Chapter 18 Methodology – Monitoring and Tuning the Operational System Transparencies © Pearson Education Limited 1995, 2005 2 Chapter 18 - Objectives  Meaning of denormalization.  When to denormalize to improve performance.  Importance of monitoring and tuning the operational system.  How to measure efficiency.  How system resources affect performance. © Pearson Education Limited 1995, 2005 3 Step 7 Consider the Introduction of Controlled Redundancy To determine whether introducing redundancy in a controlled manner by relaxing normalization rules will improve the performance of the system. © Pearson Education Limited 1995, 2005 4 Step 7 Consider the Introduction of Controlled Redundancy  Result of normalization is a design that is structurally consistent with minimal redundancy.  However, sometimes a normalized database does not provide maximum processing efficiency.  May be necessary to accept loss of some benefits of a fully normalized design in favor of performance. © Pearson Education Limited 1995, 2005 5 Step 7 Consider the Introduction of Controlled Redundancy  Also consider that denormalization: – makes implementation more complex; – often sacrifices flexibility; – may speed up retrievals but it slows down updates. © Pearson Education Limited 1995, 2005 6 Step 7 Consider the Introduction of Controlled Redundancy  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.  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. © Pearson Education Limited 1995, 2005 7 Step 7 Consider the Introduction of Controlled Redundancy  Consider denormalization in following situations, specifically to speed up frequent or critical transactions: – Step 7.1 Combining 1:1 relationships – Step 7.2 Duplicating non-key attributes in 1:* relationships to reduce joins – Step 7.3 Duplicating foreign key attributes in 1:* relationships to reduce joins © Pearson Education Limited 1995, 2005 8 Step 7 Consider the Introduction of Controlled Redundancy – Step 7.4 Duplicating attributes in *:* relationships to reduce joins – Step 7.5 Introducing repeating groups – Step 7.6 Creating extract tables – Step 7.7 Partitioning relations. © Pearson Education Limited 1995, 2005 9 Sample Relation Diagram © Pearson Education Limited 1995, 2005 10 Sample Relations © Pearson Education Limited 1995, 2005 [...]... of denormalization © Pearson Education Limited 1995, 2005 21 Step 8 Monitor & Tune Operational System To monitor operational system and improve performance of system to correct inappropriate design decisions or reflect changing requirements © Pearson Education Limited 1995, 2005 22 Step 8 Monitor & Tune Operational System Number of factors may be used to measure efficiency: Transaction throughput:... 2005 18 Step 7.7 Partitioning relations Rather than combining relations together, alternative approach is to decompose them into a number of smaller and more mannageable partitions Two main types of partitioning: horizontal and vertical © Pearson Education Limited 1995, 2005 19 Step 7.7 Partitioning relations © Pearson Education Limited 1995, 2005 20 Advantages and disadvantages of denormalization © Pearson... required to store database files - No one factor is always correct Have to trade each off against another to achieve reasonable balance 23 © Pearson Education Limited 1995, 2005 Need to understand how the various hardware Step 8 Monitor & Tune Operational System DreamHome wish to hold pictures of properties, and comments that describe main features of property © Pearson Education Limited 1995, 2005 24 ... 1995, 2005 Step 7.6 Creating extract tables Reports can access derived data and perform multirelation 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 Possible to create a single, highly denormalized extract table based on relations required by reports, and allow users to access extract table directly instead of base relations . Chapter 18 Methodology – Monitoring and Tuning the Operational System Transparencies © Pearson Education Limited 1995, 2005 2 Chapter 18.  Importance of monitoring and tuning the operational system.  How to measure efficiency.  How system resources affect performance. © Pearson Education Limited 1995, 2005 3 Step 7 Consider the Introduction. whether introducing redundancy in a controlled manner by relaxing normalization rules will improve the performance of the system. © Pearson Education Limited 1995, 2005 4 Step 7 Consider the