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Natural Born Killers, Performance issues to avoid
Richard Douglas's presentation covers critical topics in SQL Server performance optimization, including table design, statistics, and indexing strategies. He discusses best practices to avoid performance issues and emphasizes the importance of understanding scalar user-defined functions and parameter sniffing. Key takeaways include the significance of sargability and comparing the usage of table variables versus temporary tables for different data sets.
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Natural Born Killers, Performance issues to avoid
- 1. Natural Born Killers, performanceissues to avoid Richard Douglas
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- 5. Adhering to bestpractices? http://www.flickr.com/photos/12693492@N04/1338123903/sizes/m/in/photostream/ 5 Natural Born Killers
- 6. Your host • RichardDouglas • Systems Consultant • SQL Server MCITPro • Maidenhead SQL User Group Leader • Blog: http://SQL.RichardDouglas.co.uk • Twitter: @SQLRich • Email: Richard.Douglas@Quest.com Richard_Douglas@Dell.com 6 Natural Born Killers
- 7. Agenda • Statistics • TableDesign • Scalar UDF’s • Indices • Key lookups • Sargability • Table variables • Parameter sniffing 7 Natural Born Killers
- 8. Statistics • SQL usesa cost based optimizer • Costs influenced by statistics 8 Natural Born Killers
- 9. Statistics • Creating Statistics –Automatic – Manual – CREATE STATISTICS – sp_CreateStats • Updating Statistics Permanent Table Temporary Table 1st record 1st record - 6 records LT 500 recs, 500 changes LT 500 recs, 500 changes GT 500 recs, 500 changes + 20% GT 500 recs, 500 changes + 20% • Sp_UpdateStats • UPDATE STATISTICS 9 Natural Born Killers
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- 11. Example of baddesign 11 Natural Born Killers
- 12. Example of abetter design 12 Natural Born Killers
- 13. Table Design –Size comparison 13 Natural Born Killers
- 14. Good table designbenefits • Minimise the CPU overhead. • Increase the number of records in the buffer cache. • Reduce the amount of physical disk IO. • Reduce the amount of network traffic. • Reduce the data file size(s). • Reduce the working size of the Transaction Log. • Reduce Full/Diff /T-Log backup file size. Thereby increasing your ability to deliver your RTO. • Keep transaction time to a minimum. 14 Natural Born Killers
- 16. Scalar User DefinedFunctions • The Good – Re-Usable code • The Bad – Runs once per record in record set – They don’t take advantage of parallelism – They use Nested Loop joins regardless • The Ugly – So ugly it’s hidden from the query plan and IO statistics 19 Natural Born Killers
- 17. Scalar UDF Solutionsand Alternatives • If you have to use them: – View the actual IO usage in Profiler • If you can replace them: – Look at Table Value Functions – Look at CLR 20 Natural Born Killers
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- 19. Indexing strategies It’s allabout DWI knowledge: D W I a t a 22 Natural Born Killers o r k l o a d n t e r n a l s
- 20. Golden Rules forClustered Indexes Bad example; Surname, Firstname, Middle Initial • Static Impacts nonclustered indexes • Progressive Fragmentation • Narrow • Unique • Fixed width Space impact • Not Null This example will have 13 bytes of overhead alone; • 4 byte uniquifier • 2 byte variable offset + 6 bytes for variable length fields • 1 byte for NULL values and NULL bitmap 23 Natural Born Killers
- 21. Golden Rules forNonClustered Indexes • Have an optimal clustered key • Not narrow • Reduce unnecessary overhead – Fixed Width – Not null • Consolidate • Index foreign keys 24 Natural Born Killers
- 22. Key Lookups –The silent killer 25 Natural Born Killers
- 23. Sargability • SARGable –“Search ARGument able” • T-SQL functions around a predicate can break SARGability • Some caveats to remember 26 Natural Born Killers
- 24. Table Variables Vs.Temp Tables Table Variables • Fast when used with small data sets. • Have a limited scope • Use less locking and logging resources than temp tables – http://sql.richarddouglas.co.uk/archive/2011/06/rollback-gotchaspart-2-2.html • Estimated statistics always show 1 record • Cannot be altered after they are declared • Mythbuster - MAY be memory only, this isn’t guaranteed • Generally faster with smaller data sets 27 Natural Born Killers
- 25. Table Variables Vs.Temp Tables Temp Tables • Uses statistics – Stat population will cause recompiles (statement level in 2005 +) – Can create better plans • Wider scope • Can be rolled back • Can be altered after creation • Generally faster with larger data sets 28 Natural Born Killers
- 26. Parameter Sniffing • Whatis it? – It’s all a matter of statistics • How do I know when it will affect me? – Monitor the IO and CPU – This means baselining your environment • What are my options? – Rewrite dynamic queries – Query Hints: – WITH RECOMPILE – OPTIMIZE FOR – Plan Guides 29 Natural Born Killers
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- 28. Summary • Statistics • TableDesign • Scalar UDF’s • Indices • Key lookups • Sargability • Table variables • Parameter sniffing 31 Natural Born Killers
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Editor's Notes
- #23 You should know data and workloadI can help you learn more about the internals