SQL server query performance tuning, 4th edition

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www.it-ebooks.info For your convenience Apress has placed some of the front matter material after the index Please use the Bookmarks and Contents at a Glance links to access them www.it-ebooks.info Contents at a Glance About the Author�� xxiii About the Technical Reviewer�� xxv Acknowledgments�� xxvii Introduction�� xxix ■■Chapter 1: SQL Query Performance Tuning��1 ■■Chapter 2: Memory Performance Analysis��17 ■■Chapter 3: Disk Performance Analysis��35 ■■Chapter 4: CPU Performance Analysis��47 ■■Chapter 5: Creating a Baseline��57 ■■Chapter 6: Query Performance Metrics��69 ■■Chapter 7: Analyzing Query Performance ��85 ■■Chapter 8: Index Architecture and Behavior��111 ■■Chapter 9: Index Analysis��143 ■■Chapter 10: Database Engine Tuning Advisor��165 ■■Chapter 11: Key Lookups and Solutions��181 ■■Chapter 12: Statistics, Data Distribution, and Cardinality��193 ■■Chapter 13: Index Fragmentation��237 ■■Chapter 14: Execution Plan Generation��269 ■■Chapter 15 Execution Plan Cache Behavior��283 iii www.it-ebooks.info ■ Contents at a Glance ■■Chapter 16: Parameter Sniffing��311 ■■Chapter 17: Query Recompilation��321 ■■Chapter 18: Query Design Analysis��355 ■■Chapter 19: Reduce Query Resource Use��379 ■■Chapter 20: Blocking and Blocked Processes��397 ■■Chapter 21: Causes and Solutions for Deadlocks��443 ■■Chapter 22: Row-by-Row Processing��459 ■■Chapter 23: Memory-Optimized OLTP Tables and Procedures��483 ■■Chapter 24: Database Performance Testing��505 ■■Chapter 25: Database Workload Optimization��515 ■■Chapter 26: SQL Server Optimization Checklist��547 Index��565 iv www.it-ebooks.info Introduction After all the years of work on SQL Server by Microsoft and all the work put in by talented data professionals, you’d think that fundamental performance problems would be a thing of the past, but they’re not Performance is frequently one of the last things on people’s minds when they’re developing a system Unfortunately, that means it usually becomes the biggest problem after that system goes to production You can’t simply rely on getting a phone call that tells you that procedure X on database Y that runs on server Z is running slow You need to have mechanisms in place to find this information for yourself You also can’t work off the general word slow Slow compared to what? Last week? Last month? The way it ran in your development system? And once you’ve identified something as actually running slow, you need to identify why Does it need an index? Does it have an index that it isn’t using? Is it the CPU, the disk, the memory, the number of users, the amount of data? And now that you’ve identified what and why, you have to something about it How? Rewrite the query? Change the WHERE clause? The questions that will come your way when you start performance tuning are endless This book provides you with the tools you need to answer those questions I’ll show you how to set up mechanisms for collecting performance metrics on your server for the SQL Server instances and databases living there I’ll go over the more tactical methods of collecting data on individual T-SQL calls Along the way, I’ll be discussing index structure, choice, and maintenance; how best to write your T-SQL code; how to test that code; and a whole slew of other topics One of my goals when writing this book was to deliver all these things using examples that resemble the types of queries you’ll see in the real world The tools and methods presented are mostly available with SQL Server Standard edition, although some are available only with SQL Server Enterprise edition These are called out whenever you might encounter them Almost all the tuning advice in the book is directly applicable to Microsoft Azure SQL Database (MASD), as well as to the more earthbound SQL Server 2014 Most of the tuning advice in the book is also immediately applicable to servers running within virtual machines (VMs) The primary differences for both MASD and VMs relate to what performance metrics you can collect and how much trust to put in them The performance solutions that are code and structure related are immediately applicable to both these environments An argument can be made that a lot of the fundamentals for query tuning have not changed radically from SQL Server 2008 to 2012 to 2014 Therefore, the need for a new, updated version of this book may not be immediately clear What has changed over those various releases of SQL Server is where queries run, what metrics are available to understand the system, and what tools you have available to tune your queries The point of this latest update to the book, in addition to adding information about the new functionality available within SQL Server 2014, is to clarify the types of information and responses available on those other environments I’ve taken the opportunity to completely restructure and rename the chapters Several new chapters have been introduced, allowing me to both expand the scope of the material within the book and make it much easier to consume The main point is to learn how to answer all the various questions that are going to be presented to you This book gives you the tools to that and to answer those questions in a methodical manner that eliminates much of the guesswork that is so common in performance optimization today