CQRS & Event Sourcing

Separates read models from write models (CQRS) and stores business state as an immutable append-only sequence of domain events rather than mutating rows in-place.

STAFF ENGINEER TAKEAWAY: Never overwrite historical data; appending immutable events allows point-in-time replay, complete audit logs, and independent read/write database scaling.

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More Topics in 3. Data & Storage

🗄️SQL Relational vs NoSQL Engines

SQL databases enforce structured schemas and ACID transactions with relations. NoSQL systems optimize for flexible schemas, horizontal partition scale, and eventual consistency.

🌲B-Tree & B+Tree Indexing

Self-balancing search tree data structure that keeps data sorted and allows searches, sequential access, insertions, and deletions in logarithmic O(log N) time.

🏛️ACID Transactions & Isolation Levels

Guarantees Atomicity (all-or-nothing), Consistency (rules preserved), Isolation (concurrent safety), and Durability (WAL commits survive power loss).

🔺CAP Theorem (Consistency vs Availability)

In any distributed data store, network partitions (P) are inevitable. When a partition occurs, the system must choose between Consistency (CP) or Availability (AP).