Easy everything in Backend Dev, page 4
Purpose of the Write-Ahead Log
WAL records changes sequentially and is flushed to disk before commit; the rule is log first, then data pages may lag; on crash the database replays the log to recover committed work.
What is a database page?
A page is a fixed-size block, often 8KB, holding multiple rows; databases read and write whole pages because disk and OS I/O are block-oriented, amortizing seek cost and matching the buffer pool unit.
Clustered versus non-clustered indexes
A clustered index orders the table's actual rows, one per table; a non-clustered index is a separate structure pointing to rows.
Composite index column order for multi-column filters
Create one index on (last_name, first_name); order matters because the index serves leftmost-prefix lookups.
What a database index is and when it helps
An index is a sorted lookup structure avoiding full scans, helps selective WHERE/JOIN columns, but costs write overhead.
Database deadlocks and how engines resolve them
Define a deadlock as mutual waiting on locks, name detection plus victim rollback, and prevention by consistent lock ordering.
The lost update anomaly explained
Both transactions read the same value, each adds one, the second overwrite erases the first.
The ACID properties of transactions
Define Atomicity, Consistency, Isolation, Durability and why each matters.
Modeling one-to-many versus many-to-many relationships
One-to-many uses a foreign key on the many side; many-to-many needs a junction table with two foreign keys.
Normalizing a flat orders table to 3NF
Split repeating data, remove partial dependencies, remove transitive dependencies, define keys.
In-memory rate limiter middleware in Go
Use a token-bucket limiter (golang.org/x/time/rate), guard a per-client map with sync.Mutex, wrap http.Handler so requests over the limit get 429.
Handling Result and errors in a Rust web handler
Handler returns Result, the ? operator early-returns errors, a custom error type implements IntoResponse to map to 500, success returns 200 with data.
Structuring a Go CLI that fetches a URL
Parse args with the flag package, http.Get the URL, check err and status, defer resp.Body.Close, copy body to stdout, exit non-zero on failure.
Refactoring under Go simplicity versus Rust correctness
Rust's type system catches broken invariants at compile time so refactors are guided; Go's explicitness keeps code readable but shifts safety to tests and discipline.
Implicit Interface Satisfaction in Go
Go types satisfy an interface automatically by having the right methods, with no explicit implements declaration. This structural typing decouples implementations from interface definitions, so you can define interfaces around how you use a type without…
Why use an ASGI server like Uvicorn instead of the dev server?
Tests: dev vs prod environment distinction. Answer: Uvicorn is a prod server program; contrast dev server's constant restart/break/fix cycle with prod needs for performance, stability, and uninterrupted access.
Walk me through a basic Dockerfile for a FastAPI app
Slim base, install deps before app code to cache layers, expose port, exec-form CMD for Uvicorn.
What are startup and shutdown events in FastAPI?
Tests app lifespan hooks and resource lifecycle. Startup creates DB pools before traffic arrives; shutdown closes them after the last request. These decorators are deprecated; prefer lifespan context managers. Red flag: per-request middleware.
How do you define a WebSocket endpoint in FastAPI?
Import WebSocket, use @app.websocket, await accept, receive_text, then send_text.
What are FastAPI's two default interactive documentation UIs and URL paths?
This tests whether you know FastAPI's built-in auto-generated docs. A strong answer names Swagger UI at /docs and ReDoc at /redoc, then notes the OpenAPI schema at /openapi.json. A weak answer confuses these with external tools or custom routes.
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