Performance problems aren’t something to be feared With the right tools, you can tackle performance problems with a calmness and reliability that will earn the respect of your peers and your clients That will contribute directly to your success and theirs xxix www.it-ebooks.info ■ Introduction Who This Book Is For This book is for just about anyone responsible for the performance of the system Database administrators, certainly, are targeted because they’re responsible for setting up the systems, creating the infrastructure, and monitoring it over time Developers are too, because who else is going to generate all the well-formed and highly performant T-SQL code? Database devel-opers, more than anyone, are the target audience, if only because that’s what I for work Anyone who has the capability to write T-SQL, design tables, implement indexes, or manipulate server settings on the SQL Server system is going to need this information to one degree or another How This Book Is Structured The purpose of this book was to use as many “real-looking” queries as possible To this, I needed a “real” database I could have created one and forced everyone to track down the download Instead, I chose to use the sample database created by Microsoft, called AdventureWorks2012 This is available through CodePlex (www.codeplex.com/ MSFTDBProdSamples) I suggest keeping a copy of the restore handy and resetting your sample database after you have read a couple of topics from the book Microsoft updates these databases over time, so you might see different sets of data or different behavior with some of the queries than what is listed in this book I chose AdventureWorks2012 not because it represents a perfect database design but because it suffers from a number of design flaws and data distribution issues that make it more accurately reflect the real world instead of some flawless test case To a degree, this book builds on the knowledge presented from previous chapters However, most of the chapters present information unique within that topic, so it is possible for you to jump in and out of particular chapters You will still receive the most benefit by a sequential reading of Chapter through Chapter 26 •• Chapter 1, “SQL Query Performance Tuning,” introduces the iterative process of performance tuning You’ll get a first glimpse at establishing a performance baseline, identifying bottlenecks, resolving the problems, and quantifying the improvements •• Chapter 2, “Memory Performance Analysis,” starts the process using Performance Monitor metrics and dynamic management objects as mechanisms for collecting information about memory on your systems •• Chapter 3, “Disk Performance Analysis,” continues exploring the system of bottlenecks with a chapter dedicated to understanding how to collect metrics on disk performance You’ll use Performance Monitor and dynamic management objects again as well as add a number of additional T-SQL queries •• Chapter 4, “CPU Performance Analysis,” concludes the system bottleneck discussions with CPU I’ll also cover some network monitoring, although that is a fairly rare issue within SQL Server, and there’s little a DBA or developer can about it usually The tools used are the same as in the preceding chapters •• Chapter 5, “Creating a Baseline,” takes the information from all three of the preceding chapters and uses it to define a baseline A baseline represents a known point in your system from which you can compare to understand how performance is changing over time within your system •• Chapter 6, “Query Performance Metrics,” defines the best ways to look “under the hood” and see what kinds of queries are being run on your system It provides a detailed look at the new Extended Events tools Several of the most useful dynamic management views and functions used to monitor queries are first identified in this chapter xxx www.it-ebooks.info ■ Introduction •• Chapter 7, “Analyzing Query Performance,” walks you through consuming the metrics gathered in the previous chapter and shows various methods available to analyze query performance You’re introduced for the first time to query execution plans as well as other utilities available within SQL Server for determining which queries are longest running, most frequently called, or in need of tuning •• Chapter 8, “Index Architecture and Behavior,” explains indexes and index architecture It defines the differences between clustered and nonclustered indexes It shows which types of indexes work best with different types of querying Basic index maintenance is also introduced •• Chapter 9, “Index Analysis,” adds to the information from the preceding chapter and supplies more information about the use and functionality of indexes within SQL Server •• Chapter 10, “Database Engine Tuning Advisor,” covers the Microsoft tool Database Engine Tuning Advisor The chapter goes over in detail how to use the Database Engine Tuning Advisor; you’re introduced to the various mechanisms for calling the tool and shown how it works under real loads •• Chapter 11, “Key Lookups and Solutions,” takes on the classic performance problem, the key lookup, which is also known as the bookmark lookup This chapter explores various solutions to the lookup operation •• Chapter 12, “Statistics, Data Distribution, and Cardinality,” introduces the concept of statistics The optimizer uses statistics to make decisions