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Search every question and quick fact in the course.

Everything, A to Z (283)

0.1 + 0.2 Quick fact · System design
412 vs 428 Quick fact · API design: REST, HTTP, GraphQL and gRPC
429, Retry-After and rate-limit headers Question · API design: REST, HTTP, GraphQL and gRPC
99.9% budget Quick fact · Observability and operations
A consistent error format Question · API design: REST, HTTP, GraphQL and gRPC
Access tokens, refresh tokens and rotation Question · Authentication and authorization
Advisory locks Question · Transactions, isolation and locking
An API for offline sync Question · Backends for mobile apps
API keys done right Question · Authentication and authorization
API performance on mobile networks Question · Backends for mobile apps
appendfsync everysec Quick fact · Caching and Redis
asyncio slow callbacks Quick fact · Concurrency in Python services
At-most-once, at-least-once and 'exactly once' Question · Distributed systems
Audit logs Question · Observability and operations
Authenticating service-to-service calls Question · Authentication and authorization
Autoscaling services Question · Performance and scaling
B-tree, GIN, GiST, BRIN and hash Question · SQL, indexing and PostgreSQL
Back-of-the-envelope estimates Question · System design
Backend for frontend (BFF) Question · Backends for mobile apps
Background job queues Question · Queues, Kafka and event-driven systems
Backpressure when consumers fall behind Question · Queues, Kafka and event-driven systems
Backups, RPO, RTO and multi-region Question · Cloud, deploys and infrastructure
Base62 length 7 Quick fact · System design
Batch and bulk endpoints Question · API design: REST, HTTP, GraphQL and gRPC
Batching database writes Question · Performance and scaling
bcrypt input limit Quick fact · Authentication and authorization
Blameless postmortems Question · Observability and operations
Blocking calls inside async code Question · Concurrency in Python services
Blue-green and canary releases Question · Cloud, deploys and infrastructure
Breached-password lookups Quick fact · Backend security
Broken object level authorization (BOLA) Question · Backend security
Burn rate 14.4 Quick fact · Observability and operations
Cache penetration and negative caching Question · Caching and Redis
Cache stampede on a hot key Question · Caching and Redis
Cache-aside: the default caching pattern Question · Caching and Redis
Cancellation and cleanup in asyncio Question · Concurrency in Python services
CancelledError Quick fact · Concurrency in Python services
Capacity with Little's law Question · Performance and scaling
Chaos experiments and failure testing Question · Testing backends
char(n) vs varchar vs text Quick fact · SQL, indexing and PostgreSQL
Choosing a database for a new service Question · NoSQL and choosing a database
Choosing HTTP status codes Question · API design: REST, HTTP, GraphQL and gRPC
Choosing Redis data structures Question · Caching and Redis
Circuit breakers and bulkheads Question · Distributed systems
Clocks, timestamps and ordering events Question · Distributed systems
Cloud metadata IP Quick fact · Backend security
Column order in a composite index Question · SQL, indexing and PostgreSQL
Committing offsets: at-most-once vs at-least-once Question · Queues, Kafka and event-driven systems
Compressing API responses Question · Performance and scaling
Configuration across environments Question · Cloud, deploys and infrastructure
Connection pooling and PgBouncer Question · SQL, indexing and PostgreSQL
Consensus and Raft Question · Distributed systems
Consistency models from strong to eventual Question · Distributed systems
Consistent hashing Question · Distributed systems
Consumer groups and rebalancing Question · Queues, Kafka and event-driven systems
Consumers vs partitions Quick fact · Queues, Kafka and event-driven systems
Containers and images Question · Cloud, deploys and infrastructure
Contract testing between services Question · Testing backends
Cookie flags for session security Question · Authentication and authorization
Coordinated omission Quick fact · Performance and scaling
COPY Quick fact · Performance and scaling
CORS isn't CSRF protection Quick fact · Backend security
CORS: what it protects and how to configure it Question · API design: REST, HTTP, GraphQL and gRPC
CPU limits throttle Quick fact · Cloud, deploys and infrastructure
CQRS and read models Question · Distributed systems
Credential stuffing and brute force Question · Backend security
CSRF and how cookies cause it Question · Backend security
Dead-letter queues and poison messages Question · Queues, Kafka and event-driven systems
