Oracle Data Guard is a brilliant component of Oracle Database Enterprise Edition. On its own, it’s a strong argument in favor of Enterprise Edition. This is because Data Guard is a proven Disaster Recovery solution: it’s integrated, reliable and well known by DBAs. And it comes at no additional cost if you don’t need the Active Guard feature. Several days ago, I helped colleagues of mine troubleshooting a Data Guard configuration: let’s summarize how I would proceed to make my standby database back to sync if I have a problem. In this example, I consider having a simple environment with one primary and one standby in Maximum Availability. If you have multiple standby databases, the tasks are the same.<\/p>\n\n\n\n
The easiest way to check your Data Guard setup is by using the Data Guard CLI called the “broker” from one of the servers. The SHOW CONFIGURATION LAG will display 2 key things: your actual configuration (who is primary, who is standby) and the lag between the databases. The lag should be 0 in most cases:<\/p>\n\n\n\n
. oraenv <<< DBTEST\ndgmgrl \/ \"show configuration lag;\"\n\nDGMGRL for Linux: Release 19.0.0.0.0 - Production on Wed Feb 19 15:06:17 2025\nVersion 19.20.0.0.0\n\nCopyright (c) 1982, 2019, Oracle and\/or its affiliates. All rights reserved.\n\nWelcome to DGMGRL, type \"help\" for information.\nConnected to \"DBTEST_IN\"\nConnected as SYSDG.\n\nConfiguration - dtg\n\n Protection Mode: MaxAvailability\n Members:\n dbtest_in - Primary database\n dbtest_cr - Physical standby database\n Transport Lag: 0 seconds (computed 1 second ago)\n Apply Lag: 0 seconds (computed 1 second ago)\n\nFast-Start Failover: Disabled\n\nConfiguration Status:\nSUCCESS (status updated 26 seconds ago)<\/code><\/pre>\n\n\n\nIf the lag is bigger than a couple of seconds or if you have errors in your configuration, you will need to do some troubleshooting.<\/p>\n\n\n\n
This is an example of a Data Guard configuration not working correctly:<\/p>\n\n\n\n
Configuration - dtg\n\n Protection Mode: MaxAvailability\n Members:\n dbtest_in - Primary database\n Error: ORA-16810: multiple errors or warnings detected for the member\n\n dbtest_cr - Physical standby database\n Warning: ORA-16854: apply lag could not be determined\n\nFast-Start Failover: Disabled\n\nConfiguration Status:\nERROR (status updated 56 seconds ago)<\/code><\/pre>\n\n\n\nCheck the Fast Recovery Area on your standby database<\/h2>\n\n\n\n
A common problem you may have on a standby database is the Fast Recovery Area (FRA) being full. You probably know that a standby database will apply the changes from the primary without waiting for the archivelog to be shipped, but the archivelog is shipped anyway to the standby. This is because there is no guarantee that the standby database is always up and running, so archivelogs must be transported to the other site for later apply if needed. Another thing is that you probably enabled Flashback Database on both databases, and archivelogs are required for a Flashback Database operation. These shipped archivelogs will naturally land in the FRA, and unless you configured a deletion policy, they will never be deleted. As you probably don’t do backups on the standby database, nothing could flag these archivelogs as reclaimable (meaning that they are now useless and can be deleted). If your FRA is quite big, you may discover this problem several weeks or months after the initial setup.<\/p>\n\n\n\n
