This post is part of a blog series.
Did you know that Oracle Data Guard fast-start failover in maximum performance mode can briefly stall your primary database?
Most users don’t notice, but in environments with strict performance needs, these stalls can matter.
Here’s why: when the database shifts from “UNDER LAG” to “OVER LAG” status, the primary waits for the observer’s acknowledgment. This pause ensures the database doesn’t breach its recovery point objective set with the FastStartFailoverLagLimit property, but it can last up to three seconds (default observer ping time).
Stalls are especially common if the standby can’t keep up with primary redo generation, causing frequent state transitions.
Now in 26ai, the new FastStartFailoverLagGraceTime property lets the observer acknowledge a “pre-stall” before reaching the real lag limit. That way, when the database hits the actual limit, it won’t need to pause: the acknowledge’s already done.
This simple change removes stalls during state transitions, so even the strictest environments meet their performance goals.
What you need to do: set FastStartFailoverLagGraceTime to a value greater than 0 and lower or equal to 3 to make this feature effective. The default of 0 keeps the old behavior.
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