Oracle Dataguard Flashcards
What is dataguard?
- Oracle DataGuard is the most effective and comprehensive data availability, data protection, and disaster recovery solution for enterprise databases.
- It uses one or more synchronized standby databases to protect data from failures, disasters, errors, and corruptions.
What is Data Guard broker?
- It is a distributed framework that automates and centralizes the creation, maintenance, and monitoring of dataguard configurations.
- Can be accessed through OEM or dgmgrl CLI.
What is the difference between dataguard and standby database?
- Dataguard is set up between the primary and standby instance. It can manage both instances and is only available on Enterprise Edition.
- Standby database provides a physically identical copy of the the primary database. It recovers the redo data received from the primary DB and applies it to the standby. Only available on the Standard Edition.
What are the differences between physical and logical standby databases? How would you decide which one is best suited for your environment?
- Physical standby is physically identical to the primary database and can only be opened in read mode. It is best for high availability solutions and is mostly used for disaster recovery.
- Logical standby is logically identical to the primary database. It transforms redo logs into SQL statements and applies them to the logical DB. It can be opened in read/write. It is best for queries, summations, and reporting activities.
Explain Active Dataguard
It enables read-only access to a physical database for queries, sorting, reporting, web-based access, etc. while continuously applying changes received from production database. It also enables the use of fast incremental backups when offloading backups to a standby database and can provide additional benefits of high availability and disaster protection.
What is a snapshot standby database?
A snapshot database is a fully updatable standby DB that is created by converting a physical database into a snapshot standby DB. It receives and archives the redo data from a primary DB but does not apply the data it receives until it is reverted back to the primary DB.
What does the Dataguard Architecture consist of?
- Primary Database
- Standby Database
- Log Transport Services
- Network Configuration
- Log Apply Services
- Role Management Services
- Dataguard Broker
What are the services required on the standby database?
- Log Writer Process (LGWR)
- Archiver Process (ARCn)
- Fetch Archive Log (FAL) Server
- Fetch Archive Log (FAL) Client
- Remote File Sever (RFS)
- Managed Recover Process (MRP)
What is the Log Writer Process (LGWR)?
It collects redo information and updates the online redo logs.
What is the Archiver Process (ARCn)
- Its one or more processes that makes copies of online redo logs either locally or remotely for standby databases.
- Archives the standby redo logs applied by the managed recovery process (MRP).
What is the Fetch Archive Log (FAL) Server?
It services requests for archive redo logs from FAL clients running on multiple standby databases.
What is the Fetch Archive Log (FAL) Client?
It pulls archived redo logs from the primary site. Initiates transfer of archive redo logs when it detects a gap sequence.
What is the Remote File Server (RFS)?
Receives archived and/or standby redo logs from primary DB.
What is the Managed Recovery Process (MRP)?
Applies archive redo log info to the standby DB.
What are the protection modes in Dataguard?
1) Maximum Protection: offers highest level of data protection. Ensures no data loss even in the event of multiple failures.
2) Maximum Availability: similar to max protection in addition to zero data loss in the event of a single failure.
3) Maximum Performance: highest performance with slightly less data protection on the primary database.