Check the FRA usage on your standby with this query:<\/p>\n\n\n\n
select sum(PERCENT_SPACE_USED-PERCENT_SPACE_RECLAIMABLE) \"Real FRA usage %\" from v$flash_recovery_area_usage;\nReal FRA usage %\n----------------\n 32.86<\/code><\/pre>\n\n\n\nIf the FRA is almost full, you can remove older archivelogs, for example those older than 2 days if your standby has a 1-day lag:<\/p>\n\n\n\n
rman target \/\ndelete force noprompt archivelog all completed before 'sysdate-2';\nexit;\n<\/code><\/pre>\n\n\n\nThen check again the FRA and the lag of your Data Guard setup.<\/p>\n\n\n\n
Check standby_file_management parameter<\/h2>\n\n\n\n
Another thing that can break your sync is the standby_file_management parameter having an incorrect value. In most cases, it must be set to AUTOMATIC: it means that any file created on the primary will be created on the standby. It’s the way it is supposed to work:<\/p>\n\n\n\n
show parameter standby_file_management\nNAME\t\t\t\t TYPE\t VALUE\n------------------------------------ ----------- ------------------------------\nstandby_file_management \t string\t AUTO<\/code><\/pre>\n\n\n\nIf standby_file_management is set to MANUAL, your standby will not be in sync anymore as soon as a new datafile is created on the primary. You will need to manually create the file on the standby to continue the sync. Not very convenient.<\/p>\n\n\n\n
The MANUAL mode exists because some older configurations had different filesystems on primary and on standby and didn’t use OMF, meaning that standby database cannot guess where to put the new file.<\/p>\n\n\n\n
Both primary and standby databases must have this parameter set to AUTO nowadays.<\/p>\n\n\n\n
Cross test connexions<\/h2>\n\n\n\n
Your Data Guard setup can only work if your databases are able to communicate together. If you are not so sure if something changed on your network, for example a new firewall rule, check your connexions from both servers using the SYS account.<\/p>\n\n\n\n
From your primary:<\/p>\n\n\n\n
sqlplus sys@DBTEST_CR as sysdba\nsqlplus sys@DBTEST_IN as sysdba\n<\/code><\/pre>\n\n\n\nFrom your standby:<\/p>\n\n\n\n
sqlplus sys@DBTEST_CR as sysdba\nsqlplus sys@DBTEST_IN as sysdba<\/code><\/pre>\n\n\n\nCheck password file<\/h2>\n\n\n\n
When your standby database is MOUNTED, the only way to authenticate the SYS user is by using the password file. If you changed the SYS password on the primary, it will be changed inside the database (and replicated) as well as in the local password file, but the password file on the standby site won’t be updated. You must then copy the password file from the primary database to the standby database. Copy is done with a scp command, for example from my primary server:<\/p>\n\n\n\n
\nsrvctl config database -db DBTEST_IN | grep Password\nPassword file: \/u01\/app\/odaorahome\/oracle\/product\/19.0.0.0\/dbhome_4\/dbs\/orapwDBTEST\n\nscp `srvctl config database -db OP1 | grep Password | awk '{print $3;}'` oracle@oda-x11-cr:`srvctl config database -db OP1 | grep Password | awk '{print $3;}'`<\/code><\/pre>\n\n\n\nA restart of the standby database may be needed.<\/p>\n\n\n\n
Check alert_DBTEST.log and drcDBTEST.log on both servers<\/h2>\n\n\n\n
Never miss an error reported in the alert_DBTEST.log on both sides. I would recommend disabling the Data Guard configuration, doing a tail -f on both alert_DBTEST.log files, and enabling back the configuration:<\/p>\n\n\n\n