deadlock_timeout Quick fact · Transactions, isolation and locking
Deadlocks and lock ordering Question · Transactions, isolation and locking
Deadlocks with application locks Question · Concurrency in Python services
Default isolation in PostgreSQL Quick fact · Transactions, isolation and locking
Default maxmemory-policy Quick fact · Caching and Redis
Dependency and supply-chain security Question · Backend security
Design a chat backend Question · System design
Design a distributed rate limiter Question · System design
Design a news feed Question · System design
Design a payment flow Question · System design
Design a URL shortener Question · System design
Design file uploads and storage Question · System design
Design search autocomplete Question · System design
Designing reliable webhooks Question · API design: REST, HTTP, GraphQL and gRPC
Designing REST resources Question · API design: REST, HTTP, GraphQL and gRPC
Detecting failures and avoiding split brain Question · Distributed systems
Distributed tracing Question · Observability and operations
Document store or relational database? Question · NoSQL and choosing a database
Embedding vs referencing in MongoDB Question · NoSQL and choosing a database
Encryption in transit and at rest Question · Backend security
Errors inside a transaction Question · Transactions, isolation and locking
ETags and conditional requests Question · API design: REST, HTTP, GraphQL and gRPC
Event sourcing Question · Queues, Kafka and event-driven systems
Eviction: LRU, LFU and maxmemory Question · Caching and Redis
Evolving event schemas Question · Queues, Kafka and event-driven systems
Expand and contract changes Question · Cloud, deploys and infrastructure
Fakes, stubs and mocks Question · Testing backends
Feature flags on the server Question · Cloud, deploys and infrastructure
Fencing token Quick fact · Distributed systems
Finding where time goes Question · Performance and scaling
Flaky tests Question · Testing backends
Free-threaded Python Quick fact · Concurrency in Python services
Google Play acknowledgement Quick fact · Backends for mobile apps
Graceful shutdown Question · Cloud, deploys and infrastructure
gRPC vs REST Question · API design: REST, HTTP, GraphQL and gRPC
Gunicorn starting point Quick fact · Concurrency in Python services
hmac.compare_digest Quick fact · Backend security
Hot keys and hot partitions Question · Performance and scaling
How a B-tree index speeds up a query Question · SQL, indexing and PostgreSQL
How asyncio works Question · Concurrency in Python services
HTTP caching headers Question · Caching and Redis
HTTP security headers Question · Backend security
HyperLogLog Quick fact · Caching and Redis
Hypothesis Quick fact · Testing backends
Idempotency keys for POST Question · API design: REST, HTTP, GraphQL and gRPC
Idempotent consumers and deduplication Question · Queues, Kafka and event-driven systems
Idempotent methods Quick fact · API design: REST, HTTP, GraphQL and gRPC
Idempotent producer Quick fact · Queues, Kafka and event-driven systems
Identity columns Quick fact · SQL, indexing and PostgreSQL
Implicit flow Quick fact · Authentication and authorization
Index-only scans and INCLUDE Question · SQL, indexing and PostgreSQL
India offset Quick fact · Backends for mobile apps
Infrastructure as code Question · Cloud, deploys and infrastructure
integer range Quick fact · SQL, indexing and PostgreSQL
Integration tests with a real database Question · Testing backends
Isolation levels in PostgreSQL Question · Transactions, isolation and locking
JSON Merge Patch Quick fact · API design: REST, HTTP, GraphQL and gRPC
JSON pitfalls: money, big ids and dates Question · API design: REST, HTTP, GraphQL and gRPC
JSONB in PostgreSQL Question · NoSQL and choosing a database
jsonb vs json Quick fact · NoSQL and choosing a database
JWT payloads Quick fact · Authentication and authorization
Kafka 4 Quick fact · Queues, Kafka and event-driven systems
Kafka exactly-once Quick fact · Distributed systems
Kafka or RabbitMQ? Question · Queues, Kafka and event-driven systems
Kafka ordering Quick fact · Queues, Kafka and event-driven systems
Kafka partitions, keys and ordering Question · Queues, Kafka and event-driven systems
Keeping a cache consistent with the database Question · Caching and Redis
Keeping messages in order Question · Queues, Kafka and event-driven systems
Keeping secrets and personal data out of logs Question · Observability and operations
Kubernetes basics for backend developers Question · Cloud, deploys and infrastructure
Kubernetes grace period Quick fact · Cloud, deploys and infrastructure
Largest safe JavaScript integer Quick fact · API design: REST, HTTP, GraphQL and gRPC
