Database Development Mistakes

EclipseWorldOctober 28-30, 2008

Classic Database Development Mi t kMistakes

And Five ways to Overcome them7

And Five ways to Overcome them

Scott WalzEmbarcadero Technologies

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Agendag

• Classic DB Development MistakesClassic DB Development Mistakes

Steps to overcome them• Steps to overcome them

• Questions

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

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Marketplacep• Data is growing at mind bending speed• The number and diversity of applications is striving to keepThe 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

t th li ticreate the applications• 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• Customers need tools that address development of the entire

system


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Classic Mistakes

• Rows returned = SuccessRows returned = Success• My query is FAST!!

M d l t!• My query does a lot!


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Classic Mistakes

• Rows returned = successRows returned = success– Sample the results

Validate the query by breaking it down– Validate the query by breaking it down– Does the row count pass the test?


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Classic Mistakes

• My query is fast!My query is fast!– What is your test data size?

Have you explained it?– Have you explained it?• more later


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Classic Mistakes

• My query does a lotMy query does a lot– Is the query too complex

Trying to get back too much data– Trying to get back too much data– Would it serve you better to break it into

smaller queriessmaller queries


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Overcoming the mistakesg

• Explain Plan usageExplain Plan usage• Index usage

ANSI 92 SQL• ANSI-92 SQL• Reuse, reuse, reuse• Query rewrites• Database StructureDatabase Structure• Develop a set of best practices


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Words of Wisdom“Several factors determine how well a query performs, some with

t i fl th th Wh t d t h itgreater influence than others. When you tune a data warehouse, it 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 maximizedetermine performance. When you follow this approach, you maximize 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 comediminishing 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 ”1effort.


1IBM Software Information Center www.ibm.com

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Explain Plan Usagep g• Your window into the database• The last thing executed before moving the

SQL statement off of your desk.


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Explan Plan Usagep gLooking for Index Usage

Determine the Cost


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Index Usageg

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


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Index usageg

Cost = 0

Cost = 3


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Syntax Issuesy• Null Operators

S b t f ti• Substr functions


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Syntax Issuesy• Functions suppress index usage

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


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Syntax Issuesy• Massaging the query


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Using ANSI-92 Syntaxg y

• Easier to readEasier to read• More companies are standardizing on it


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Non ANSI-92


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ANSI-92 SQL


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Reuse, Reuse, Reuse, ,

• Take advantage ofTake advantage of– Stored Procedures

Triggers– Triggers– Packages


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Query Rewritesy

• There is more than one way to write theThere is more than one way to write the query

Change the order of the where clause– Change the order of the where clause– Use sub-selects in the place of sub-queries


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Database Structure

• Could a View be a better optionCould a View be a better option– If the same tables are queried often w/

changing fields being returnedchanging fields being returned– A complex query can be optimized once and

a view created based on the query.a view created based on the query.– Oftentimes is not a developer option.

• Can be suggested, but normally a DBA activity.Ca be sugges ed, bu o a y a ac y


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Best Practices


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QuestionsQuestions

(shameless plug)

www embarcadero comwww.embarcadero.com


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