. oraenv <<< DBTEST\ndgmgrl \/ \"disable configuration;\"\nsleep 60\ndgmgrl \/ \"enable configuration;\"<\/code><\/pre>\n\n\n\nThere are also dedicated trace files for Data Guard, at the same place as alert_DBTEST.log: drcDBTEST.log. You may find additional information for troubleshooting your configuration in these files.<\/p>\n\n\n\n
Remove and recreate the configuration<\/h2>\n\n\n\n
Data Guard configuration is just a couple of parameters stored in a file on both sides. It’s easy to drop and create again this configuration without actually rebuilding the standby database. If you want to make sure that nothing survives from your old configuration, just remove the broker files before creating the configuration again.<\/p>\n\n\n\n
From the primary:<\/p>\n\n\n\n
dgmgrl sys\nedit configuration set protection mode as maxperformance;\nremove configuration;\nexit;\n\nsqlplus \/ as sysdba\nsho parameter dg_broker_config_file\n\nNAME\t\t\t\t TYPE\t VALUE\n------------------------------------ ----------- ------------------------------\ndg_broker_config_file1\t\t string\t \/u01\/app\/odaorahome\/oracle\/pro\n\t\t\t\t\t\t duct\/19.0.0.0\/dbhome_4\/dbs\/dr1\n\t\t\t\t\t\t DBTEST_IN.dat\ndg_broker_config_file2\t\t string\t \/u01\/app\/odaorahome\/oracle\/pro\n\t\t\t\t\t\t duct\/19.0.0.0\/dbhome_4\/dbs\/dr2\n\t\t\t\t\t\t DBTEST_IN.dat\nalter system set dg_broker_start=FALSE;\n\nhost rm \/u01\/app\/odaorahome\/oracle\/product\/19.0.0.0\/dbhome_4\/dbs\/dr1DBTEST_IN.dat\nhost rm \/u01\/app\/odaorahome\/oracle\/product\/19.0.0.0\/dbhome_4\/dbs\/dr2DBTEST_IN.dat\n\nexit\n<\/code><\/pre>\n\n\n\nFrom the standby:<\/p>\n\n\n\n
sqlplus \/ as sysdba\nsho parameter dg_broker_config_file\n\nNAME\t\t\t\t TYPE\t VALUE\n------------------------------------ ----------- ------------------------------\ndg_broker_config_file1\t\t string\t \/u01\/app\/odaorahome\/oracle\/pro\n\t\t\t\t\t\t duct\/19.0.0.0\/dbhome_4\/dbs\/dr1\n\t\t\t\t\t\t DBTEST_CR.dat\ndg_broker_config_file2\t\t string\t \/u01\/app\/odaorahome\/oracle\/pro\n\t\t\t\t\t\t duct\/19.0.0.0\/dbhome_4\/dbs\/dr2\n\t\t\t\t\t\t DBTEST_CR.dat\nalter system set dg_broker_start=FALSE;\n\nhost rm \/u01\/app\/odaorahome\/oracle\/product\/19.0.0.0\/dbhome_4\/dbs\/dr1DBTEST_CR.dat\nhost rm \/u01\/app\/odaorahome\/oracle\/product\/19.0.0.0\/dbhome_4\/dbs\/dr2DBTEST_CR.dat\n\nalter system set dg_broker_start=TRUE;\nexit\n<\/code><\/pre>\n\n\n\nFrom the primary:<\/p>\n\n\n\n
sqlplus \/ as sysdba\nalter system set dg_broker_start=TRUE;\nexit;\n\ndgmgrl sys\ncreate configuration DTG as primary database is 'DBTEST_IN' connect identifier is 'DBTEST_IN';\nadd database 'DBTEST_CR' as connect identifier is 'DBTEST_CR';\nenable configuration;\nedit database 'DBTEST_CR' set property LogXptMode='SYNC';\nedit database 'DBTEST_IN' set property LogXptMode='SYNC';\nedit database 'DBTEST_CR' set property StandbyFileManagement='AUTO';\nedit database 'DBTEST_IN' set property StandbyFileManagement='AUTO';\nEDIT DATABASE 'DBTEST_CR' SET PROPERTY 'ArchiveLagTarget'=1200;\nEDIT DATABASE 'DBTEST_IN' SET PROPERTY 'ArchiveLagTarget'=1200;\nEdit database 'DBTEST_CR' set property StaticConnectIdentifier='(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=oda-x11-cr)(PORT=1521))(CONNECT_DATA=(SERVICE_NAME=DBTEST_CR)(INSTANCE_NAME=DBTEST)(SERVER=DEDICATED)))';\nEdit database 'DBTEST_IN' set property StaticConnectIdentifier='(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=oda-x11-in)(PORT=1521))(CONNECT_DATA=(SERVICE_NAME=DBTEST_IN)(INSTANCE_NAME=DBTEST)(SERVER=DEDICATED)))';\nedit configuration set protection mode as maxavailability;\nshow configuration lag;\nexit;<\/code><\/pre>\n\n\n\nNote that the StaticConnectIdentifier property is only mandatory when using a port different than 1521.<\/p>\n\n\n\n
