Ketersediaan tinggi (high availability, HA) bermaksud memastikan pangkalan data tersedia walaupun kegagalan berlaku — melalui replikasi (replica standby), failover automatik (menaik taraf replica apabila primary gagal), dan seni bina yang betul. Matlamatnya: meminimumkan downtime dan kehilangan data, kerana gangguan pangkalan data merobohkan keseluruhan aplikasi.
Asasnya: replikasi + failover automatik
Primary ──(streaming replication)──▶ Standby replica(s)
If the PRIMARY fails:
→ a STANDBY is automatically PROMOTED to become the new primary (FAILOVER)
→ the application reconnects to the new primary → minimal downtime
→ Without HA, a primary failure = total database outage = application down.
