Intermediate interview questions in Backend Dev, page 10
When a graph database beats relational or document stores
Deeply connected data, variable-depth traversals, fraud or recommendation paths, index-free adjacency.
Static dispatch over Write with generics in Rust
Write generically over the std::io::Write trait with a type parameter W: Write, letting the compiler monomorphize and inline per concrete type, avoiding the vtable indirection of Box<dyn Write>.
How do you authenticate a FastAPI WebSocket connection?
This tests WebSocket limits and FastAPI dependency injection. Pass the JWT via query parameter or cookie at handshake, validate it with Depends, and reject with HTTP 403 or 1008 close.
How to sync state across multiple user devices?
Attach userId to each socket, track active sockets per user, broadcast user state to all their sockets.
WebSocket connection manager and broadcast
A manager class holding a list of active connections, connect accepts and appends, disconnect removes, broadcast iterates sending to each, all wrapped in try/finally to handle disconnects.
Choosing a good shard key and avoiding hot spots
High cardinality, even write distribution, query alignment; monotonic keys send all writes to one shard.
Using context.Context across microservice calls in Go
Context carries cancellation, deadlines, and values; pass ctx as first arg, set one WithTimeout at the edge, attach a request ID via WithValue, thread it through downstream calls so all cancel…
Synchronous vs asynchronous replication trade-offs
Sync waits for replica ack giving zero data loss but higher latency; async acks immediately, faster but risks losing recent writes on failover.
Rust Send and Sync marker traits explained
Send means a value can move across threads, Sync means a reference can be shared; Rc uses non-atomic refcounts, Arc uses atomic ones.
The N+1 query problem and how to fix it
One query for a list plus one per item for its relation, fix with eager loading or a batched join.
Tuning a database connection pool
Max size, min idle, connection and max-lifetime timeouts; size from cores and latency, not guesswork.
Upgrading a stateful Flink job without losing state
Take a savepoint, stop with drain, deploy new jar, restore from savepoint with matching operator UIDs.
Fearless concurrency: Rust compile-time vs Go runtime
Rust uses ownership plus Send/Sync to reject data races at compile time; Go encourages channels but still allows races, with the runtime race detector catching them at test…
Denormalization: trading write cost for read speed
Duplicate or precompute data to avoid joins, accept harder writes and consistency risk, justify by read-heavy access.
Rust lifetimes versus Go garbage-collected lifetimes
A lifetime is a compile-time region a reference is valid for; annotations like 'a relate input and output reference durations; Go instead uses garbage collection and escape analysis.
What are key Dockerfile steps for Node.js Express apps?
Use lightweight base image, copy app, install deps, expose port, set NODE_ENV, run.
Predicate pushdown and why it speeds queries
Apply WHERE conditions at the scan or remote source, prune partitions and rows early, shrink data movement.
Criterion: the standard Rust benchmarking library
Criterion runs on stable Rust, collects many samples, applies statistical analysis with confidence intervals, and compares against saved baselines to detect regressions.
What are the key responsibilities for Nginx versus Uvicorn?
This tests the reverse-proxy versus ASGI-server boundary. A strong answer gives Nginx TLS termination, static files, buffering, and load balancing, while Uvicorn runs the Python app and async workers.
dependencies vs devDependencies in production?
Dependencies are needed at runtime, devDependencies only for development. npm install includes both, npm ci --only=production excludes dev.
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