Defensive ETL

Tim MitchellArtis Consulting

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Session Objectives

• What is Defensive ETL?• Review threats and challenges• Discuss countermeasures in SSIS

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Tim Mitchell

• Business Intelligence Consultant – Artis Consulting, Dallas TX

• Contributing author, MVP Deep Dives 2• Coauthor, SSIS Design Patterns• SQL Server MVP• TimMitchell.net | Twitter.com/Tim_Mitchell

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Housekeeping

• Questions• Surveys

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Common Data Challenges

• Accidental– Data corruption– Data loss– Transactional inconsistency

• Malicious– Data theft– SQL injection

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Common Data Challenges

• System– Hardware/software failures unrelated to the

operation of the ETL– Unexpected downtime– Resource contention

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ETL Challenges

• Data sources/destination challenges– Inconsistent types– Inconsistent lengths– Unreliable connections– Just plain bad data

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ETL Challenges

• Transformation challenges– Business logic errors– Generated duplicates– “Lost” data– Time allotment overrun

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What Is Defensive ETL?

Two universal truths:• I’m doing it right.• Everybody else is crazy.

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What Is Defensive ETL?

Assumptions of a Defensive ETL professional:• Any input/output over which I do not have

complete control cannot be trusted.• Any process that relies on either hardware or

software cannot be trusted.• Murphy’s Law is inescapable

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Defensive ETL in SSIS

Multifaceted approach:• Package• Sources/destinations• Transformations• Error/event handling• Restartability• Validation

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Defensive ETL in SSIS

Package-Level Defenses

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Defensive ETL in SSIS

Transactions• Package,

container, and/or task

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Defensive ETL in SSIS

Checkpoints• Task or

container level restart

• Avoid use with transactions

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Defensive ETL in SSIS

Logging

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Defensive ETL in SSIS

ETL Framework• Structured approach• Shared logging and

error handling• Restartability

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ETL

Cont

rolle

r

Defensive ETL in SSIS

Event Handling

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Defensive ETL in SSIS

Control Flow Defenses

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Defensive ETL in SSIS

Precedence Constraints• Alternate paths

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Defensive ETL in SSIS

Script Task• Wait/pause• Retry

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Defensive ETL in SSIS

Data Flow Defenses

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Defensive ETL in SSIS

Connections• Metadata is

configurable for some connection types

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Defensive ETL in SSIS

Data Sources• Error or

Truncation• Column by

column

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Defensive ETL in SSIS

Inline Cleansing• Conditional Split• Derived Column

transform

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Defensive strategies

• Incoming data– Inline cleansing– Post-ETL cleansing– Third-party cleansing• DQS in SQL Server Denali

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Defensive strategies

• Incoming data– Data type/length compensation– Loops/retry

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Defensive strategies

• Transformations– Error/lookup outputs– Branching– Rowcount validations

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