SELECT TOP (?) * FROM [50 Things All SQL Server Developers Need To Know] Aaron Bertrand, Senior Consultant

Transcription

1 SELECT TOP (?) * FROM [50 Things All SQL Server Developers Need To Know] Aaron Bertrand, Senior Consultant SQL Sentry, LLC

2 Thank You Presenting Sponsors Gain insights through familiar tools while balancing monitoring and managing user created content across structured and unstructured sources. Idera is a leading provider of IT performance monitoring solutions. Supporting Sponsors Solutions from Dell help you monitor, manage, protect and improve your SQL Server environment. 2

3 Aaron Bertrand Bio Aaron Bertrand is a senior consultant for SQL Sentry, makers of performance monitoring and event management software for SQL Server, Analysis Services, and Windows. He blogs at sqlperformance.com, has been a Microsoft MVP since 1997, will soon be a four-time SQL Cruiser, and speaks frequently at various community events. You can find his MVP profile at: blogs.sqlsentry.com/author/ AaronBertrand

4 A Preview of My Pre-Con Random selections from these areas: Development environment configuration Database design Transact-SQL Query tuning

5 Development Environment Configuration

6 Development Environment Develop on Standard Edition when possible Prevents surprises in production Develop on case sensitive collation when possible Again, principle of least surprise

7 Development Environment Simulate production Match hardware and data as best as you can Stats-only DBs, undocumented UPDATE STATS commands Simulate slow storage using thumb drives, external drives Simulate slow network (or AGs) with aggressive log shipping Trick optimizer with DBCC SETWEIGHTS/OPTIMIZER_WHATIF

8 Demo : DBCC

9 Database Design

10 Database Design : Sensible Data Types Use sensible data types Date/time data stored as strings or integers DATETIME when DATE/SMALLDATETIME would do Duration stored using TIME data type MAX types for data with known bounds ( , URL) NVARCHAR for postal codes / phone numbers VARCHAR for proper names

11 Database Design : Redundant Data Calculations, Dateparts, Concatenations This is usually premature optimization Disk space is cheap, but I/O and memory not

12 Database Design : Column Stuffing Storing arrays or CSVs in a single tuple Pet names: Max, Roxy, Quigley, Bingo Always think relational Parsing / validation are very cumbersome

13 Database Design : Heaps Pros: Great for bulk loading (create indexes after) Freed space can be reused on delete + subsequent insert Cons: Insert performance can be poor if space is reclaimed Updates lead to forwarding pointers 8-byte RID assigned to every row (RID is file:page:slot)

14 T-SQL Tips

15 T-SQL : Variable Length Types Always specify length / precision / scale For (n)(var)char, decimal/numeric, (var)binary, etc. NVARCHAR = N'bar'; CONVERT(NVARCHAR, N'bar'); GO CREATE PROCEDURE VARCHAR AS GO EXEC = 'flubber'; GO

16 T-SQL : Cursor Options Default cursor options are inefficient and heavy-handed Most cursors don t need these options DECLARE c CURSOR FOR vs. DECLARE c CURSOR LOCAL FAST_FORWARD FOR...

17 T-SQL : Shorthand Avoid shorthand; it is not productivity heaven SELECT DATEPART(y, GETDATE()), DATEPART(w, GETDATE()); GO DATE = GETDATE(); + 1; GO

18 T-SQL : Schema Prefix Always specify schema prefix Being explicit prevents confusion and future-proofs code Without schema, object resolution works harder Can yield multiple query plans for the same query

19 Demo : T-SQL

20 Query Tuning

21 Query Tuning : Red Flags In an execution plan, certain things stand out: Scans (especially large scans that yield few rows) High logical reads Missing index warnings Key / RID Lookups Sort operations Distinct Implicit conversions Spills / spools Unbalanced parallel thread distribution Severe mismatch between estimated and actual rows

22 Query Tuning : Understanding the Optimizer Many trace flags to help understand optimizer s decisions 2363 (2014+) shows stats used and selectivity 2372 shows memory used during optimization phases 2373 (2012+) shows optimization rules and memory 8666 adds info to showplan XML, such as stat thresholds 8675 shows optimization stages and timing

23 Query Tuning : Coercing the Optimizer Many trace flags to bend the optimizer to your wishes 8649 encourages parallel plans 8687 discourages parallel plans 8671/8780/8788/2301 spend more time finding optimal plan 4136 OPTION (OPTIMIZE FOR UNKNOWN) to all queries 4137 uses lowest selectivity with multiple AND predicates 4138 turns off row goals with TOP / FAST <n> / IN / EXISTS

24 Query Tuning : Parameter Sniffing Several ways to thwart parameter sniffing Local variables OPTIMIZE FOR Dynamic SQL OPTION (RECOMPILE)

25 Demo : Parameter Sniffing

26 Like What You ve Heard? Aaron will be presenting at PASS Summit 2015! Preconference Session: 50 Things All SQL Server Developers Need to Know General Session: SQL Sentry's Tools for blogs.sqlsentry.com/author/ AaronBertrand Use discount code 24HOP15 to save $200!

27