What’s New in Oracle Data Guard 10g Release 2?
This capability allows Data Guard to automatically, and quickly fail over to a previously chosen, synchronized standby database in the event of loss of the primary database, without requiring any manual steps to invoke the failover, and without incurring any data loss. Following a fast-start failover, once the old primary database is repaired, Data Guard automatically reinstates it to be a standby database. This act restores high availability to the Data Guard configuration.
Improved Redo Transmission
Several enhancements have been made in the redo transmission architecture to make sure redo data generated on the primary database can be transmitted as quickly and efficiently as possible to the standby database(s).
Easy conversion of a physical standby database to a reporting database
A physical standby database can be activated as a primary database, opened read/write for reporting purposes, and then flashed back to a point in the past to be easily converted back to a physical standby database. At this point, Data Guard automatically synchronizes the standby database with the primary database. This allows the physical standby database to be utilized for read/write reporting and cloning activities.
Automatic deletion of applied archived redo log files in logical standby databases
Archived logs, once they are applied on the logical standby database, are automatically deleted, reducing storage consumption on the logical standby and improving Data Guard manageability. Physical standby databases have already had this functionality since Oracle Database 10g Release 1, with Flash Recovery Area.
Fine-grained monitoring of Data Guard configurations
Oracle Enterprise Manager has been enhanced to provide granular, up-to-date monitoring of Data Guard configurations, so that administrators may make an informed and expedient decision regarding managing this configuration.
Real Time Apply:
With this feature, redo data can be applied on the standby database (whether Redo Apply or SQL Apply) as soon as they have written to a Standby Redo Log (SRL). Prior releases of Data Guard require this redo data to be archived at the standby database in the form of archivelogs before they can be applied. The Real Time Apply feature allows standby databases to be closely synchronized with the primary database, enabling up-to-date and real-time reporting (especially for Data Guard SQL Apply). This also enables faster switchover and failover times,whichinturn reduces planned and unplanned downtime for the business.
The impact of a disaster is often measured in terms of Recovery Point Objective (RPO – i.e. how much data can a business afford to lose in the event of a disaster) and Recovery Time Objective (RTO – i.e. how much time a business can afford to be down in the event of a disaster). With Oracle Data Guard, when Maximum Protection is used in combination with Real Time Apply, businesses get the benefits of both zero data loss as well as minimal downtime in the event of a disaster and this makes Oracle Data Guard the only solution available today with the best RPO and RTO benefits for a business.
Integration with Flashback Database:
Data Guard in 10g has been integrated with the Flashback family of features to bring the Flashback feature benefits to a Data Guard configuration.One such benefit is human error protection. In Oracle9i, administrators may configure Data Guard with an apply delay to protect standby databases from possible logical data corruptions that occurred on the primary database. The side-effects of such delays are that any reporting that gets done on the standby database is done on old data, and switchover/failover gets delayed because the accumulated logs have to be applied first. In Data Guard 10g, with the Real Time Apply feature, such delayed-reporting or delayed-switchover/failover issues do not exist, and – if logical corruptions do land up affecting both the primary and standby database, the administrator may decide to use Flashback Database on both the primary and standby databases to quickly revert the databases to an earlier point-in-time to back out such user errors.
Another benefit that such integration provides is during failovers. In releases prior to 10g, following any failover operation, the old primary database must be recreated (as a new standby database) from a backup of the new primary database, if the administrator intends to bring it back in the Data Guard configuration. This may be an issue when the database sizes are fairly large, and the primary/standby databases are hundreds/thousands of miles away. However, in Data Guard 10g, after the primary server fault is repaired, the primary database may simply be brought up in mounted mode, “flashed back” (using flashback database) to the SCN at which the failover occurred, and then brought back as a standby database in the Data Guard configuration. No re-instantiation is required.
SQL Apply New Features:
Zero Downtime Instantiation:
Logical standby database can now be created from an online backup of the primary database, without shutting down or quiescing the primary database, as was the case in prior releases. No shutdown of the primary system implies production downtime is eliminated, and no quiesce implies no waiting for quiescing to take effect and no dependence on Resource Manager.
Oracle Database 10g supports database software upgrades (from Oracle Database 10g Patchset 1 onwards) in a rolling fashion, with near zero database downtime, by using Data Guard SQL Apply. The steps involve upgrading the logical standby database to the next release, running in a mixed mode to test and validate the upgrade, doing a role reversal by switching over to the upgraded database, and then finally upgrading the old primary database. While running in a mixed mode for testing purpose, the upgrade can be aborted and the software downgraded, without data loss. For additional data protection during these steps, a second standby database may be used.
By supporting rolling upgrades with minimal downtimes, Data Guard reduces the large maintenance windows typical of many administrative tasks, and enables the 24×7 operation of the business.