RoadToMaster – Basically, there are two main components of Oracle database –– instance and database itself. An instance consists of some memory structures and the background processes, whereas a database refers to the disk resources. Figure 1 will show you the relationship.
Instance
As we cover above, the memory structures and background processes contitute an instance. The memory structure itself consists of System Global Area (SGA), Program Global Area (PGA), and an optional area –– Software Area Code. In the other hand, the mandatory background processes are Database Writer (DBWn), Log Writer (LGWR), Checkpoint (CKPT), System Monitor (SMON), and Process Monitor (PMON). And another optional background processes are Archiver (ARCn), Recoverer (RECO), etc. Figure 2 will illustrate the relationship for those components on an instance. Continue reading
DBA In Seconds 