Ticking Timebombs in Your Data Models

Thomas LaRock, Solarwinds

Karen Lopez, InfoAdvisors

Know them, fix them, prevent them

Karen López

Karen has 20+ years of data and information architecture experience on large, multi-project programs.

She is a frequent speaker on data modeling, data-driven methodologies and pattern data models.

She wants you to love your data.

A Little About Me…

Thomas has over 15 years experience in roles including programmer, developer, analyst, and DBA.

He is a frequent speaker, published author, and avid blogger on data related technologies.

He enjoys working with data, probably too much to be healthy, really.

Yes, Please do Tweet/Share today’s event

@datachick #heartdata

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Slides

Recording

…next week…

POLL: Who Are You?

Aug 2014

POLL: On Call?

Aug 2014

Agenda

1.Issue

2.Background

3.Story Telling

4.What to do

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MichaelJSwart.com

Primary Scope: Transactional Designs

Time constraints

Designs differ depending on usage of data

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What’s a time bomb?

Perfectly fine design choice

Can be misused

Often leads to 3 AM on-call event

Often misunderstood

Needs monitoring and care

Ready?

Identities

Issue: How people use them

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25532,767

9,223,372,036,854,775,807

2,147,483,647

IDENTITY [ (seed , increment) ]

What could go wrong?

Message: Arithmetic overflow error converting IDENTITY to data type int.

Uncommittable transaction is detected at the end of the batch. The transaction is rolled back.

Identities

Issue: How people monitor them

IDENTITY [ (seed , increment) ]

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How do you fix it if it’s already gone off?

RESEED

GAPS

Not UNIQUE?

Change DataType

We have a script (for SQL server)!

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http://thomaslarock.com/2015/11/sql-server-identity-values-check/

What About SEQUENCEs?

CREATE SEQUENCE [schema_name . ] sequence_name[ AS [ built_in_integer_type | user-defined_integer_type ] ] [ START WITH <constant> ] [ INCREMENT BY <constant> ] [ { MINVALUE [ <constant> ] } | { NOMINVALUE } ]

[ { MAXVALUE [ <constant> ] } | { NOMAXVALUE } ] [ CYCLE | { NOCYCLE } ] [ { CACHE [ <constant> ] } | { NO CACHE } ] [ ; ]

How do you fix it if it’s already gone off?

RESTART

GAPS

Not UNIQUE?

Change DataType

RESTART

ALTER SEQUENCE [schema_name. ] sequence_name

[ RESTART [ WITH <constant> ] ]

[ INCREMENT BY <constant> ]

[ { MINVALUE <constant> } | { NO MINVALUE } ] [ { MAXVALUE <constant> } | { NO MAXVALUE } ]

[ CYCLE | { NO CYCLE } ] [ { CACHE [ <constant> ] } | { NO CACHE } ]

[ ; ]

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How do you prevent it?

Proper Design

Do the math

SEED Value

Increment Value

Use another feature

Monitor

Max allowable value

Max current value

Gaps

Predict* countdown timer

Team Data Script

Know your hottest tables

Prioritize

Datatypes

• Issue: Are you real-world proof?

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CREATE TABLE dbo.customer(CustomerID int PRIMARY KEY NOT NULL,

EmailAddress varchar(25) NULL)

What could go wrong?

Wrong datatype

ZIPCode

López

Account Number

Wrong Length/Precision

karenmariadeguadalupeannlopezymartinez@torontolab.contractor.restricted.reallylongdomainnameherereal

lyreally.com

How do you fix it if it’s already gone off?

ALTER Column

Extended Alter

How do you prevent it?

Proper Design

Do the math

Do research

User Engagement

Go long

Data Profiling

Legacy data

Statistical analysis

Edge cases

Get out a little

DeNormalization

Issue: Denormalizations blow up

•Repeating columns instead of child table

•“Manually” Calculated data

•Roll up, Roll down

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Simple Denormalization

• CREATE TABLE customer(CustomerID int,LastName varchar(255),FirstName varchar(255),EmailAddress varchar(50),

• EmailAddressTwo varchar(255),

• EmailAddressThree varchar(255));

What could go wrong?

SELECT *

Issue: How people use them

• SELECT * FROM ….

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What could go wrong?

SELECT *

Issue: How people monitor them

GovernanceReviewsScriptsTools

How do you fix it if it’s already gone off?

Fix the source table

Fix the query

Fix the target table

Throw out your ORM

Do you have a McGuyver Moment?

Defuse a bomb at 3AM?

Your Time Bombs

What went wrong? How did you fix/prevent it?

Other Time Bombs

• Collations

• Running out of storage space

• Bad Backups (ergo, no restores)

• Mutually dependent tables

• Using deprecated features in new designs

• Accepting a “just for now server”

• Triggers Firing

• Real world scaling (Dev vs. Prod)

• Linked Servers & Nested Views

• Bucket Columns (Bad DEV!)

• VM Snapshots

• Wrong SQL Server License…or “over installed”

• Installing external script without understanding license.

• Server Settings (whole other hour!)

• Faux NULLs

• GenerationNEXT installation process

• Multi-tenant DB Design

• Clustering on Unique Key

• GUIDs when SEQUENCES might do

• SELECT *

• Use of ORMs (generated DML)

Finally…

These are perfectly fine design decisions, but..

• Fully implemented

• Monitored and managed

• Fully understood

• Emergency response plans needed

• Sometimes a paper clip and a stick of gum is not enough (Sorry McGuyver)

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Thank you, you were great.

Let’s do this next month!

Karen Lopez @datachick

#heartdata

Resources

IDENTITY Script:

http://thomaslarock.com/2015/11/sql-server-identity-values-check/

• Karen’s Blog: www.datamodel.com

• Tom’s Blog: www.thomaslarock.com

Thank you!

You were GREAT!

….We should do this again….