Interview questions in Backend Dev, page 12
What is the difference between OLTP and OLAP?
OLTP handles many short read-write transactions on normalized current data; OLAP runs few large analytical scans over denormalized historical data.
Sharing mutable state: Go mutex vs Rust Arc Mutex
Go uses sync.Mutex by convention; Rust wraps data in Arc<Mutex<T>> so locking is mandatory, enforced by Send/Sync and the borrow checker.
How do you safely execute blocking code from an async function
Tests whether you know how to prevent event loop blocking by offloading sync work. Name asyncio.to_thread or run_in_executor, explain ThreadPoolExecutor scheduling, and note when processes beat threads.
API versioning: URL vs header strategies
Version via URL path (/v1/), a custom or Accept header, or a query param; URL is visible and cache-friendly, headers keep URLs clean but are less discoverable.
What is a star schema?
A central fact table of measures and foreign keys surrounded by denormalized dimension tables of descriptive attributes, joined in one hop for fast, simple analytical queries.
Rust async/await vs Go goroutines
Go schedules goroutines on a built-in runtime transparently; Rust futures are inert until polled by an external runtime like Tokio, and async colors functions.
Explain the asyncio event loop and cooperative multitasking
Tests if you view the event loop as a single-threaded orchestrator, not magic parallelism. Strong answers note it runs tasks and callbacks, manages a ready queue, and yields control at await. Red flag: calling it multithreading or parallel execution.
asyncio.gather vs asyncio.wait
Gather returns ordered results and propagates the first exception (or captures them); wait returns done/pending sets and never raises, you inspect each.
Define a Mongoose schema and model
New mongoose.Schema with field options (type, required, default), then mongoose.model('Product', schema) to get a model.
What is the difference between ETL and ELT?
ETL transforms before loading, on a separate engine; ELT loads raw then transforms inside a scalable warehouse. Choose ELT with cloud warehouses and large raw or schema-on-read data.
What is Go's context package and how do you use WithCancel?
This tests cancellation propagation. A good answer says Context carries deadlines, signals; derive a child with WithCancel, pass it to worker, then call cancel to unblock ctx.Done. Bad: storing context in structs, leaking cancel functions, or ignoring Done.
Mongoose populate() for referenced documents
Populate() replaces stored ObjectIds with the referenced documents, needs a ref in the schema, called via .populate('author').
Star schema vs snowflake schema trade-offs?
Star keeps dimensions denormalized for fewer joins and faster simpler queries; snowflake normalizes dimensions into sub-tables saving space and easing maintenance but adding joins.
When should you use asyncio.Lock over threading.Lock?
This tests cooperative multitasking knowledge: asyncio.Lock yields to the event loop via await, while threading.Lock blocks the OS thread and freezes the loop. A red flag is claiming threading.Lock works because locks are universal.
Go select vs Rust select! fairness and determinism
This tests runtime fairness in concurrent primitives. Contrast Go's pseudo-random case selection with Tokio's randomized default and its opt-in biased; top-down mode. Red flag: claiming Go uses source order or that Rust randomization is unavoidable.
Database migrations with the Sequelize CLI
Migrations are version-controlled scripts with up/down so teams apply identical schema changes; use sequelize-cli to generate, edit with addColumn, then db:migrate.
How does columnar storage speed up analytics?
Columnar stores each column contiguously, so aggregations read only needed columns, scan far less data, and compress better with vectorized execution.
Unhandled exception in asyncio.create_task(): consequence and detection
Tests Task exception capture vs propagation. Good answer: exceptions are stored in the Task object, the loop keeps running, and the creator must await the task or call task.exception() to retrieve it; unretrieved ones may be logged.
When should Rust atomics replace a Mutex, and how do orderings work?
Atomics replace mutexes for counters; Relaxed is atomicity only, SeqCst adds global order, weaker ones skip fences on ARM.
Mongoose pre('save') hooks for password hashing
Pre('save') runs before persistence; use it to hash the password, guarding with isModified, calling next() or returning.
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