regarding the execution of the query Maintaining statistics, understanding how they’re stored, learning how they work, and learning how they affect your queries are all topics covered within this chapter •• Chapter 13, “Index Fragmentation,” shows how indexes fragment over time You’ll learn how to identify when an index is fragmented You’ll also see what happens to your queries as indexes fragment, and you’ll learn mechanisms to eliminate index fragmentation •• Chapter 14, “Execution Plan Generation,” presents the mechanisms that SQL Server uses to create execution plans Plan reuse is an important concept within SQL Server You’ll learn how to identify whether plans are being reused You’ll get various mechanisms for looking at the cache This chapter also introduces dynamic management views that allow excellent access to the cache •• Chapter 15, “Execution Plan Cache Behavior,” covers information about how plans move in and out of cache as well as other details about execution plan behaviors including query and plan hash and your ability to reuse execution plans in cache •• Chapter 16, “Parameter Sniffing,” explains the extremely helpful process running automatically within SQL Server called parameter sniffing But, parameter sniffing can go bad and cause serious performance issues The problem, and the solutions, all go back to system statistics •• Chapter 17, “Query Recompilation,” displays how and when SQL Server will recompile plans that were stored in cache You’ll learn how plan recompiles can hurt or help the performance of your system You’ll pick up mechanisms for forcing a recompile and for preventing one •• Chapter 18, “Query Design Analysis,” reveals how to write queries that perform well within your system Common mistakes are explored, and solutions are provided You’ll learn several best practices to avoid common bottlenecks xxxi www.it-ebooks.info ■ Introduction •• Chapter 19, “Reduce Query Resource Use,” demonstrates various methods to ensure you’re using fewer resources such as CPU and I/O when running your queries You’ll learn about a number of antipatterns that you should avoid while writing your T-SQL •• Chapter 20, “Blocking and Blocked Processes,” teaches the best ways to recognize when various sessions on your server are in contention for resources You’ll learn how to monitor for blocking along with methods and techniques to avoid blocked sessions •• Chapter 21, “Causes and Solutions for Deadlocks,” shows how deadlocks occur on your system You’ll get methods for identifying sessions involved with deadlocks The chapter also presents best practices for avoiding deadlocks or fixing your code if deadlocks are already occurring •• Chapter 22, “Row-by-Row Processing,” diagrams the inherent costs that cursors present to set-oriented T-SQL code However, when cursors are unavoidable, you need to understand how they work, what they do, and how best to tune them within your environment if eliminating them outright is not an option •• Chapter 23, “Memory-Optimized OLTP Tables and Procedures,” introduces the new capabilities of in-memory data storage and retrieval You’ll also see how the in-memory stored procedure can radically change performance in a positive fashion But, this technology isn’t universally applicable, so I’ll also go over some of the limitations and best practices for applicability •• Chapter 24, “Database Performance Testing,” provides you with mechanisms to replicate the performance of your production system onto test systems in order to help you validate that the changes you’ve introduced to your queries really are helpful You’ll be using the Distributed Replay utility, introduced in SQL Server 2012, along with all the other tools you’ve been using throughout the book •• Chapter 25, “Database Workload Optimization,” demonstrates how to take the information presented in all the previous chapters and put it to work on a real database workload You’ll identify the worst-performing procedures and put them through various tuning methods to arrive at better performance •• Chapter 26, “SQL Server Optimization Checklist,” summarizes all the preceding chapters into a set of checklists and best practices The goal of the chapter is to enable you to have a place for quickly reviewing all you have learned from the rest of the book Downloading the Code You can download the code examples used in this book from the Source Code section of the Apress web site (www.apress.com) Most of the code is straight T-SQL stored in sql files, which can be opened and used in any SQL Server T-SQL editing tool There are a couple of PowerShell scripts that will have to be run through a PowerShell command line Contacting the Author You can contact the author, Grant Fritchey, at grant@scarydba.com You can visit his blog at http://scarydba.com xxxii www.it-ebooks.info Chapter SQL Query Performance Tuning Query performance tuning remains an important part of today’s database applications Yes, hardware performance is constantly improving Upgrades to SQL Server—especially to the optimizer, which helps determine how a query is executed, and the query engine, which executes the query—lead to better performance all on their own At the same time, SQL Server instances are being put on virtual machines, either locally or in hosted environments, where the hardware behavior is not guaranteed Databases are going to platform as a service systems