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Coding Challenges
5,893 curated questions across every arena — browse by topic, then jump into a live 2-minute battle to put them to the test.
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4,318 challenges matching your filters
- Multiple ChoiceHard
LSM tree read amplification tradeoff
lsm-treestorage-engineread-amplification - Multiple ChoiceBeginner
WAL durability on crash
waldurabilitycrash-recovery - Multiple ChoiceHard
Write skew under snapshot isolation
mvccwrite-skewisolation-levels - Multiple ChoiceIntermediate
Quorum read-write overlap formula
quorumreplicationconsistency - Multiple ChoiceBeginner
Read-your-writes routing
replication-lagread-your-writesconsistency - Multiple ChoiceHard
Raft safety vs Paxos roles
raftpaxosconsensus - Multiple ChoiceBeginner
Kafka partition ordering guarantee
kafkapartitioningordering - Multiple ChoiceIntermediate
Exactly-once via idempotent producer
kafkaexactly-oncetransactions - Multiple ChoiceBeginner
SQS visibility timeout semantics
sqsvisibility-timeoutat-least-once - Multiple ChoiceHard
Sliding window counter hybrid tradeoff
rate-limitingsliding-windowalgorithms - Multiple ChoiceHard
Distributed rate limiting consistency
rate-limitingdistributedconsistency - Multiple ChoiceIntermediate
GraphQL resolver N+1
graphqln+1batching - Multiple ChoiceBeginner
Keyset pagination on a busy table
paginationcursorperformance - Multiple ChoiceHard
Fencing tokens for stale leaders
fencing-tokenssplit-brainleader-election - Multiple ChoiceBeginner
Snowflake ID clock rollback
snowflakeclock-skewunique-id - Multiple ChoiceIntermediate
Error budget burn policy
sloerror-budgetreliability - Multiple ChoiceBeginner
Circuit breaker half-open state
circuit-breakerresiliencefault-tolerance - Multiple ChoiceBeginner
Retry backoff with jitter
retrybackoffjitter - Multiple ChoiceIntermediate
Tail sampling versus head sampling
tracingtail-samplingobservability - Multiple ChoiceBeginner
S3 strong read-after-write consistency
s3consistencyobject-storage - Multiple ChoiceHard
Redlock safety criticism
distributed-locksredlockclock-skew - Multiple ChoiceBeginner
Multi-region active-active vs active-passive
multi-regionavailabilitytopology - Multiple ChoiceIntermediate
Data residency constraint enforcement
gdprdata-residencycompliance - Multiple ChoiceBeginner
Cross-region quorum latency cost
quorumlatencymulti-region - Multiple ChoiceHard
OR-Set vs LWW register semantics
crdtor-setconflict-resolution - Multiple ChoiceBeginner
Hybrid logical clock purpose
hlcclockscausality - Multiple ChoiceBeginner
Bloom filter false negative property
bloom-filterprobabilisticmembership - Multiple ChoiceHard
Cuckoo filter vs bloom filter trade-off
cuckoo-filterbloom-filterdeletion - Multiple ChoiceBeginner
HyperLogLog cardinality error
hyperloglogcardinalityapproximation - Multiple ChoiceHard
t-digest for streaming percentiles
t-digestpercentilesstreaming - Multiple ChoiceBeginner
Skip list expected complexity
skip-listdata-structurescomplexity - Multiple ChoiceIntermediate
Size-tiered vs leveled compaction
lsmcompactionwrite-amplification - Multiple ChoiceHard
Tombstone accumulation in LSM
tombstoneslsmcompaction - Multiple ChoiceIntermediate
B+tree vs LSM read/write trade-off
btreelsmtrade-offs - Multiple ChoiceBeginner
Postgres autovacuum bloat cause
postgresvacuumbloat - Multiple ChoiceHard
HOT updates and indexed columns
postgreshot-updatesindexes - Multiple ChoiceIntermediate
Connection pool sizing math
connection-poolsizingcapacity - Multiple ChoiceHard
PgBouncer transaction vs session pooling
pgbouncerconnection-poolpostgres - Multiple ChoiceBeginner
Read replica routing lag hazard
read-replicasreplication-lagconsistency - Multiple ChoiceBeginner
Hash sharding hotspot risk
shardinghashinghotspots - Multiple ChoiceHard
Dual-write migration correctness
migrationdual-writeconsistency - Multiple ChoiceBeginner
Full jitter retry rationale
backoffjitterretries - Multiple ChoiceBeginner
Token bucket burst cap
token-bucketrate-limitingburst - Multiple ChoiceIntermediate
Preventing seat oversell
concurrencybookingoversell - Multiple ChoiceHard
Saga compensation ordering
sagacompensationorchestration - Multiple ChoiceBeginner
Double-Entry Ledger Balance Invariant
ledgerdouble-entryinvariants - Multiple ChoiceBeginner
Purpose of Idempotency Keys in Payments
paymentsidempotencyretries - Multiple ChoiceBeginner
Append-Only Event Store for Finance
event-storefinanceaudit - Multiple ChoiceBeginner
Why Reconciliation Jobs Exist
reconciliationsettlementledger - Multiple ChoiceBeginner
Exactly-Once vs At-Least-Once Semantics
exactly-onceidempotencymessaging - Multiple ChoiceBeginner
Per-User Quiet Hours in Notifications
notificationsquiet-hourstimezone - Multiple ChoiceHard
Ledger Immutability and Corrections
ledgerimmutabilitycorrections - Multiple ChoiceIntermediate
Saga Choreography vs Orchestration Tradeoff
sagaorchestrationchoreography - Multiple ChoiceBeginner
Audit Trail Tamper Evidence
audittamper-evidenthash-chain - Multiple ChoiceBeginner
Push vs Pull Notification Delivery
notificationspushpull - Multiple ChoiceBeginner
CRDT vs OT for Collaboration
collaborationcrdtot - Multiple ChoiceHard
Adaptive Bitrate Ladder Design
videoabrhls - Multiple ChoiceHard
Sharded Timers for Job Scheduler
schedulershardingtimers - Multiple ChoiceIntermediate
Fan-Out on Write vs Read
news-feedfan-outcelebrity - Multiple ChoiceIntermediate
Stable Cursor Pagination
paginationfeedcursor
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