Linking an Oracle physical standby database

This topic describes special considerations for linking Oracle physical standby databases.

The Delphix Engine supports linking both physical and logical standby databases. In previous versions of the Delphix Engine, limitations were placed upon support for Oracle RAC physical standby databases in Real-Time Apply mode. In version 3.0 of the Delphix Engine, these restrictions were lifted.

Using block change tracking (BCT) on a physical standby database

In general, Delphix recommends enabling Block Change Tracking (BCT) on a primary or standby source database. See the Physical Standby Database Support Matrix below for restrictions on enabling BCT on a standby database.

BCT is available from Oracle release 11.1.0.6 onward for physical standby databases only if they are licensed for the Active Data Guard option.

Release 11.1.0.6 is unstable for the BCT on physical standby feature
Release 11.1.0.7 requires a patch for Oracle bugs 7613481, 9068088
Release 11.2.0.2 requires patches for Oracle bugs 10170431, 12312133
Release 11.2.0.3 requires patches for Oracle bugs 12312133, 16052165

Patches required

Enabling BCT on a physical standby database without these patches is not recommended because of serious performance and stability issues.

BCT on a primary database has been stable since Oracle version 10.2.0.5. In order to make use of BCT (>11.2.0.4), The Physical Standby Database must be in a "Managed Recovery Mode", i.e. achieved using "ALTER DATABASE RECOVER MANAGED STANDBY DATABASE".

Physical standby database support matrix

Oracle Version	Apply Mode	Notes
11.x and 12.x in LevelBackup mode; 12.x in SCN Backup mode	Archive Apply mode	No special restrictions.
	Real-Time Apply mode (RTA)	LogSync must be enabled for all database versions if RTA is enabled
11.x in SCN Backup mode	Archive Apply mode	If the Physical Standby Database is at version 11.2.0.4 or above, no special actions are required. Due to Oracle bug 10146187, Redo Apply must be stopped and the database opened in read-only mode during SnapSync. See the section Stopping and Restarting Redo Apply below for more information.
	Real-Time Apply mode	If the Physical Physical Standby Database is at version 11.2.0.4 or above, no special actions are required. LogSync must be enabled. Due to Oracle bug 10146187, Redo Apply must be stopped and the database opened in read-only mode during SnapSync. See the section Stopping and Restarting Redo Apply below for more information. In addition, to avoid Oracle Bug 13075226, which results in a hang during the restart of Redo Apply, Delphix requires disabling using BCT on the standby database. The hang occurs when BCT is enabled on a standby database that uses SCN backup mode. Patch required SnapSync will fail If running Oracle 11.2 before 11.2.0.4 when using SCN backups and real-time apply mode, Use level based backups instead. If the Oracle installation has already been patched for Oracle bug 13075226, or once the patch is applied, use the CLI to update the repository for this installation so that applied Patches include Oracle bug number 13075226. If the repository does not indicate that Oracle bug 13075226 for the repository has been addressed, SnapSync will not be possible when using SCN backups and real-time apply. See Updating Repository for Oracle applied patches with the Command Line Interface below for details on how to update the repository.
18.0.0.0 - 19.3.0.0	Real-Time Apply mode	Oracle patch 29056767 installed, Failure to install this patch may result in SnapSync failure with error.

Level backup mode for SnapSync

By default, the Delphix Engine's SnapSync feature uses SCN Backup mode and is designed to not interfere with other backups that may already be in use. However, in cases where RMAN is not being used outside of the Delphix Engine, the Delphix Engine can use the Level Backup mode that improves SnapSync behavior on Oracle 11g physical standby databases. In this mode, redo apply does not have to be stopped during SnapSync. See Advanced Data Management Settings for Oracle dSources for more information about SnapSync settings.

Requirements for using level backup mode

Customer not backing up their physical standby with RMAN:

Set CONTROL_FILE_RECORD_KEEP_TIME to 365

OR all of the following:

Physical standby database running Oracle 11.2.0.2 or later version
All RMAN backups must use tags
RMAN CROSSCHECK commands must specify tags
RMAN DELETE commands must specify tags
RMAN DUPLICATE commands must specify tags
Set CONTROL_FILE_RECORD_KEEP_TIME to 365

Failure to meet all of these requirements will cause external RMAN backups to be incomplete or result in corrupt SnapSync snapshots. Switching from SCN to LEVEL mode will force a new LEVEL 0 backup.

Stopping and restarting redo apply

Oracle bug 10146187 requires stopping of redo apply before an SCN-based incremental backup can be issued. These scripts can be used as pre- and post-scripts during the dSource linking process to stop and restart Redo Apply.

SnapSync pre-script: disableStandby.sh.template
SnapSync post-script: enableStandby.sh.template

These scripts must be modified for local use, particularly regarding whether the physical standby database operates in MOUNTED or OPEN mode.

These scripts are only required if your Physical Standby database is on a version of Oracle 11g that does not have the fix for Oracle bug 10146187 (consult Oracle documentation for details).

Failure to properly customize these scripts could violate your Oracle license terms by running redo apply on an open database, which requires an Oracle Active Data Guard license.

Linking and provisioning a Mounted Standby

When you link a standby database in the mounted mode and have not been opened read-only, the data files for temporary tablespaces will be present in v$tempfile but will not actually be created yet, and therefore will indicate 0 file size. As a result, any VDB provisioned from a snapshot taken in this state will end up with the same tablespaces and datafiles created, but with a default file size of 52428800 bytes.

For databases that are in the mounted state, the Delphix database user account must be SYS (having the SYSDBA role), SYSBACKUP (having the SYSBACKUP role) or SYSDG (having the SYSDG role).

SYSBACKUPand SYSDG roles are only available in Oracle 12.1 and later releases.

However, for an open standby (Active Data Guard) database, only a regular database user account is required.

Connecting to a mounted standby with a SYS user account requires that the mounted standby be configured with a password file. Delphix does not capture the password file during SnapSync, and for this reason, cannot provision or sync validate a database with a SYS user. A secondary, regular database user account can be specified through either the Delphix Management application or CLI. This database user will then be used to connect to the database during provisioning and validated sync. Note that the SYS user is still required to perform snapshots of the source database.

In the Delphix Management application, the non-SYS user can be specified from within the Add dSource wizard, or on the back of the Oracle dSource after linking.