Data Files• Data Dictionary META(Users, Schema, Storage)• Data Structures• Access Structures• Procedural Objects

Redo Log Files (min 2)i.e. Exception Handling• Journal File (Recovery/UNDO)• DB changes (DB, Table, Users)(SYS will archive Redo)• Archives used for reviews for Tuning & Capacity planning.

Control Files (min 2)• When DB created(Name & identifier)• File names (data/redo)• Last DB checkpoint – Ref Timestamps + Redos• Changes to DB• Backup Info• Log History• Tablespace Names

Hardware Architecture: Physical Structure

Hardware Architecture: Logical Structure contains:• Redo Log Files & Control Files.• Number of tablespaces (1-255 OS files each plus storage space to impose structure)• Objects allocated to 1 tablespace only.

System Tablespace• Created when DB installed• via CREATE DATABASE• Inc. Data Dictionary• Inc. System Rollback Segment

Tablespace A• Based on size Tablespace B

• Based on size• Space Administration• Space Allocation to user

CREATE DATABASE EXAMPLE:

CONTROLFILE REUSELOGFILE ‘REDO1.LOG’ SIZE 30MB,‘REDO1.LOG’ SIZE 30MB,DATAFILE ‘FILE1.ORA’ 250MB;

CREATE TABLESPACE TADATAFILE ‘FILE1.ORA’ 250MB,DATAFILE ‘FILE2.ORA’ 250MB;

CREATE TABLESPACE TBDATAFILE ‘FILE3.ORA’ 250MB,DATAFILE ‘FILE4.ORA’ 250MB;

+

Commands:DROP TABLESPACE TA i.e. only if empty – unless INCLUDING CONTENTS (privilege reqd.)RE-SIZE, READ-ONLY, OFFLINE

OFFLINE via:ALTER TABLESPACE TA (Default NORMAL, IMMEDIATE, TEMPORARY)

• NORMAL - “checkpoint” executed (all T/space files) – all data in DB flushed to Disk.• IMMEDIATE – no “checkpoint” & offline. Recovery required when back online.• TEMPORARY – “checkpoint” for online T/space files – offline as in IMMEDIATE.

Advantages of Tablespaces:• If hardware error – only 1 tablespace affected.• Efficiency improvement.

TABLESPACE >> Segments >> Extents >> Oracle Data Blocks.

ParameterFile

Archived LogFile

PasswordFile

• DB Instance Defaults• DB Resources• Control Files/Archived Log

Tablespace Types:• TEMP for Sorting (No PERM OBJS)• READ-ONLY inc OBJS can be dropped

Database

Logical Physical

Tablespace Data file

OS blockOracle block

Segment

Extent

Database Storage Hierarchy

TABLESPACE Structure

4 Objects:-• Data Segments• Index Segments• Rollback Segments(Transaction Rollback & Recovery)• Temporary Segments (pre-COMMIT)• Nested TablesSegment creation location depends onAllocation of Tablspaces to user.

CREATE USER DGEO IDENTIFIED BY PASSWORD XCDEFAULT TABLESPACE TATEMPORARY TABLESPACE TAQUOTA UNLIMITED ON TAQUOTA 10MB ON TB;

Segment Creation:

STORAGE ( INITIAL 20MB,NEXT 10MB,

MINEXTENTS 3,MAXEXTENTS 3,

PCTINCREASE 15,FREELISTS 3)

SEGMENT Structure

• To minimise fragmentation.• Allocation of storage space.• “NEXT” segments allocated by System when available space insufficient.• PCTINCREASE = growth factor for each subsequent “NEXT” over previous.• EXTENTS allocated when SEG created/extended/altered.• De-allocated when SEG dropped/altered.

DATA BLOCK Structure = Min units of I/O

Data Block Header –includes Row & Trans Directory

PCTFREE “Free Area”

Data Block “Insert Area”

Minimum Block Space

PCTUSED

Segment Data Blocks defined via:• PCTFREE i.e. kept free, when records inserted, for future trans.• PCTUSED i.e. % of data block space to be used before new D/Block.• INITRANS/MAXTRANS i.e. maximum transactions per Data Block

NB:• Insert Area = new records. Free Area = growth for existing records. Key issue for VARCHAR & VARCHAR2 i.e. have variable lengths e.g “Smith” >> “Arrowsmith” on name change. Thus if data block too small – placed in “Free”.• Where “Free” too small – whole record >> new D/Block and chain-linked to avoid index updating.• PCTFREE should be 50-60% if file volatile.• PCTUSED important to optimise space created by PCTFREE or deletions.• If no free D/Blocks system creates “NEXT” Extent.

RECORD Format

Record has 2 components: Row Header & Row Body.

Col length Column data Col length  etc

Rowheader

Row Body i.e. containing columns – each column has its own header stating its column length

Record Header

No of columns

Cluster index

Chain link

Calculating Table Rows that can be stored in a Data Block:

• Block Space minus block header and PCTFREE• Block Space remaining / Table Row size = No of Table Rows stored.