Oracle logical structures

Oracle logical structures can be summarised by the following:
Schema. Tablespace. Datablock. Redo log.

Schema

• collection of objects (table, view, etc)
• owned by db user
• name is the same as db user
• mixed up (user is often used interchangeably with schema)
• access – user has access to all objects in schema
• name – user only has access to schema of the same name

Tablespace

• Logical storage units – oracle divided into one or more logical storage units
• objects – tablespace stores related database objects
• access – tablespace can be online (accessible) or offline (not accessible)
• normally online so users can access data

Datablock

Tablespace > Segment > Extent > Data block

• tablespace made of one or more segments.
• segments made of one or more extents.
• extents made of one or more data blocks.
• data block id the smallest logical unit oracle can use or allocate.
• block size can be specified at db creation.
• block size should be a multiple of o/s block size.

Redo Log

• 1 or more redo logs per database
• record for recovery – records all actions in case of failure so that data can be recovered.
• duplicate disks – redo logs stored on multiple disks incase og failure due to redo log itsself.
• crash changes – if data cant be written to datafile due to failure then changes can be recovered from redo log so that no data is lost.

see: Oracle process overview

sources: oracle database documentation