This post is part of a blog series.
Often, Data Guard setups use many standby databases, but only some should ever become primary. Others might serve as clone masters, reporting, testing, or staging only.
Previously, you couldn’t prevent an unwanted switchover or failover to these restricted standby databases. This was risky: customers must keep production workloads off test systems.
Oracle Database 26ai introduces a new broker property: PrimaryDatabaseCandidates. Set this to specify which databases can become primary. If you try to switch or fail over to a database not on the list, the broker blocks it.
You can update the candidate list at any time, so it’s flexible in emergencies.
Note: this only blocks broker-initiated switchovers and failovers. Manual SQL conversions bypass this check.
This enhancement has also been back-ported to 19.26.
My colleague Alex Blyth’s blogged about this property in the context of Exascale: https://alexblyth.net/2026/01/12/using-data-guard-broker-to-prevent-a-standby-database-becoming-the-primary/
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