Oracle Database
Oracle Database is one product among others forming the Oracle suite (Oracle Database, Oracle Application Server, Oracle Developer Suite, Oracle Enterprise Manager Grid Control…).
Oracle Database is the Oracle database management system that allows multiple users to access data simultaneously while ensuring availability and disaster recovery mechanisms.
Be aware that Oracle Database refers to the entire Oracle software, while database has a specific meaning in the Oracle architecture.
To guarantee a high level of performance, Oracle maintains the database thanks to memory structures (in random access memory: RAM) and physical structures (on hard disk) and uses processes for the storage of data in memory or on disk .
Writing to disk is only performed when necessary and under conditions while Memory is used as much as possible since memory access is faster than disk access (performance gain).
In the event of a power outage, for example, Oracle will be able to recover well if data in memory, at the time of the incident, is not written to disk. This is the recovery of the instance managed by the SMON process discussed later in the oracle architecture.
An instance failure requires recovery, while a physical failure (such as a disk crash) requires a restore followed by a recovery.
Restoration and recovery are two different terms that should be clearly distinguished. The restoration is made from backup files and the recovery allows to reapply to the restored data files, the modifications already made on the base to find the consistent state of the database before the incident.
In the example in the figure, recovery at time t2 requires restoring the last available S1 backup and reimplementing any changes that occurred in the interval t1-t2.
To learn more about the components and basic concepts of the Oracle architecture, take look at our Expert DBA Team Club blog and more advance topics are available at this source.
