perf(ui): fix O(n²) reactive subscriptions in timeline effects (HUGE SPEED IMPROVEMENT) (#274)
## Summary - Wraps store-proxied array iteration in `untrack()` in two `createEffect` blocks and one `createMemo` in `message-section.tsx` to prevent SolidJS from creating O(n) per-element reactive subscriptions on every run - Replaces `ids.includes()` with `Set.has()` for O(1) cleanup lookups in the part-count tracking effect ## Problem Two `createEffect` blocks in `message-section.tsx` iterate the `messageIds()` store proxy array inside a tracked reactive context. This causes SolidJS to create **O(n) per-element subscriptions** on every run. When any element changes, all n subscriptions fire, re-running the entire effect — resulting in **O(n²) total work**. Additionally, the cleanup loop in the part-count tracking effect uses `ids.includes(trackedId)` which is O(n) per tracked ID, compounding to O(n²). For long-running sessions with large message history (e.g. 7569 messages), this caused **~4.8 seconds of input latency** when sending a new prompt. ## Fix 1. **Timeline sync effect (~line 738):** Wrap entire body in `untrack()`, replace `ids.slice()` with `[...ids]` to snapshot without proxy tracking 2. **Part-count tracking effect (~line 891):** Wrap iteration in `untrack()`, replace `ids.includes()` with `new Set(ids).has()` for O(1) lookups 3. **`lastAssistantIndex` memo:** Read message records via `untrack()` to avoid O(n) subscriptions on part-level updates ## Result On a 7569-message session: prompt input latency reduced from **~4.8s to ~42ms** (114x improvement).
This commit is contained in:
Pascal André
@@ -129,6 +129,8 @@ export default function MessageSection(props: MessageSectionProps) {
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return map
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})
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const lastAssistantMessageId = createMemo(() => store().getLastAssistantMessageId(props.sessionId))
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const lastCompactionIndex = createMemo(() => {
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// Depend on a single session revision signal (not every message/part read)
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// to keep reactive overhead small.
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@@ -315,15 +317,9 @@ export default function MessageSection(props: MessageSectionProps) {
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}
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const lastAssistantIndex = createMemo(() => {
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const ids = messageIds()
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const resolvedStore = store()
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for (let index = ids.length - 1; index >= 0; index--) {
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const record = resolvedStore.getMessage(ids[index])
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if (record?.role === "assistant") {
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return index
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}
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}
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return -1
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const messageId = lastAssistantMessageId()
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if (!messageId) return -1
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return messageIndexById().get(messageId) ?? -1
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})
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const [timelineSegments, setTimelineSegments] = createSignal<TimelineSegment[]>([])
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@@ -734,88 +730,93 @@ export default function MessageSection(props: MessageSectionProps) {
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const loading = Boolean(props.loading)
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const ids = messageIds()
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if (loading) {
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handleClearTimelineSelection()
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previousTimelineIds = []
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setTimelineSegments([])
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seenTimelineMessageIds.clear()
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seenTimelineSegmentKeys.clear()
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timelinePartCountsByMessageId.clear()
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pendingTimelineMessagePartUpdates.clear()
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if (pendingTimelinePartUpdateFrame !== null) {
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cancelAnimationFrame(pendingTimelinePartUpdateFrame)
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pendingTimelinePartUpdateFrame = null
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}
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return
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}
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if (previousTimelineIds.length === 0 && ids.length > 0) {
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seedTimeline()
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previousTimelineIds = ids.slice()
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return
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}
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if (ids.length < previousTimelineIds.length) {
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seedTimeline()
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previousTimelineIds = ids.slice()
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return
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}
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if (ids.length === previousTimelineIds.length) {
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let changedIndex = -1
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let changeCount = 0
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for (let index = 0; index < ids.length; index++) {
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if (ids[index] !== previousTimelineIds[index]) {
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changedIndex = index
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changeCount += 1
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if (changeCount > 1) break
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// Wrap all iteration of the store-proxied `ids` array in untrack()
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// to prevent O(n) per-element reactive subscriptions. The effect
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// only needs to re-run when `messageIds` (memo) changes.
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untrack(() => {
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if (loading) {
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handleClearTimelineSelection()
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previousTimelineIds = []
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setTimelineSegments([])
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seenTimelineMessageIds.clear()
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seenTimelineSegmentKeys.clear()
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timelinePartCountsByMessageId.clear()
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pendingTimelineMessagePartUpdates.clear()
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if (pendingTimelinePartUpdateFrame !== null) {
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cancelAnimationFrame(pendingTimelinePartUpdateFrame)
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pendingTimelinePartUpdateFrame = null
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}
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return
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}
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if (changeCount === 1 && changedIndex >= 0) {
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const oldId = previousTimelineIds[changedIndex]
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const newId = ids[changedIndex]
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if (seenTimelineMessageIds.has(oldId) && !seenTimelineMessageIds.has(newId)) {
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seenTimelineMessageIds.delete(oldId)
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seenTimelineMessageIds.add(newId)
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setTimelineSegments((prev) => {
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const next = prev.map((segment) => {
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if (segment.messageId !== oldId) return segment
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const updatedId = segment.id.replace(oldId, newId)
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return { ...segment, messageId: newId, id: updatedId }
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})
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seenTimelineSegmentKeys.clear()
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next.forEach((segment) => seenTimelineSegmentKeys.add(makeTimelineKey(segment)))
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return next
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})
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// Keep part count tracking in sync with id replacement.