Layering a backend service Question · System design
Leader election, leases and fencing tokens Question · Distributed systems
Leader-follower replication and lag Question · Distributed systems
LIMIT without ORDER BY Quick fact · SQL, indexing and PostgreSQL
Limiting concurrency with semaphores Question · Concurrency in Python services
Little's law Quick fact · Performance and scaling
Liveness and readiness checks Question · Observability and operations
Load balancing strategies Question · Performance and scaling
Load testing a backend Question · Performance and scaling
Locks in Redis: when they're safe Question · Distributed systems
Long-running operations: 202 and polling Question · API design: REST, HTTP, GraphQL and gRPC
lru_cache default Quick fact · Performance and scaling
Majority sizes Quick fact · Distributed systems
Managing secrets Question · Backend security
Mass assignment Question · Backend security
Mean vs tail Quick fact · Performance and scaling
Memory growth in Python services Question · Performance and scaling
Metrics and label cardinality Question · Observability and operations
MFA and TOTP codes Question · Authentication and authorization
Minimum supported app versions Question · Backends for mobile apps
Modulo resharding Quick fact · Distributed systems
MongoDB document limit Quick fact · NoSQL and choosing a database
Monitoring consumer lag Question · Queues, Kafka and event-driven systems
Monolith or microservices Question · System design
Monotonic time Quick fact · Distributed systems
MVCC, dead tuples and VACUUM Question · Transactions, isolation and locking
no-cache vs no-store Quick fact · Caching and Redis
Normalization and when to denormalize Question · SQL, indexing and PostgreSQL
NULL, three-valued logic and NOT IN Question · SQL, indexing and PostgreSQL
OAuth 2.0 authorization code with PKCE Question · Authentication and authorization
Object storage for files Question · NoSQL and choosing a database
OFFSET vs keyset pagination Question · SQL, indexing and PostgreSQL
OpenID Connect and ID tokens Question · Authentication and authorization
Optimistic vs pessimistic locking Question · Transactions, isolation and locking
OWASP API #1 Quick fact · Backend security
PACELC Quick fact · Distributed systems
Paginating API responses Question · API design: REST, HTTP, GraphQL and gRPC
Partial and expression indexes Question · SQL, indexing and PostgreSQL
Partition keys in DynamoDB-style stores Question · NoSQL and choosing a database
Partitioner difference Quick fact · Queues, Kafka and event-driven systems
PATCH: merge patch vs JSON Patch Question · API design: REST, HTTP, GraphQL and gRPC
PKCE verifier length Quick fact · Authentication and authorization
Points per day Quick fact · NoSQL and choosing a database
Polling, SSE and WebSockets Question · API design: REST, HTTP, GraphQL and gRPC
Postgres now() Quick fact · Testing backends
Producer-consumer with asyncio.Queue Question · Concurrency in Python services
Property-based testing Question · Testing backends
Queue.shutdown Quick fact · Concurrency in Python services
Quorum reads and writes Question · Distributed systems
Race conditions in async code Question · Concurrency in Python services
Rate limiting with a token bucket Question · API design: REST, HTTP, GraphQL and gRPC
RBAC, ABAC and resource ownership Question · Authentication and authorization
Reading EXPLAIN ANALYZE Question · SQL, indexing and PostgreSQL
Recursive CTE cycles Quick fact · NoSQL and choosing a database
RED Quick fact · Observability and operations
RED and USE dashboards Question · Observability and operations
Redis Cluster slots Quick fact · Caching and Redis
Redis durability: RDB, AOF and when Redis is a database Question · Caching and Redis
Redis pub/sub Quick fact · Queues, Kafka and event-driven systems
Replicas aren't backups Quick fact · Cloud, deploys and infrastructure
Request-scoped context with contextvars Question · Concurrency in Python services
Retries with exponential backoff and jitter Question · Distributed systems
Retrying serialization failures Question · Transactions, isolation and locking
Revoking tokens and sessions Question · Authentication and authorization
RFC 6238 vector Quick fact · Authentication and authorization
RFC 9457 Quick fact · API design: REST, HTTP, GraphQL and gRPC
Row order Quick fact · Testing backends
RPO and RTO Quick fact · Cloud, deploys and infrastructure
Running an incident Question · Observability and operations
S3 consistency Quick fact · NoSQL and choosing a database
S3 durability Quick fact · NoSQL and choosing a database
S3 multipart limits Quick fact · API design: REST, HTTP, GraphQL and gRPC
