComputing(false);
+		};
+
+		const onError = (): void => {
+			if (requestIdRef.current === currentId) {
+				setLayout(computeVisualLayout(spans));
+				setIsComputing(false);
+			}
+		};
+
+		worker.addEventListener('message', onMessage);
+		worker.addEventListener('error', onError);
+		worker.postMessage({ type: 'compute', requestId: currentId, spans });
+
+		return (): void => {
+			worker.removeEventListener('message', onMessage);
+			worker.removeEventListener('error', onError);
+		};
+	}, [spans]);
+
+	// Cleanup worker on unmount
+	useEffect(
+		() => (): void => {
+			workerRef.current?.terminate();
+		},
+		[],
+	);
+
+	return { layout, isComputing };
+}

frontend/src/pages/TraceDetailsV3/TraceFlamegraph/visualLayout.worker.ts

@@ -0,0 +1,26 @@
+/// <reference lib="webworker" />
+import { computeVisualLayout } from './computeVisualLayout';
+import {
+	LayoutWorkerRequest,
+	LayoutWorkerResponse,
+} from './visualLayoutWorkerTypes';
+
+self.onmessage = (event: MessageEvent<LayoutWorkerRequest>): void => {
+	const { requestId, spans } = event.data;
+	try {
+		const layout = computeVisualLayout(spans);
+		const response: LayoutWorkerResponse = {
+			type: 'result',
+			requestId,
+			layout,
+		};
+		self.postMessage(response);
+	} catch (err) {
+		const response: LayoutWorkerResponse = {
+			type: 'error',
+			requestId,
+			message: String(err),
+		};
+		self.postMessage(response);
+	}
+};

frontend/src/pages/TraceDetailsV3/TraceFlamegraph/visualLayoutWorkerTypes.ts

@@ -0,0 +1,13 @@
+import { FlamegraphSpan } from 'types/api/trace/getTraceFlamegraph';
+
+import { VisualLayout } from './computeVisualLayout';
+
+export interface LayoutWorkerRequest {
+	type: 'compute';
+	requestId: number;
+	spans: FlamegraphSpan[][];
+}
+
+export type LayoutWorkerResponse =
+	| { type: 'result'; requestId: number; layout: VisualLayout }
+	| { type: 'error'; requestId: number; message: string };

frontend/src/types/api/trace/getTraceFlamegraph.ts

@@ -4,7 +4,7 @@ export interface TraceDetailFlamegraphURLProps {
 
 export interface GetTraceFlamegraphPayloadProps {
 	traceId: string;
-	selectedSpanId: string;
+	selectedSpanId?: string;
 }
 
 export interface Event {