Replikering vedligeholder kopier af data på tværs af flere servere — for tilgængelighed (overlevelse af fejl), læseskalering (betjening af læsninger fra kopier) og geografisk distribution. Forskellige strategier (primary-replica, multi-primary, sync vs async) involverer kompromiser.
Hvorfor replikeres
✓ AVAILABILITY/redundancy → if one copy fails, others have the data (no data loss, failover)
✓ READ SCALING → serve reads from replicas (offload the primary) → handle more reads
✓ GEO-DISTRIBUTION → copies near users (lower latency); disaster recovery
→ replication is fundamental to reliable, scalable data systems.
