What is oracle database instance?

Oracle instance comprises of oracle Memory structures and background process’s (pmon,smon,dbwr,lgwr, ckpt and others)

Oracle Memory structures consists of System Global area and Program Global area.

1. System Global area is allocated at instance startup and is fundamental component of Oracle instance. SGA consists of several memory structures :

-shared Pool

-database Buffer cache

-redo log Buffer

-lock and latch management and other statistical data.

2.Program Global area is allocated when the sever process is started

How to check if Oracle database is running in Archive Log mode:

SQL> archive log list;

Database log mode Archive Mode

Automatic archival Disabled

Archive destination /u01/app/oracle/product/9.2.0/dbs/arch

Oldest online log sequence 568

Next log sequence to archive 569

Current log sequence 570