Question: What is the new "Far
Sync" instance in Oracle Data Guard and when would I choose
to use a Far Sync instance over traditional standby
Answer: The far Sync
instance feature is new in Oracle 12c
active Data Guard, an extra-cost feature in Oracle 12c.
Oracle notes that far sync in 12c data guard will enable
zero data loss protection and off-host network compression,
even when primary and standby are thousands of miles apart.
In a nutshell, the Far Sync instance managed the
transport layer of the archived redo logs as they are moved
from the primary to the standby databases. According
to the 12c docs, the Far Sync instance has only three
- Manages a control file
- Receives the redo logs from
the primary database
- Archives the "standby" redo log
files to a local archived redo log filesystem.
The Far Sync instance was created because of the
geographical latency issues when performing synchronous Data
Guard. Essentially, Far Sync is a "proxy" that
physically resides close to the primary database, a
"middleman" instance that manages the near real-time apply
of replication information.
As far as the primary database is concerned, the database
is in-sync, and it is up to the Far Sync instance to ensure
that the data gets transported to the standby database in
near real time.
Data Guard "Near Sync" Standby is in SYNC
mode while "Far sync" Standby ins ASYNC mode.
Notes: See MOSC Note 409013.1