Natural Born Killers, Performance issues to avoid
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SQL Server is now a mature RDBMS platform. In this session Richard Douglas walks through a number of areas of the product that are misused or misunderstood. The session promotes good table and index design as well as when to use temporary tables and table variables.
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Natural Born Killers, Performance issues to avoid
- 1. Natural Born Killers, performance issues to avoid Richard Douglas
- 2. Natural Born Killer http://www.flickr.com/photos/merille/4747615138/sizes/z/in/photostream/ 2 Natural Born Killers
- 5. Adhering to best practices? http://www.flickr.com/photos/12693492@N04/1338123903/sizes/m/in/photostream/ 5 Natural Born Killers
- 6. Your host • Richard Douglas • 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 • Table Design • Scalar UDF’s • Indices • Key lookups • Sargability • Table variables • Parameter sniffing 7 Natural Born Killers
- 8. Statistics • SQL uses a 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
- 11. Example of bad design 11 Natural Born Killers
- 12. Example of a better design 12 Natural Born Killers
- 13. Table Design – Size comparison 13 Natural Born Killers
- 14. Good table design benefits • 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 Defined Functions • 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 Solutions and 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
- 19. Indexing strategies It’s all about 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 for Clustered 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 for NonClustered 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 • What is 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
- 28. Summary • Statistics • Table Design • Scalar UDF’s • Indices • Key lookups • Sargability • Table variables • Parameter sniffing 31 Natural Born Killers
- 29. Any questions? 32 Understanding Indices Dell Software
Editor's Notes
- You should know data and workloadI can help you learn more about the internals