Safe and idempotent HTTP methods Question · API design: REST, HTTP, GraphQL and gRPC
Sagas: orchestration vs choreography Question · Distributed systems
Scaling a cache cluster and hot keys Question · Caching and Redis
Scaling reads with replicas Question · Performance and scaling
Scaling up vs scaling out Question · Performance and scaling
Scheduled jobs that run once Question · Queues, Kafka and event-driven systems
Schema changes without downtime Question · SQL, indexing and PostgreSQL
Search with Elasticsearch or OpenSearch Question · NoSQL and choosing a database
Seconds in a month Quick fact · System design
SELECT FOR UPDATE and SKIP LOCKED Question · Transactions, isolation and locking
Sending push notifications at scale Question · Backends for mobile apps
Server sessions vs stateless tokens Question · Authentication and authorization
Server-side request forgery (SSRF) Question · Backend security
Serving images to mobile apps Question · Backends for mobile apps
Sharding: range, hash and directory Question · Distributed systems
Sharing state between threads safely Question · Concurrency in Python services
Signing requests and webhooks with HMAC Question · Backend security
SLOs, error budgets and alerts Question · Observability and operations
Spreading expiries with TTL jitter Question · Caching and Redis
SQL injection and parameterised queries Question · Backend security
SQLSTATE 25P02 Quick fact · Transactions, isolation and locking
SQLSTATE 40001 Quick fact · Transactions, isolation and locking
Storing passwords Question · Authentication and authorization
Storing time-series data Question · NoSQL and choosing a database
Strangler fig Quick fact · System design
Structured logging Question · Observability and operations
TaskGroup Quick fact · Concurrency in Python services
TaskGroup vs gather Question · Concurrency in Python services
Template databases Quick fact · Testing backends
Test data and fixtures Question · Testing backends
Testing code that uses time and randomness Question · Testing backends
Testing database migrations Question · Testing backends
The GIL, threads and processes Question · Concurrency in Python services
The lost update problem Question · Transactions, isolation and locking
The N+1 query problem Question · SQL, indexing and PostgreSQL
The test pyramid for a backend Question · Testing backends
The transactional outbox pattern Question · Distributed systems
Time zones and timestamps Question · Backends for mobile apps
Timeouts and deadline propagation Question · Distributed systems
timestamptz Quick fact · Backends for mobile apps
Token introspection Quick fact · Authentication and authorization
traceparent Quick fact · Observability and operations
Transaction ids Quick fact · Transactions, isolation and locking
TTL jitter in our run Quick fact · Caching and Redis
Two-phase commit and why services avoid it Question · Transactions, isolation and locking
Uploading large files Question · API design: REST, HTTP, GraphQL and gRPC
Upserts with ON CONFLICT Question · SQL, indexing and PostgreSQL
US DST end 2026 Quick fact · Backends for mobile apps
USE Quick fact · Observability and operations
UUIDv7 Quick fact · SQL, indexing and PostgreSQL
Validating a JWT properly Question · Authentication and authorization
Verifying in-app purchases on the server Question · Backends for mobile apps
Versioning an API Question · API design: REST, HTTP, GraphQL and gRPC
What ACID really promises Question · Transactions, isolation and locking
What an API gateway does Question · API design: REST, HTTP, GraphQL and gRPC
What CAP actually says Question · Distributed systems
What to put behind a CDN Question · Caching and Redis
When a graph database helps Question · NoSQL and choosing a database
When GraphQL fits and what it costs Question · API design: REST, HTTP, GraphQL and gRPC
When serverless fits Question · Cloud, deploys and infrastructure
Where transactions begin and end in code Question · Transactions, isolation and locking
Which API changes are breaking Question · API design: REST, HTTP, GraphQL and gRPC
Why long transactions hurt Question · Transactions, isolation and locking
Why percentiles, not averages Question · Performance and scaling
Wide-column stores like Cassandra Question · NoSQL and choosing a database
Window functions Question · SQL, indexing and PostgreSQL
Work queues vs publish/subscribe Question · Queues, Kafka and event-driven systems
Write skew under REPEATABLE READ Question · Transactions, isolation and locking
Write-through, write-behind and write-around Question · Caching and Redis
WSGI vs ASGI servers Question · Concurrency in Python services
XSS from a backend's point of view Question · Backend security