In this tutorial we learn what is oracle instance and what is oracle database.Below picture will help you to know about oracle instance and oracle database.
Oracle instance:
Oracle instance combination of background process such as (dbwr,lgwr,ckpt,pmon,smon and so on) and allocated memory (SGA) which is used by the oracle database. Background process will help to feed the data into oracle database.
One oracle database can associate with more than one instance but oracle instance must have atleast one database,not more than one database.
Oracle Database:
Oracle database is collection of many files such as (datafiles,logfiles,redo log files,archivelog files,control files,password file,parameter files) which located on the filesystem of the hard drive.
When you startup oracle instance it starts the background process as per written in the parameter file and allocated memory as per written in parameter file. When we shutdown the oracle instance it will deallocated memory and stop all required process but oracle database is collection of physical files which remain same on the server. There will be no impact on the oracle database.
Physical structure of oracle database consists of datafile, redo log file and control file.
Datafile:- Datafile is a physical file which stored in physical disk and is used to store the data .
Redo log file:- Redolog file is also physical file which is stored in physical disk and record all changes made to data. It is used to recover database.
Control file:- It is also physical file which stored on the physical disk . And it records datafile information and redo information .
Logical structure of oracle database consists of data blocks, extents , segment and table space.
Data blocks: It is defined by no of bytes on the physical disk. Oracle data is stored into the data blocks. Defaults size of data blocks is 8 bytes.
Extents: it is combination of many data blocks.
Segment: segment makes using no of extents to create logical storage structure.
Tablespace: data file stores into the table space.one or many datafile is stored into one table space .
In the next tutorial we know about all required background process which will help to feed data into the oracle database.
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