Far-Sync

Far Sync is an Oracle Data Guard feature that lets you achieve zero data loss (SYNC transport) to a remote standby database without paying the latency penalty on primary transactions. A Far Sync instance sits in a third location between the primary and the standby, receives redo synchronously from the primary (low-latency hop), and then ships it asynchronously to the standby (long-distance hop). 1. Reference Architecture 1.1 Environment Overview Role Hostname DB Unique Name Location OS Primary DB (RAC, 2 nodes) prim01.fra.example.com, prim02.fra.example.com ORCL_FRA Frankfurt DC (AZ-1) OL 8.9 Far Sync Instance farsync01.fra.example.com ORCL_FS Frankfurt DC (AZ-2) OL 8.9 Physical Standby (RAC, 2 nodes) stby01.ams.example.com, stby02.ams.example.com ORCL_AMS Amsterdam DC OL 8.9 DGMGRL / Observer host observer01.fra.example.com — Frankfurt DC (AZ-3) OL 8.9 Oracle version: 19c (19.23 RU) Primary ↔ Far Sync network: Dedicated 10 GbE VLAN, round-trip latency ≈ 0.4 ms Far Sync ↔ Standby network: WAN link, round-trip latency ≈ 8 ms DB_NAME: ORCL (same for all members); DB_UNIQUE_NAME differs per member 2. Live Redo Information Flow The diagram above shows the full geographical redo flow. Below is the step-by-step explanation of how zero data loss is achieved: ...

The redo transport configuration is the most consequential architectural decision in a Data Guard deployment. It determines the data loss exposure (RPO), the performance overhead on the primary, and the recovery point after a failover. Choosing SYNC or ASYNC without understanding the mechanics leads to either unacceptable data loss or unnecessary primary database degradation. Redo Transport Mechanisms ASYNC Transport (ARCN-based) In ASYNC mode, the primary database commits without waiting for the standby to acknowledge receipt of redo. The ARCn background process archives completed log groups and ships them to the standby. ...