Meta · senior product engineering

Your worked rehearsal: deliver notifications while preserving preferences and recovery

When Alice posts, Bob may receive an inbox item if he opted in. Alice’s Save must not wait for every follower’s inbox write, and a repeated queue delivery must not create duplicate inbox items. A push notification is a separate external delivery that may already be on a device.

Design durable acceptance and an inbox update first. Then introduce a large sender, queue delay, and privacy changes. The session uses constructed product requirements and does not claim to match Meta’s production services.

Starting point: these drills are build briefs. Implement in a local file or draw the requested architecture. The worked answer is an explanation, not a supplied end-to-end application. Choose one drill per session, then change one requirement after the baseline works.

Meta's published full-loop guide describes coding, system/product design, and behavioral conversations, generally 45 minutes each in a four-to-six-interview loop. It discusses solving two coding problems in roughly 40 minutes and evaluating communication, problem solving, and verification. A self-reported E5 infrastructure account from within the past year describes tree/graph and array/string coding, a staged AI coding exercise, design, and behavioral rounds. Infra is not product; that report is a single anecdote, not a general Meta E5 blueprint.

The room · time-boxed clarity

How it may feel: little time to spend on an elaborate preamble. State constraints, choose an invariant, write executable code, and walk through a boundary test. On design, give the client-to-storage story first, then zoom into the highest-risk decision. This describes preparation for the official format; the specific questions below are not a verified “most asked” list.

Ask first: Is this a product architecture or large-scale system design round? Can you run code? What inputs are promised? Is the AI exercise present, and what tools are permitted?

Choose a coding exercise · eight original drills

The first three mirror categories in one E5 infra report, not its exact prompts; the remainder are original practice.

Choose an architecture exercise · five original prompts

Worked session · notification fanout

Interviewer: “When someone posts, notify their followers. Design a product API and service for ordinary and very large accounts. What does a user see if they were offline?”

Clarify aloud: Is a notification required for every post or only opted-in accounts? Exactly-once display or at-least-once delivery? What is the retention period? Assume per-recipient opt-in, eventually visible inbox, 30-day retention, and idempotency key (post_id, recipient_id, channel).

Think in public: a synchronous loop on the post-write path couples latency to follower count. Write the post and an outbox event transactionally; consume with idempotent inbox writes. Segment high-degree senders: fanout-on-read or hybrid only when it beats precomputation, with a clear freshness contract. Distinguish inbox item identity from push delivery attempt.

Follow-up 1 (senior): “The notification queue is six hours behind.” Prioritize recent/interactive traffic, cap retries, expose lag, and make the inbox serve the durable source rather than claim eventual processing is instantaneous. Follow-up 2 (staff): “A privacy deletion crosses regions while push has already gone out.” Specify what can be recalled, enforce checks before new deliveries, build deletion propagation and audit metrics; avoid promising retractable push notifications.

Worked extension: isolate urgent work from a six-hour backlog

A single FIFO backlog can make a fresh reply notification wait behind old bulk work. Define classes from product requirements, apply bounded admission, and allocate processing capacity. Do not simply relabel every delayed item “urgent”. At 500 useful writes/s and 350 new writes/s, only 150/s remains for catch-up. A backlog of 90,000 items takes at least ten minutes under those constant-rate assumptions.

Recheck permission before new delivery. A deletion can remove an inbox item or suppress a pending push, but cannot guarantee recall of content already displayed by another device. Name that limit in both the product response and recovery plan.

Evidence: Official Meta guide (undated PDF; verify with recruiter) and one E5 infrastructure candidate account (self-report within a year). The exercises are original, checked 22 September 2026.