Loading page...
Q&A
Q&ACOUNT(column) excludes NULL values; COUNT(*) counts input rows.
COUNT(*) counts each row in the group regardless of column values. COUNT(column) counts only rows where that expression is non-NULL. When aggregates look low, check nullability and join multiplication before changing the query.
Q&A
Q&ATIME_WAIT is part of safe TCP teardown; verify actual ephemeral-port pressure before tuning sysctls.
TIME_WAIT helps prevent delayed packets from an old connection from contaminating a new one. A high count can be normal. Diagnose port exhaustion by checking outbound tuple reuse, NAT limits, ephemeral port range, and connection pooling. tcp_tw_reuse semantics vary by kernel and are not a universal first fix.
Q&A
Q&ACount repeated statements per request, then batch-load without changing result cardinality.
Trace or log normalized SQL for one request and look for the same child lookup repeated once per parent row. Replace the loop with an eager/batch load or a query at the correct grain. Verify query count and returned rows; a broad join can fix round trips while accidentally multiplying results.
kubernetes
6 minUnderstand eviction admission, readiness accounting, and why a drain can correctly refuse to proceed.
databases
6 minUse a unique ordering tuple and a deliberate visibility policy for reliable page traversal.
kubernetes
8 minLearn how desired state, API objects, and controller loops turn declarative manifests into running workloads.
distributed systems
15 minReason about leader election across partitions and preserve causal context across Kafka, thread pools, and service boundaries.
distributed systems
18 minDesign around Kafka group churn, payment idempotency, coordination limits, sagas, CQRS, and context propagation across async boundaries.