What is an instance of Oracle?

Oracle instance refers to the collective name of Oracle memory structure (SGA) and Oracle process. It is a series of complex memory structures and operating system processes; at any time, an Oracle instance can only be connected to one database. association.

The operating environment of this tutorial: Windows 7 system, Oracle 11g version, Dell G3 computer.

What is an Oracle instance?

Oracle instance refers to the collective name that is composed of the Oracle memory structure (SGA) and the Oracle process. The Oracle database we often refer to refers to the Oracle database management system, which is composed of the Oracle database (data storage) and instances that manage the database.

Oracle instance is Oracle using the background memory structure (SGA) and processes to manage the Oracle database and provide services at the same time. We can make a popular metaphor and compare the Oracle database management system to a warehouse. The database (physical storage, data files, log files, etc.) is the goods and accounting books in the warehouse. The Oracle instance is the department responsible for guarding the warehouse, picking up goods, opening and locking the doors.

Database instance, including database background process (PMON: process monitoring, SMON: system monitoring, DBWR: database reading and writing, LGWR: log reading and writing, CKPT: checkpoint, etc.) and memory area SGA (including shared pool: shared pool, db buffer cache: database cache, redo log buffer: redo log cache area, DC: data dictionary cache, etc.).

Oracle instance is a series of complex memory structures and operating system processes. An Oracle instance can only be associated with one database at any time, just like a door can only enter one database warehouse. But a database can have multiple instances, just like a warehouse may have multiple doors.

Recommended tutorial: "Oracle Tutorial"

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