01
junior⏱ 20 min
Missing Index on High-Traffic Table
Simple SELECT query taking 12 seconds instead of 50ms after data growth.
PostgreSQLEXPLAINIndexes
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Database Performance
From slow queries to connection pooling
📚 5 cases⏱ 6 hoursJunior → Senior1 Junior3 Middle1 Senior
Cases in this track
02
middle⏱ 22 min
Redis Memory Eviction Killing Cache Hit Rate
Cache hit rate dropped from 94% to 31% overnight. DB hammered.
RedisCacheEviction Policy
03
middle⏱ 25 min
PostgreSQL Connection Pool Exhaustion
Response time degraded from 150ms to 8000ms. Error rate jumped to 22%.
PostgreSQLHikariCPJava
04
senior⏱ 40 min
Transaction Deadlock Under High Concurrency
Sporadic 500 errors during peak load. Deadlock detected in pg_locks.
PostgreSQLTransactionsLocks
05
middle⏱ 30 min
Streaming Replication Lag Causing Stale Reads
Read replica 45 seconds behind primary. Stale data served to users.
PostgreSQLReplicationWAL