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© 2012 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION
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Presented by Harsh Chawla
SQL Community Session – Delhi NCR
DBA: Query Tuning and Optimization - Expert
1. DB Consultant Approaches2. Fetching Execution Plans3. Common execution plan patterns4. Understand the data distribution5. Q&A
Welcome.Microsoft Services helps businesses around the world maximize their return on investment in Microsoft products and technologies.
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Proactive Approach • Leverage MDW
• Have a Performance Baseline
Understand the load
• Missing Indexes• Duplicate Indexes• Unused Indexes
Understand the Indexing
• Leverage Plan hash and Query Hash to find top resource intensive queries
• Leverage MDW to identify the top queries
Fetch Top Queries for Tuning
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Reactive Approach
• Leverage MDW /SQLNexus to identify the resource contention
Identify the Top Bottlenecks
• Leverage Plan hash and Query Hash to find top resource intensive queries
• Leverage MDW to identify the top queries
Identify the Top Resource intensive queries
• Set Statistics IO ON• Set Statistics Time on• Set Statistics Profile on
Explore the execution plans
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Fetching Execution plans
• Estimated Vs Actual• DMVs show only estimated
plans• Extract the variables from
the execution plan• Execute the query to get the
actual execution plan
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CommonExecution Plan Patterns
• Index Seek• Index Scan• Key/RID Lookups• Implicit Conversions• Missing Statistics
Warning• Sort Warning• Hash Warning
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Let’s Delve Deeper
• Cardinality Estimation• Residual Predicates• Impact of Data
distribution• Sorts
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Cardinality Estimation
• Beauty lies in the data• There is never a
coincidence• Wrong Estimation cause
Hash warnings/sort warning or almost every mess up
• It’s the biggest gotcha while query tuning
• Try to investigate the numbers
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Demo
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Residual Predicates
• What’s a Predicate• If the predicate is not
SARGable, Residual Predicates will be seen
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Demo Impact of data distribution
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Demo Sort
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Q&A