Oracle Database / Data Guard & High Availability
Measure Data Guard transport lag with fresh timestamps
A standby may receive redo late or stop receiving it entirely. Interpret the lag value with the age of its source data.
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, unit, time_computed, datum_time FROM v$dataguard_stats WHERE name = 'transport lag';Read the result
On the standby, DATUM_TIME indicates when source data used for the metric was received. An unchanged timestamp can make a displayed lag misleading.
Resolve and verify
Compare repeated samples with primary redo generation and destination errors. Repair the transport dependency and confirm new redo arrives.
Operational precautions
Do not report zero lag as healthy without checking timestamp freshness and the actual destination.