slide cơ sở dữ liệu tiếng anh chương (18) methodology – monitoring and tuning the operational system transparencies

Chapter 18
Methodology – Monitoring and
Tuning the Operational System
Transparencies
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Chapter 18 - Objectives
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Meaning of denormalization.
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When to denormalize to improve performance.
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Importance of monitoring and tuning the
operational system.
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How to measure efficiency.
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How system resources affect performance.
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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.
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Step 7 Consider the Introduction of
Controlled Redundancy
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Result of normalization is a design that is

structurally consistent with minimal
redundancy.
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However, sometimes a normalized database
does not provide maximum processing
efficiency.
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May be necessary to accept loss of some
benefits of a fully normalized design in
favor of performance.
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Step 7 Consider the Introduction of
Controlled Redundancy
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Also consider that denormalization:
–
makes implementation more complex;
–
often sacrifices flexibility;
–
may speed up retrievals but it slows
down updates.
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Step 7 Consider the Introduction of
Controlled Redundancy
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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.
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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.
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Step 7 Consider the Introduction of
Controlled Redundancy
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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
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Step 7 Consider the Introduction of
Controlled Redundancy
–

Step 7.4 Duplicating attributes in *:*
relationships to reduce joins
–
Step 7.5 Introducing repeating groups
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Step 7.6 Creating extract tables
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Step 7.7 Partitioning relations.
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Sample Relation Diagram
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Sample Relations
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Step 7.1 Combining 1:1 relationships
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Step 7.2 Duplicating non-key attributes in 1:*
relationships to reduce joins
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Step 7.2 Duplicating non-key attributes in
1:* relationships: Lookup Table
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Step 7.2 Duplicating non-key attributes in
1:* relationships: Lookup Table
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Step 7.3 Duplicating FK attributes in 1:*
relationship to reduce joins
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1995, 2005
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Step 7.4 Duplicating attributes in *:*
relationships to reduce joins
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Step 7.5 Introducing repeating groups
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Step 7.6 Creating extract tables
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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.
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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.
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Step 7.7 Partitioning relations
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Rather than combining relations together,
alternative approach is to decompose them

into a number of smaller and more
mannageable partitions.
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Two main types of partitioning: horizontal
and vertical.
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Step 7.7 Partitioning relations
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Advantages and disadvantages of
denormalization
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Step 8 Monitor & Tune Operational System
To monitor operational system and improve
performance of system to correct inappropriate
design decisions or reflect changing requirements.
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Step 8 Monitor & Tune Operational System
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Number of factors may be used to measure
efficiency:
- Transaction throughput: number of transactions
processed in given time interval.
- Response time: elapsed time for completion of a
single transaction.
- Disk storage: amount of disk space required to
store database files.

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No one factor is always correct. Have to trade
each off against another to achieve reasonable
balance.
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Need to understand how the various hardware
components interact and affect database performance.
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Step 8 Monitor & Tune Operational System
DreamHome wish to hold pictures of
properties, and comments that describe
main features of property.
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