When deploying Oracle GoldenGate for large-scale replication, one of the most critical decisions is: Where should we run the initial load and CDC (Change Data Capture)? This decision affects performance, supportability, and operational risk, especially when working with Active Data Guard (ADG), snapshot standby, or Primary/cloned databases.
This blog post breaks down the supported configurations, highlights Oracle’s certification boundaries, and presents a proven approach validated in production environments.
Understanding Initial Load vs. CDC
- Initial Load: A one-time bulk copy of source tables to the target using GoldenGate Extract (SOURCEISTABLE) and Replicat (SPECIALRUN).
- CDC (Change Data Capture): Continuous replication of changes using Extract (TRANLOG) and Replicat (INTEGRATED or NONINTEGRATED), typically mining redo logs.
Each mode has different requirements,especially around database role and read/write access.
Deep Dive: ADG Standby
Oracle GoldenGate does support CDC from ADG standby using Classic Extract with TRANLOGOPTIONS MINEFROMACTIVEDG. However, initial load is not supported from ADG because it is read-only.
“Initial load Extracts must connect to the primary database because Active Data Guard is read-only. For CDC, Extract is registered on the primary but can mine redo from ADG standby using TRANLOGOPTIONS MINEFROMACTIVEDG.”
Additionally, Integrated Extract is not supported on ADG:
“It is not possible to configure Integrated Extract to mine from ADG. For using Integrated Extract, the database must be in open mode as it makes changes to internal system tables to capture its metadata.” — Oracle Support Doc ID 2343707.1
Snapshot Standby: Why It’s Risky
Snapshot standby databases are temporarily opened in read-write mode, which makes initial load technically possible. However, Oracle does not certify this configuration. The problem arises when converting back to physical standby to resume redo apply, this interrupts redo transport and breaks CDC consistency.
Extract cannot reliably mine redo during or after these transitions. Snapshot standby → Technically possible for table reads, but not supported due to role conversion issues
Recommended Approach: Primary Database or Clone Database (Read-Write)
The most reliable and supported method is to create a dedicated clone database from either the primary or ADG standby, and open it in read-write mode.
Initial Load: Run Extract (SOURCEISTABLE) and Replicat (SPECIALRUN) from the clone.
CDC: Register Extract on the source database (primary), then capture changes continuously. Replicat applies changes in real time.
Summary
When planning Oracle GoldenGate deployments, choosing the right source database for initial load and CDC is critical. Initial load Extracts require a read-write connection, making Active Data Guard (ADG) standby unsuitable due to its read-only nature. Snapshot standby may allow table reads temporarily, but it’s not Oracle-certified and poses risks during role transitions. The most reliable and supported approach is to use a dedicated clone database opened in read-write mode for the initial load, followed by CDC configured from the source database where Extract is properly registered. This method has been tested in production environments and ensures a smooth, supported, and high-performance replication strategy.
