XML In My Database!

XML in My Database!
Implementation on a Live e-Store
Using SQL Server 2005
Denise McInerney
Silicon Valley SQL Server User Group
August 19, 2008

August 19, 2008 Denise McInerney 2
Agenda
 Introduction
 XML Native Data Type Overview
 Project Definition
 Decision to Use XML Data Type
 Design Choices
 Getting Data In and Out
 Impact on Performance & Maintenance
 Q & A

Introduction
 10 years SQL Server DBA
 Currently Staff Development DBA
at Intuit
 Web-based OLTP applications
 Design
 Performance Tuning
 MCDBA/MCTS
 PASS volunteer
 Women in Technology SIG Chairperson

PASS Community Summit 2008
 November 18-21, 2008
Washington State Convention & Trade Center,
Seattle
 Over 100 sessions, 4 Tracks
 DBA, App Dev, BI, Professional Development
 MVPs, Microsoft Development Team
 Itzik Ben-Gan, Kalen Delaney, Kimberley Tripp,
Greg Low, Brian Knight, Brad McGehee, Joe Webb,
Kevin Kline
 Many Networking Opportunities
 Vendor Expo
 http://summit2008.sqlpass.org/

Agenda
 Introduction
 Design Choices
 Q & A

XML Data Type Overview
 Introduced in SQL Server 2005
 Allows storage of XML documents in database
 Before SS 2005
 Store in text columns
 Shredded into relational structures
 Produced using FOR XML
 Define a column or variable as XML
CREATE TABLE T1
(Col1 int, Col2 xml)
 Will behave like other data types, mostly
 Can query with XML data type methods
 Can be validated against an XML schema

XML Data Type Overview
 XML data type not a replacement for
relational structure
 Appropriate for
 semi- or unstructured data
 containment hierarchy, instead of
references among entities
 Large object storage (documents)
 Platform independence, data portability
 See Books Online for more

Agenda
 Introduction
 Reason for Using XML
 Design Choices
 Q & A

Project Definition
 Existing e-commerce system
 ~4 million orders
 Front-end application being completely
rewritten
 Opportunity to change the data model

Project Definition
 What is the data?
 Custom printed products
 Contents—what is printed
 Name, address, etc.
 Descriptors—how it’s printed
 Location on item, font face, color, size
 Every product different
 New products introduced regularly

Project Definition
 Stored in HUGE relational tables
 Nested 5 deep
 3 sets
 1 million – 30 million rows
 Ongoing maintenance & performance
problems
 Existing design did not scale
 Data shared with two external systems

Project Definition

Agenda
 Introduction
 Design Choices
 Q & A

Decision to Use XML Data Type
 Data seemed like it “wanted” to be in
XML
 Data met criteria in Microsoft
recommendation
 Hierarchical
 Structure changes
 Needed to be portable
 New application design based on using
XML documents

Decision to Use XML Data Type
 Convince the rest of the team
 Present how it could work
 Yes, it can be queried
 No, it will not eat up terabytes
 Proof-of-concept
 Sample XML document in column
 Prove the application can use it

Agenda
 Introduction
 Design Choices
 Q & A

Design Choices
 Define what is in & what is out
 Very important choices
 XML schema definition determined by needs
of application
 Everything else up for discussion
 Know your WHEREs
 99% of queries based on ID
 ID gets its own column
 Create & update dates also
 Everything else in XML doc/column

Design Choices
 Redundant data?
 In XML column and relational table
 Determined to be necessary in one case
 Be careful here!
 To Bind or Not to Bind?
 Decided “no”
 Many XML schemas, more to come
 Application doing validation

Design Choices
 Final table had 4 columns
 Three tables, one design
 One for work-in-progress
 One for customer-initiated save
 One for final product
 “Final” insert validated against XSD

Design Choices
 Index on XML?
 Can improve performance, can be costly
 Decided not necessary
 All queries first based on PK
 Return small number of rows
 Less XML to be shredded

Agenda
 Introduction
 Design Choices
 Q & A

Getting Data In
 For new records, simple insert
 Entire XML doc in column
 Existing 4 million records, not so simple
 Data had to be preserved, available to
customers right away
 Some bad data existed
 Data conversion biggest challenge

Getting Data In
 Started with FOR XML query
 Tried to create XML doc as defined by
XSD
 Table design made FOR XML difficult
 FOR XML
 Column name = element or attribute name
 Data = element or attribute value
 In relational tables, 1 column contained
name, 1 column contained value
 Painstaking process, slow performance

Getting Data In
 Realized SQL alone was not right tool
 Better answer through collaboration
 Used FOR XML to get relational to XML
 Used code to transform 1st XML to final
XML document

Getting Data In
 Lots of trial and error
 Broke it into pieces
 Bad data
 Many different use cases
 Phased approach
 Did bulk of conversion before launch
 Night of launch ~10,000 records to convert
 Prepared for problems
 Preserved data at every stage of conversion
 Needed it when bugs arose
 Collaboration with developer & production
DBA crucial to success

Getting Data Out
 Most very simple SELECT
SELECT xml_col
WHERE id_col = myID
 Some use of VALUE method
 Retrieves value of element or attribute
 Great performance
 Fixing bugs
 MODIFY method

Agenda
 Introduction
 Design Choices
 Impact on Performance &
Maintenance
 Q & A

Impact on Performance &
Maintenance
 In production 9 months
 Query performance much better
 No timeouts
 Index maintenance problems
eliminated
 Database shrunk

Impact on Performance &
Maintenance
 BEFORE
 Relational Tables + Indexes
 77.5 Gigabytes
 AFTER
 Table with XML column + PK index
 20 Gigabytes
 74% reduction in used space

Agenda
 Introduction
 Reason for Using XML
 Design Choices
 Q & A

Additional Resources
 Books OnLine
 http://msdn.microsoft.com/xml/default.aspx?
pull=/library/en-
us/dnsql90/html/sql2k5xml.asp
pull=/library/en-
us/dnsql90/html/sql2k5xmloptions.asp
pull=/library/en-
us/dnsql90/html/sql25xmlbp.asp
 MS Newsgroups, SQLJunkies.com,
SQLTeam.com…and every SQL Server site
 Contact me: denise.mcinerney@sqlpass.org

XML In My Database!

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