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Meta·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say
Apr 2026

Summary

Meta system design screen focused heavily on database fundamentals, specifically transactions and concurrency. More theoretical than I expected for a coding round, but it made sense in hindsight given the scale Meta operates at.

Questions Asked (1)

Q1

Walk me through what a database transaction is, explain the ACID properties, and describe the standard transaction isolation levels including what anomalies each one prevents or allows.

System DesignTechnical Trade-offsData Modeling
Author's notes

This is one of those questions where you think you know it cold and then freeze on the details.

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AI HintsAI Generated

Suggested Approach

Start by defining a database transaction as a unit of work that must be atomic, then explain ACID properties with concrete examples. Next, describe the four standard isolation levels (Read Uncommitted, Read Committed, Repeatable Read, Serializable) and for each, list the anomalies they prevent or allow (dirty reads, non-repeatable reads, phantom reads). Finally, tie it back to practical trade-offs in system design, such as performance vs. consistency.

Pro tip: Mention that isolation levels are often implemented using locking or MVCC, and that the SQL standard's definitions are not always strictly followed by databases (e.g., Oracle's Read Committed prevents phantoms). This shows depth beyond textbook knowledge.

1. Define Transaction

Explain that a transaction is a sequence of operations performed as a single logical unit of work, with the goal of maintaining data integrity.

2. Explain ACID

Describe each property: Atomicity (all or nothing), Consistency (valid state transitions), Isolation (concurrent transactions don't interfere), Durability (committed changes persist).

3. List Isolation Levels

Name the four standard levels: Read Uncommitted, Read Committed, Repeatable Read, Serializable, and briefly define each.

4. Map Anomalies to Levels

For each isolation level, state which anomalies (dirty read, non-repeatable read, phantom read) are prevented or allowed, using a table-like summary.

5. Discuss Trade-offs

Explain that higher isolation increases consistency but reduces concurrency and performance, and mention real-world implementations like MVCC.

Key Points to Mention

  • Atomicity: transaction is all-or-nothing; rollback on failure.
  • Consistency: transaction brings database from one valid state to another, preserving constraints.
  • Isolation: concurrent transactions appear serial; levels control visibility of uncommitted changes.
  • Durability: once committed, changes survive system failures (e.g., via write-ahead logging).
  • Anomalies: dirty read (reading uncommitted data), non-repeatable read (same query returns different data), phantom read (new rows appear in range query).
  • Isolation levels: Read Uncommitted (allows dirty, non-repeatable, phantom), Read Committed (prevents dirty, allows non-repeatable and phantom), Repeatable Read (prevents dirty and non-repeatable, allows phantom), Serializable (prevents all).

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.