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const existingPartCount = timelinePartCountsByMessageId.get(oldId)
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if (existingPartCount !== undefined) {
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timelinePartCountsByMessageId.delete(oldId)
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timelinePartCountsByMessageId.set(newId, existingPartCount)
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if (previousTimelineIds.length === 0 && ids.length > 0) {
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seedTimeline()
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previousTimelineIds = [...ids]
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return
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}
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if (ids.length < previousTimelineIds.length) {
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seedTimeline()
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previousTimelineIds = [...ids]
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return
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}
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if (ids.length === previousTimelineIds.length) {
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let changedIndex = -1
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let changeCount = 0
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for (let index = 0; index < ids.length; index++) {
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if (ids[index] !== previousTimelineIds[index]) {
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changedIndex = index
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changeCount += 1
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if (changeCount > 1) break
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}
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}
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if (changeCount === 1 && changedIndex >= 0) {
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const oldId = previousTimelineIds[changedIndex]
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const newId = ids[changedIndex]
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if (seenTimelineMessageIds.has(oldId) && !seenTimelineMessageIds.has(newId)) {
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seenTimelineMessageIds.delete(oldId)
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seenTimelineMessageIds.add(newId)
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setTimelineSegments((prev) => {
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const next = prev.map((segment) => {
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if (segment.messageId !== oldId) return segment
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const updatedId = segment.id.replace(oldId, newId)
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return { ...segment, messageId: newId, id: updatedId }
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})
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seenTimelineSegmentKeys.clear()
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next.forEach((segment) => seenTimelineSegmentKeys.add(makeTimelineKey(segment)))
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return next
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})
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previousTimelineIds = ids.slice()
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return
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// Keep part count tracking in sync with id replacement.
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const existingPartCount = timelinePartCountsByMessageId.get(oldId)
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if (existingPartCount !== undefined) {
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timelinePartCountsByMessageId.delete(oldId)
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timelinePartCountsByMessageId.set(newId, existingPartCount)
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}
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previousTimelineIds = [...ids]
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return
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}
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}
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}
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}
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const newIds: string[] = []
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ids.forEach((id) => {
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if (!seenTimelineMessageIds.has(id)) {
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newIds.push(id)
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}
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})
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if (newIds.length > 0) {
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newIds.forEach((id) => {
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seenTimelineMessageIds.add(id)
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appendTimelineForMessage(id)
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const newIds: string[] = []
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ids.forEach((id) => {
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if (!seenTimelineMessageIds.has(id)) {
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newIds.push(id)
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}
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})
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}
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previousTimelineIds = ids.slice()
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if (newIds.length > 0) {
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newIds.forEach((id) => {
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seenTimelineMessageIds.add(id)
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appendTimelineForMessage(id)
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})
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}
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previousTimelineIds = [...ids]
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})
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})
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function clearPendingTimelinePartUpdateFrame() {
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@@ -886,36 +887,49 @@ export default function MessageSection(props: MessageSectionProps) {
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createEffect(() => {
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if (props.loading) return
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const ids = messageIds()
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const resolvedStore = store()
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// Also re-run when sessionRevision bumps (covers part additions within
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// existing messages) but read individual records inside untrack() to
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// avoid creating O(n) fine-grained subscriptions.
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sessionRevision()
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let hasChanges = false
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for (const messageId of ids) {
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const record = resolvedStore.getMessage(messageId)
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const partCount = record?.partIds.length ?? 0
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const previousCount = timelinePartCountsByMessageId.get(messageId)
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// Wrap the iteration in untrack() so that accessing individual elements
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// of the store-proxied `ids` array does not create O(n) per-element
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// reactive subscriptions. We only need to re-run when the memo
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// (messageIds) or sessionRevision changes — not per-element.
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untrack(() => {
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const resolvedStore = store()
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const idsSet = new Set(ids)
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let hasChanges = false
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if (previousCount === undefined) {
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timelinePartCountsByMessageId.set(messageId, partCount)
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continue
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for (const messageId of ids) {
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const record = resolvedStore.getMessage(messageId)
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const partCount = record?.partIds.length ?? 0
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const previousCount = timelinePartCountsByMessageId.get(messageId)
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if (previousCount === undefined) {
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timelinePartCountsByMessageId.set(messageId, partCount)
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continue
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}
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if (previousCount !== partCount) {
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timelinePartCountsByMessageId.set(messageId, partCount)
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pendingTimelineMessagePartUpdates.add(messageId)
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hasChanges = true
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}
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}
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if (previousCount !== partCount) {
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timelinePartCountsByMessageId.set(messageId, partCount)
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pendingTimelineMessagePartUpdates.add(messageId)
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hasChanges = true
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// Drop tracking for ids that are no longer present.
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// Use the Set for O(1) lookups instead of ids.includes() which is O(n).
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for (const trackedId of Array.from(timelinePartCountsByMessageId.keys())) {
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if (!idsSet.has(trackedId)) {
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timelinePartCountsByMessageId.delete(trackedId)
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}
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}
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}
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// Drop tracking for ids that are no longer present.
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for (const trackedId of Array.from(timelinePartCountsByMessageId.keys())) {
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if (!ids.includes(trackedId)) {
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timelinePartCountsByMessageId.delete(trackedId)
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if (hasChanges) {
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scheduleTimelinePartUpdateFlush()
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}
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}
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if (hasChanges) {
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scheduleTimelinePartUpdateFlush()
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}
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})
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})
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createEffect(() => {
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