Recover standby database from service<\/h2>\n\n\n\n
If you still struggle to get your standby back in sync, because too many archivelogs are missing or because the archivelogs are not on the primary site anymore, you can use this nice RMAN command on your standby:<\/p>\n\n\n\n
sqlplus \/ as sysdba\nalter system set dg_broker_start=false;\nexit;\n\nsrvctl stop database -db DBTEST_CR\nsleep 10\nsrvctl start database -db DBTEST_CR -o mount\n\nrman target \/\nrecover database from service 'DBTEST_IN';\nexit;\n\nsqlplus \/ as sysdba\nalter system set dg_broker_start=true;\nexit;\n<\/code><\/pre>\n\n\n\nThis RECOVER DATABASE FROM SERVICE will do an incremental backup on the primary to recover the standby without needing the missing archivelogs. It’s convenient and much faster than rebuilding the standby from scratch.<\/p>\n\n\n\n
Check SCN<\/h2>\n\n\n\n
In the good old days of Data Guard on Oracle 9i, the broker didn’t exist and you had to configure everything yourself. At this time, I used to have a look at the SCN on both databases for monitoring the lag. Nothing changed regarding the SCN: on a primary, you will never see the same SCN each time you query its value. This is because the query itself will increase the SCN by 1, as well as other background queries are running:<\/p>\n\n\n\n
select current_scn from v$database;\nCURRENT_SCN\n-----------\n 271650667\n\nselect current_scn from v$database;\nCURRENT_SCN\n-----------\n 271650674\n\nselect current_scn from v$database;\nCURRENT_SCN\n-----------\n 271650675\n\nselect current_scn from v$database;\nCURRENT_SCN\n-----------\n 271650678<\/code><\/pre>\n\n\n\nOn a standby database, the SCN can only increase if changes are pushed by a primary. And for sure, the SCN will always be lower than the one on the primary. If your standby database is not opened, meaning that you don’t have the Active Guard option, you will query the same SCN for a couple of minutes, and you will see big jumps in figures from time to time:<\/p>\n\n\n\n
select current_scn from v$database;\nCURRENT_SCN\n-----------\n 271650664\n\nselect current_scn from v$database;\nCURRENT_SCN\n-----------\n 271650664\n\nselect current_scn from v$database;\nCURRENT_SCN\n-----------\n 271651042\n\nselect current_scn from v$database;\nCURRENT_SCN\n-----------\n 271651042<\/code><\/pre>\n\n\n\nConclusion<\/h2>\n\n\n\n
With these few tips, troubleshooting Data Guard might be easier now.<\/p>\n\n\n\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
Troubleshooting Oracle Data Guard when your standby database has errors or is not in sync<\/p>\n","protected":false},"author":45,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[59],"tags":[60,958,63,3560,3558,3555,3561,3556,3562,2043,3552,3550,3551,236,2203],"type_dbi":[],"class_list":["post-37414","post","type-post","status-publish","format-standard","hentry","category-oracle","tag-12c","tag-12cr2","tag-21c","tag-23ai","tag-apply-lag","tag-data-guard-error","tag-data-guard-problem","tag-dataguard-error","tag-dataguard-problem","tag-dgmgrl","tag-lag","tag-ora-16810","tag-ora-16854","tag-oracle-data-guard","tag-oracle-database"],"acf":[],"yoast_head":"\n
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