Design TikTok - System Design | WinJob

Problem Statement and Short-Video Context

TikTok is a mobile-first short-form video product: vertical 9:16 clips (typically 15s–3min), an infinite For You Page (FYP) feed, and creation tools with licensed music, filters, duet, and stitch. Discovery is recommendation-driven—not search-first.

Interviewers test whether you separate upload/transcode (write-heavy, minutes-long pipelines) from feed serving (read-heavy, sub-200ms page budgets) and engagement telemetry (billions of swipe/complete/skip events per day).

Stakeholder	Pain	Lever
Viewer	Instant first frame on cellular	1–2s HLS segments + edge cache warming
Creator	Reliable publish on flaky LTE	Resumable multipart upload + async transcode
Trust	Viral harmful clips	Pre-amplification moderation scores

Verbalize scale: ~1B+ MAU class, hundreds of millions of DAU, peak evening swipe storms, and viral clips that spike like-count writes and CDN egress within minutes.

javaOne Dark Pro

1 public final class FeedSlo {
2   private final int maxPageMs;
3   public FeedSlo(int maxPageMs) { this.maxPageMs = maxPageMs; }
4   public boolean pageOk(long measuredMs) { return measuredMs <= maxPageMs; }
5 }

pythonOne Dark Pro

1 @dataclass(frozen=True)
2 class SwipeEvent:
3     user_id: str
4     video_id: str
5     watch_ratio: float
6     dwell_ms: int

typescriptOne Dark Pro

1 interface FypItem { videoId: string; rankScore: number; creatorId: string; }
2 export function shouldPrefetch(items: FypItem[], i: number, window: number): boolean {
3   return i < items.length - 1 && i >= items.length - window - 1;
4 }

Close: tie decisions to SLIs from sec-004 and capacity from sec-009–011.

Why interviewers care

TikTok interviews reward crisp scope, explicit trade-offs, and failure stories—not generic microservice diagrams.

Interview checkpoint

Name one failure story for Problem Statement and Short-Video Context that proves you understand real outages, not happy-path diagrams.

Key Highlights

•FYP-first discovery, not search-first
•Split upload path from feed read path
•Quantify swipe QPS before picking stores

1	public final class FeedSlo {
2	private final int maxPageMs;
3	public FeedSlo(int maxPageMs) { this.maxPageMs = maxPageMs; }
4	public boolean pageOk(long measuredMs) { return measuredMs <= maxPageMs; }
5	}

1	@dataclass(frozen=True)
2	class SwipeEvent:
3	user_id: str
4	video_id: str
5	watch_ratio: float
6	dwell_ms: int

1	interface FypItem { videoId: string; rankScore: number; creatorId: string; }
2	export function shouldPrefetch(items: FypItem[], i: number, window: number): boolean {
3	return i < items.length - 1 && i >= items.length - window - 1;
4	}

Problem Statement and Short-Video Context

Why interviewers care

Interview checkpoint

Key Highlights

Section Rescue Kit