Methodology – Monitoring and Tuning the Operational System

2 Step 8 Consider the Introduction of Controlled Redundancy To determine whether introducing redundancy in a controlled manner by relaxing the normalization rules will improve the performance of the system.

3 Step 8 Consider the Introduction of Controlled Redundancy u Result of normalization is a logical database design that is structurally consistent and has minimal redundancy. u However, sometimes a normalized database design does not provide maximum processing efficiency. u It may be necessary to accept the loss of some of the benefits of a fully normalized design in favor of performance.

4 Step 8 Consider the Introduction of Controlled Redundancy u Also consider that denormalization: –makes implementation more complex; –often sacrifices flexibility; –may speed up retrievals but it slows down updates.

5 Step 8 Consider the Introduction of Controlled Redundancy u Denormalization refers to a refinement to relational schema such that the degree of normalization for a modified relation is less than the degree of at least one of the original relations. u Also use term more loosely to refer to situations where two relations are combined into one new relation, which is still normalized but contains more nulls than original relations.

6 Step 8 Consider the Introduction of Controlled Redundancy u Consider denormalization in following situations, specifically to speed up frequent or critical transactions: –Step 8.1 Combining 1:1 relationships –Step 8.2 Duplicating nonkey attributes in 1:* relationships to reduce joins –Step 8.3 Duplicating foreign key attributes in 1:* relationships to reduce joins

7 Step 8 Consider the Introduction of Controlled Redundancy –Step 8.5 Introducing repeating groups –Step 8.6 Merging lookup tables with base relations –Step 8.7 Creating extract tables.

8 Step 8.7 Creating Extract Tables u Reports can access derived data and perform multi-relation joins on same set of base relations. However, data the report is based on may be relatively static or may not have to be current. u Possible to create a single, highly denormalized extract table based on the relations required by the reports, and allow the users to access extract table directly instead of the base relations.

9 Step 9 Monitor and Tune the Operational System To monitor operational system and improve performance of system to correct inappropriate design decisions or reflect changing requirements.