.jpg "Click to see the Ultimate Data Guard Health Check Script")
If you are a DBA, you know the panic of a "Quiet Standby." The alerts are silent. The phone isn't ringing. But deep down, you wonder: Is my Disaster Recovery (DR) site actually in sync, or has it been stuck on Sequence #10452 since last Tuesday?
Too many monitoring tools (like OEM or Zabbix) only trigger an alert when the lag hits a threshold (e.g., "Lag > 30 Mins"). By then, it’s often too late. You don't just want to know if there is a lag; you need to know where the lag is.
Is it the Network (Transport Lag)? Or is it the Disk/CPU (Apply Lag)?
Below is the exact script I use in my daily health checks. It consolidates 4 different dynamic performance views (v$dataguard_stats, v$managed_standby, v$archive_gap, v$database) into one single "Truth" report.
The Script (dg_health_check.sql)
Save this as dg_health_check.sql and run it on your Standby Database.
SET LINESIZE 200 PAGESIZE 1000 CHECK OFF FEEDBACK OFF ECHO OFF VERIFY OFF
COL name FORMAT a30
COL value FORMAT a20
COL unit FORMAT a30
COL time_computed FORMAT a25
COL process FORMAT a10
COL status FORMAT a15
COL sequence# FORMAT 99999999
COL block# FORMAT 999999
COL error_message FORMAT a50
PROMPT ========================================================
PROMPT ORACLE DATA GUARD HEALTH CHECK (Run on Standby)
PROMPT ========================================================
PROMPT
PROMPT 1. DATABASE ROLE & PROTECTION MODE
PROMPT ----------------------------------------
SELECT name, db_unique_name, database_role, open_mode, protection_mode
FROM v$database;
PROMPT
PROMPT 2. REAL-TIME LAG STATISTICS (The Source of Truth)
PROMPT ----------------------------------------
-- Transport Lag = Delay in receiving data (Network Issue)
-- Apply Lag = Delay in writing data (IO/CPU Issue)
SELECT name, value, unit, time_computed
FROM v$dataguard_stats
WHERE name IN ('transport lag', 'apply lag', 'estimated startup time');
PROMPT
PROMPT 3. MRP (MANAGED RECOVERY PROCESS) STATUS
PROMPT ----------------------------------------
-- IF NO ROWS SELECTED: Your recovery is STOPPED.
-- Look for 'APPLYING_LOG' or 'WAIT_FOR_LOG'
SELECT process, status, thread#, sequence#, block#
FROM v$managed_standby
WHERE process LIKE 'MRP%';
PROMPT
PROMPT 4. GAP DETECTION
PROMPT ----------------------------------------
-- If rows appear here, you have a missing archive log that FAL_SERVER could not fetch.
SELECT * FROM v$archive_gap;
PROMPT
PROMPT 5. RECENT ERRORS (Last 10 Events)
PROMPT ----------------------------------------
SELECT TO_CHAR(timestamp, 'DD-MON-RR HH24:MI:SS') as err_time, message
FROM v$dataguard_status
WHERE severity IN ('Error','Fatal')
AND timestamp > sysdate-1
ORDER BY timestamp DESC
FETCH FIRST 10 ROWS ONLY;
PROMPT ========================================================
PROMPT END OF REPORT
PROMPT ========================================================
How to Analyze the Output (Like a Senior DBA)
Scenario A: High Transport Lag
What you see:
Transport Lagis high (e.g.,+00 01:20:00), butApply Lagis low.What it means: Your Primary database is generating Redo faster than your network can ship it.
The Fix: Check your network bandwidth. If you are using Oracle 19c or 23ai, consider enabling Redo Compression in your Data Guard broker configuration (
EditDatabase Set Property RedoCompression='ENABLE').
Scenario B: High Apply Lag
What you see:
Transport Lagis near 0, butApply Lagis climbing (e.g.,+00 00:45:00).What it means: The data is there (on the standby server), but the database can't write it to disk fast enough. This often happens during batch loads or index rebuilds on the Primary.
The Fix: Check I/O stats on the Standby. Ensure you are using Real-Time Apply so the MRP (Managed Recovery Process) reads directly from Standby Redo Logs (SRLs) rather than waiting for archive logs to be finalized.
Scenario C: MRP Status is "WAIT_FOR_GAP"
What you see: In Section 3, the status is
WAIT_FOR_GAP.What it means: A severe gap has occurred. The Standby is missing a specific sequence number and cannot proceed until you manually register that file.
The Fix: Run the query in Section 4 (
v$archive_gap) to identify the missing sequence, restore it from backup, and register it.
Why this works in 2026
Old school scripts relied on v$archived_log, which only tells you history. In modern Oracle Cloud (OCI) and Hybrid environments, v$dataguard_stats is the only view that accurately calculates the time difference between the Primary commit and the Standby visibility.
Chetan Yadav is a Senior Oracle, PostgreSQL, MySQL & Cloud DBA with 14+ years of experience supporting high-traffic production environments across AWS, Azure, and on-premise systems. His core expertise includes Oracle RAC, ASM, Data Guard, performance tuning, HA/DR design, monitoring frameworks, and real-world troubleshooting.
He also trains DBAs globally through deep-dive technical content, hands-on sessions, and automation workflows using n8n, AI tools, and modern monitoring stacks. His mission is to help DBAs solve real production problems and grow into high-paying remote roles worldwide.
Chetan regularly publishes expert content across Oracle, PostgreSQL, MySQL, and Cloud DBA technologies—including performance tuning guides, DR architectures, monitoring tools, scripts, and real incident-based case studies.
Explore More Technical Work
LinkedIn (Professional Profile & Articles)
https://www.linkedin.com/in/chetanyadavvds/
YouTube – Oracle Foundations Playlist
https://www.youtube.com/playlist?list=PL5TN6ECUWGROHQGXep_5hff-2ageWTp4b
Telegram – LevelUp_Careers DBA Tips
https://t.me/LevelUp_Careers
Instagram – Oracle/Cloud Learning Reels
https://www.instagram.com/levelup_careers/
Facebook Page – OracleDBAInfo
https://www.facebook.com/OracleDBAInfo
These platforms feature guides, scripts, diagrams, troubleshooting workflows, and real-world DBA case studies designed for database professionals worldwide.
