Oracle Database / Data Guard & High Availability
ORA-16855: investigate a transport-lag threshold warning
A transport delay can increase potential data loss exposure. Check whether the standby is receiving fresh redo before changing broker thresholds.
Environment and inputs: Oracle Database 19c baseline · SQL*Plus-compatible SQL unless RMAN, DGMGRL, ADRCI or a host shell is specified. Check release, patch level, edition and container first.
Start with this diagnostic
Use the stated SQL, RMAN, DGMGRL or host shell and replace sample names with approved targets. DBA and V$ views need authorized catalog access in the correct container. Do not grant broad privileges for an example.
SELECT name, value, datum_time FROM v$dataguard_stats WHERE name = 'transport lag';Read the result
The metric needs a current DATUM_TIME and context from primary-side destination errors. A stale value may understate the outage.
Resolve and verify
Correlate network and destination failures with redo generation. Restore the approved transport path and verify new redo arrival and gap resolution.
Operational precautions
Do not declare protection restored merely because the broker warning disappears momentarily.