Database Development Mistakes

EclipseWorld
October 28-30, 2008

Classic Database Development
Mistakes
Mi t k
7
And Five ways to Overcome them

Scott Walz
Embarcadero Technologies

2

Agenda
g

• Classic DB Development Mistakes

• Steps to overcome them

• Questions

Classic Database Development Mistakes | © 2008 by Scott Walz – Embarcadero Technologies; made available under the EPL v1.0

3

Marketplace
p
• Data is growing at mind bending speed
• The number and diversity of applications is striving to keep
up with market demand, which is further driving data growth
• More and more people are needed to manage the data and
create the applications
t th li ti
• Nearly 16 million application developers today, growing at
nearly 2 million annually*
• Time to market, quality, and predictability of software systems
continues to plague the software industry
• Customers need tools that address development of the entire
system


4

Classic Mistakes

• Rows returned = Success
• My query is FAST!!
• M query d
My does a l t!
lot!


5

Classic Mistakes

• Rows returned = success
– Sample the results
– Validate the query by breaking it down
– Does the row count pass the test?


6

Classic Mistakes

• My query is fast!
– What is your test data size?
– Have you explained it?
• more later


7

Classic Mistakes

• My query does a lot
– Is the query too complex
– Trying to get back too much data
– Would it serve you better to break it into
smaller queries


8

Overcoming the mistakes
g

• Explain Plan usage
• Index usage
• ANSI-92
ANSI 92 SQL
• Reuse, reuse, reuse
• Query rewrites
• Database Structure
• Develop a set of best practices


9

Words of Wisdom
“Several factors determine how well a query performs, some with
greater influence th others. Wh you t
t i fl than th When tune a d t warehouse, it
data h
makes sense to address the factors of greatest influence before those
with lesser influence. Often, the factors with greatest influence
determine performance. When you follow this approach you maximize
performance approach,
the payoff (better query performance) and minimize the effort.
Simply put, this approach takes advantage of the 80/20 rule (law of
diminishing returns) which says that eighty percent of the benefits come
from twenty percent of the effort. If you know what falls into the twenty
percent, take advantage of this knowledge and save yourself a lot of
effort ”1
effort.

1IBM Software Information Center www.ibm.com


10

Explain Plan Usage
p g
• Your window into the database
• The last thing executed before moving the
SQL statement off of your desk.


11

Explan Plan Usage
p g
Looking for Index Usage

Determine the Cost


12

Index Usage
g

• Dramatic performance improvements
• Remember, too many may not be good.


13

Index usage
g

Cost = 0

Cost = 3


14

Syntax Issues
y
• Null Operators

•Sbtf
Substr functions
ti


15

Syntax Issues
y
• Functions suppress index usage

•I
Incompatible d t t
tibl datatypes suppress i d usage
index


16

Syntax Issues
y
• Massaging the query


17

Using ANSI-92 Syntax
g y

• Easier to read
• More companies are standardizing on it


18

Non ANSI-92


19

ANSI-92 SQL


20

Reuse, Reuse, Reuse
, ,

• Take advantage of
– Stored Procedures
– Triggers
– Packages


21

Query Rewrites
y

• There is more than one way to write the
query
– Change the order of the where clause
– Use sub-selects in the place of sub-queries


22

Database Structure

• Could a View be a better option
– If the same tables are queried often w/
changing fields being returned
– A complex query can be optimized once and
a view created based on the query.
– Oftentimes is not a developer option.
• Can be sugges ed, bu normally a DBA ac
Ca suggested, but o a y activity.
y


23

Best Practices


24

Questions

(shameless plug)

www.embarcadero.com
www embarcadero com


Database Development Mistakes

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