Search the practice set
275 questions, 991 terms and 600 topics in 30 areas.
60 results for “Partition Keys & Ordering”
Key Skew
An uneven distribution of records across partitions, which caps throughput at the busiest partition regardless of how many exist.
Message Ordering
The guarantee about the sequence in which messages are delivered — normally per-partition or per-group only, and lost the moment consumption is parallelised.
Partition Assignment
The mapping of partitions to consumer instances that determines parallelism, ordering guarantees and what happens when the consumer set changes.
A/B Partition Update
Writing firmware to an inactive partition and switching on next boot, so a failed update falls back to the previous image rather than bricking the device.
Hot Partition
One partition receiving disproportionate traffic, so the system saturates at a fraction of its aggregate capacity.
Partition Pruning
The query planner skipping files whose partition values cannot satisfy the predicate, which is the single largest determinant of analytical query cost.
Partition Tolerance
The ability to keep operating when the network drops or delays messages between nodes — not a choice, but a property of any system spanning more than one machine.
AI Gateway
A shared proxy in front of model providers that centralises routing, keys, quotas, caching, logging and safety policy.
Bloom Filter Cache Guard
Placing a Bloom filter in front of an expensive lookup so that keys which certainly do not exist never reach it.
CAP Theorem
During a network partition a distributed system must choose between consistency and availability; it cannot have both.
Cache Penetration
Repeated lookups for keys that do not exist, which miss the cache every time by definition and pass straight through to the store.
Causal Consistency
A model guaranteeing that operations which causally depend on one another are seen in the same order everywhere, while concurrent operations may be seen in any order.
Clock Drift
Device clocks diverging from real time, which corrupts ordering, expires certificates early or late, and produces data that appears to arrive from the past.
Consistent Hashing
A hashing scheme where adding or removing a node remaps only a small fraction of keys, instead of nearly all of them.
Consistent Prefix Read
A guarantee that if a sequence of writes happens in a given order, a reader sees a prefix of that sequence — never an out-of-order subset.
Consumer Group
A set of consumers that cooperatively read one stream, with each partition assigned to exactly one member, so the group collectively processes every message once.
Discord's Message Store Migrations
Discord moved from MongoDB to Cassandra to ScyllaDB as message volume grew from millions to trillions, each time for a specific and different reason.
Encryption at Rest and in Transit
Protecting stored data from disclosure if the medium is obtained, and network data from disclosure if the path is observed — two different controls against two different threats.
Envelope Encryption
Encrypting data with a locally-generated data key, then encrypting that key with a master key held in a key management service, and storing the wrapped key alongside the ciphertext.
Hardware Security Module
A tamper-resistant device that generates and stores keys and performs cryptographic operations without the key material ever being extractable.
Hub and Satellite
Separating stable business keys from their changing attributes and from their relationships, so each can be loaded independently and kept forever.
Idempotency Scope
The boundary within which an idempotency key is unique and meaningful — per account, per endpoint, or global — and the retention window it lives for.
Idempotency Token Store
The durable record of which idempotency keys have been seen and what each one returned, and the component that decides whether the guarantee is real.
JWKS
A published endpoint listing an issuer's current public keys, allowing resource servers to validate token signatures without a shared secret and to survive key rotation.
Key Rotation
Periodically replacing a cryptographic key with a new one while retaining the old for decrypting existing data, so exposure from any single key is bounded.
Keyed State Size
The total state a job holds per key across all keys, which governs memory, checkpoint duration and recovery time.
Pipeline Fan-Out
Splitting independent verification work to run in parallel, bounded by what genuinely has no ordering dependency on anything else.
Pivot Transaction
The step in a saga after which the transaction can no longer be cancelled — everything before it is compensatable, everything after it is retriable until it succeeds.
Poison Message
A record that a consumer cannot process and cannot skip, which halts its partition entirely until someone intervenes.
Shard Key Selection
Choosing the attribute that determines a record's partition, which fixes the system's distribution, query patterns and future flexibility.
Sharding
Splitting one dataset across multiple independent databases by a partition key, so that each holds a disjoint subset.
Split Brain
A partition in which two halves of a cluster each believe they are authoritative, and both accept writes.
Surrogate Key
A system-generated identifier with no business meaning, used as the primary key instead of a naturally occurring business value.
Version Vector
A per-replica counter set that lets a system tell whether one version causally descends from another or whether the two are genuinely concurrent.
A 43-second network partition caused GitHub over 24 hours of degraded service in 2018. How does a 43-second event become a day-long incident?
The case, as publicly reported On 21 October 2018, routine maintenance replacing failing optical equipment caused a 43 second loss of connectivity between GitHu
A card payment authorisation service runs active-active across two regions. A network partition splits them. Do you keep accepting authorisations, and what breaks either way?
What the interviewer is testing Whether you can apply CAP to a domain where the cost of each choice is concrete, and whether you recognise that "it depends" has
A multi-tenant SaaS product has outgrown one database. You must shard. How do you choose the partition key, and what makes this decision so expensive to get wrong?
What the interviewer is testing Whether you exhaust cheaper options first, and whether you understand that a shard key is close to irreversible. First: do not s
Discord stores trillions of messages. What is their partition key, and what problem does the second half of it solve?
The key (channel id, bucket) — where bucket is a fixed time window. What each half does channel id matches the read pattern. Clients read messages within a chan
Security wants mandatory hardware keys for every login; the business says it will cost conversions. How do you resolve it architecturally rather than by picking a side?
What the interviewer is testing Whether you treat security as a fixed dial to be turned up, or as a risk proportionate design variable. Both stated positions ar
You must roll out MFA to 40,000 employees. Security wants hardware keys; the service desk fears the call volume. Design the rollout.
The framing that resolves the argument Not every identity carries the same risk, so not every identity needs the same factor. A uniform mandate is what creates
A payments API must guarantee that a network retry never charges a customer twice. Design the mechanism end to end.
Why this is unavoidable A client that times out on a POST cannot know whether the request succeeded. Not retrying risks a lost payment; retrying risks a duplica
Partition Keys & Ordering
Ordering guaranteed only within a partition, and choosing the key that makes that enough.
Storage Layout & Partitioning
Partition keys, clustering, and the scan the query planner is left able to skip.
Clocks & Ordering
Why wall clocks lie, and how logical clocks and versions restore order.
Idempotency Keys
Client-generated keys stored atomically with the operation they guard.
AI Gateways
Centralised routing, keys, quotas, caching, logging and safety policy.
CAP & PACELC
What you must give up during a partition, and the latency choice the rest of the time.
Cache Invalidation
Stampedes, penetration, staleness windows and versioned keys.
Competing Consumers
Scaling throughput with instances, at the cost of ordering.
Dead Letter Handling
The poison message that blocks a partition, and the queue nobody reads.
Layered Architecture
The default shape, its clarity, and where a technical partition fails.
Multi-Region Rollout
Ordering regions, bake time, and stopping a bad change before it becomes global.
Pagination & Filtering
Offset versus cursor, stable ordering and unbounded result sets.
Partitioning & Sharding
Splitting data across machines, and the one-way door of a partition key.
Relational Modelling
Normalisation, keys, constraints and the invariants a schema enforces.
Sagas & Compensation
Replacing atomicity with semantic undo, and ordering the irreversible steps last.
Sharding Patterns
Directory versus embedded keys, logical shards and rebalancing.
Webhooks
Push callbacks, signature verification, ordering and at-least-once delivery.