Always On Availability Groups (Yüksek Erişilebilirlik Grubu)

Enterprise high-availability and disaster recovery clustering architecture supporting database-level synchronous and asynchronous replica pairs.

Internal Architecture Breakdown

Always On AG operates atop WSFC or Pacemaker quorum frameworks. Synchronous-commit mode guarantees zero data loss (RPO=0) by requiring remote hardening before commit acknowledgment (HADR_SYNC_COMMIT wait), while asynchronous-commit minimizes primary write overhead for DR and read-intent routing.

Node fencing and cluster quorum prevent split-brain dual-primary conditions.

Production Inspection Queries

SQL Server

SELECT r.replica_server_name, d.database_name, s.synchronization_state_desc, s.synchronization_health_desc, s.log_send_queue_size, s.redo_queue_size FROM sys.dm_hadr_database_replica_states s JOIN sys.availability_replicas r ON s.replica_id = r.replica_id JOIN sys.databases d ON s.database_id = d.database_id;

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