database design considerations

Database Design Considerations

Oracle specific Design Considerations Data Integrity Issues Performance Considerations Storage Issues

Overview

Why Adapt Data Design?• User Expectations

• Oracle specifics

• Volumes• Hardware• Network• O.S.

AdaptedPhysicalDesign

Initial design

Depending on: Domains Storage issue Performance Use

Select a data type for columns: Character Number Date Large Objects

Oracle Data Types

Primary key columns Unique Key columns Foreign key columns Mandatory columns Optional columns

Large object columns always at the end

Suggested Column Sequence

Primary KeysCREATE TABLE countries( code NUMBER(6) NOT NULL, name VARCHAR2(25) NOT NULL, currency NUMBER (10,2) NOT NULL);ALTER TABLE countries ADD CONSTRAINT cty_pk PRIMARY KEY (code);

Constraint and Index name

Choosing the Right Key Simplicity Ease of use Performance Size Meaningless Stability

Primary Keys

Artificial Keys

DS (D)pkpkpk

fk1 = d_a_fk fk2 = d_b_fk fk3 = d_c_fk

fk = x_d_fk

uuu

pk * Id

,fk1,fk2,fk3

****

A_idB_idC_idC4

pk * Id * C2

BS (B)

XS (X)pkfk1fk1fk1

****o

IdD_a_idD_b_idD_c_idC5

fk * D_id

pk * Id * C3

CS (C)pk * Id * C1

AS (A)

Sequences

CREATE SEQUENCE sequence_nameINCREMENT BY numberSTART WITH numberMINVALUE numberMAXVALUE numberCACHE number | NOCACHECYCLE | NOCYCLE;

223

224225

Restrict

Cascade

Default Nullify

Delete Update

Foreign Key Behavior

Supported by Oracle through declaration

Indexes• Performance

ALBERT 2655

ALFRED 3544

ALICE 7593

ALLISON 3456

ALVIN 8642

ALPHONSO 2841

Name Phone

• Uniqueness

bcdefghijklmnopq

rstuvwxyz

Choosing Indexes

aba .1.2.5abb .1.3.5abc .1.1.5bba .1.4.5. . .

B*tree

aba .1.2.5abb .1.4.5bba .1.3.5cba .1.1.5...

Reverse

YXZXZ

abcabaabbbbabbc

C1 C2

Bitmap

Y10000

X01010

Z00101

XZYZX

abaabbabcbbabbc

I.O.TableC1 C2

Primary key columns and Unique Key columns (Up to Version 6)

Foreign Key columns When significant better performance can be

observed in SELECT statements

Which Columns to Index?

Avoid indexing:

• Small tables• Columns frequently updated

!

When referenced in a Where clause or Order By

When the Where clause does not include some operators

When the optimizer decides With hints in the SQL statement

When Can Indexes be Used?

CUSTOMERSRegionCol1 Col2 Col3

CUSTOMERS_R1RegionCol1 Col2 Col3

CUSTOMERS_R2RegionCol1 Col2 Col3

Partitioning Tables and Indexes

Restricting access Presentation of data Isolate applications from data structure Save complex queries Simplify user commands

Views

T1 T2 T3 T4

V1 V2 V3 V4

Advantages Dynamic views Present denormalized data from normalized tables Simplify SQL statements

Disadvantages May affect performances Restricted DML in some cases

Reasons for Views

Unique index Views with “Check option” clause Generic Arc implementation

Old Fashioned Design

Generic Arc ImplementationA# Id* Name

AS (A)

Y# Id* Name

**

. . . Table_nameFk_id

(X or Y)

X# Id* Name

Different physical databases appear as one logical database.

Distributed Database

Resilience Reduced line traffic Location transparency Local autonomy Easier growth path

but Increased, distributed, complexity

Benefits of Distributed Databases

Database Structure

DATA BLOCK

SEGMENT

DATABASE

DATA FILE

INDEXSEGMENT

TABLESPACE

TABLE OR INDEX PARTITION

EXTENT FREE

TABLESEGMENT

part of

located inpart

of

residence of

part of

consists of

resides in

consists of

container of

consistsofpart

ofpart

of

sliced in sliced in

USED

OTHERSEGMENT

consists of

part of

resides inresidence

of

Data Types Primary, Foreign, and Artificial Keys Indexes Partitioning Views Distributed design

Summary

Data Types Artificial Keys Product Pictures

Practices