such as Amazon RDS and Windows Azure SQL Database You still have to deal with fundamental database design and code generation In short, query performance tuning remains a vital mechanism for improving the performance of your database management systems The beauty of query performance tuning is that, in many cases, a small change to an index or a SQL query can result in a far more efficient application at a very low cost In those cases, the increase in performance can be orders of magnitude better than that offered by an incrementally faster CPU or a slightly better optimizer There are, however, many pitfalls for the unwary As a result, a proven process is required to ensure that you correctly identify and resolve performance bottlenecks To whet your appetite for the types of topics essential to honing your query optimization skills, the following is a quick list of the query optimization aspects I cover in this book: • Identifying problematic SQL queries • Analyzing a query execution plan • Evaluating the effectiveness of the current indexes • Avoiding bookmark lookups • Evaluating the effectiveness of the current statistics • Understanding parameter sniffing and fixing it when it breaks • Analyzing and resolving fragmentation • Optimizing execution plan caching • Analyzing and avoiding statement recompilation • Minimizing blocking and deadlocks • Analyzing the effectiveness of cursor use • Applying in-memory table storage and procedure execution • Applying performance-tuning processes, tools, and optimization techniques to optimize SQL workloads www.it-ebooks.info Chapter ■ SQL Query Performance Tuning Before jumping straight into these topics, let’s first examine why we go about performance tuning the way we In this chapter, I discuss the basic concepts of performance tuning for a SQL Server database system It’s important to have a process you follow in order to be able to find and identify performance problems, fix those problems, and document the improvements you’ve made Without a well-structured process, you’re going to be stabbing in the dark, hoping to hit a target I detail the main performance bottlenecks and show just how important it is to design a database-friendly application, which is the consumer of the data, as well as how to optimize the database Specifically, I cover the following topics: • The performance tuning process • Performance versus price • The performance baseline • Where to focus efforts in tuning • The top 13 SQL Server performance killers What I don’t cover within these pages could fill a number of other books The focus of this book is on T-SQL query performance tuning, as the title says But, just so you’re clear, there will be no coverage of the following: • Hardware choices • Application coding methodologies • Server configuration (except where it impacts query tuning) • SQL Server Integration Services • SQL Server Analysis Services • SQL Server Reporting Services • PowerShell The Performance Tuning Process The performance tuning process consists of identifying performance bottlenecks, prioritizing the identified issues, troubleshooting their causes, applying different resolutions, and quantifying performance improvements—and then repeating the whole process again and again It is necessary to be a little creative, since most of the time there is no one silver bullet to improve performance The challenge is to narrow down the list of possible causes and evaluate the effects of different resolutions You can even undo previous modifications as you iterate through the tuning process The Core Process During the tuning process, you must examine various hardware and software factors that can affect the performance of a SQL Server–based application You should be asking yourself the following general questions during the performance analysis: • Is any other resource-intensive application running on the same server? • Is the capacity of the hardware subsystem capable of withstanding the maximum workload? • Is SQL Server configured properly? www.it-ebooks.info ■ Contents When to Use a Clustered Index�� 134 Poor Design Practices for a Clustered Index�� 135 Nonclustered Indexes��137 Nonclustered Index Maintenance�� 137 Defining the Lookup Operation�� 137 Nonclustered Index Recommendations�� 137 Clustered vs Nonclustered Indexes��138 Benefits of a Clustered Index over a Nonclustered Index�� 138 Benefits of a Nonclustered Index over a Clustered Index�� 141 Summary��142 ■■Chapter 9: Index Analysis��143 Advanced Indexing Techniques��143 Covering Indexes�� 144 A Pseudoclustered Index�� 145 Recommendations�� 145 Index Intersections�� 146 Index Joins�� 148 Filtered Indexes�� 150 Indexed Views�� 152 Index Compression�� 156 Columnstore Indexes�� 158 Special Index Types��161 Full-Text�� 161 Spatial�� 161 XML�� 161 Additional Characteristics of Indexes��162 Different Column Sort Order�� 162 Index on Computed Columns�� 162 Index on BIT Data Type Columns�� 162 CREATE INDEX Statement Processed As a Query�� 162 xi www.it-ebooks.info ■ Contents Parallel Index Creation�� 163 Online Index Creation�� 163 Considering the Database Engine Tuning Advisor�� 163 Summary��163 ■■Chapter 10: Database Engine Tuning Advisor��165 Database Engine Tuning Advisor Mechanisms��165 Database Engine Tuning Advisor Examples��170 Tuning a Query�� 170 Tuning a Trace Workload�� 175 Tuning from the Procedure Cache�� 178 Database Engine Tuning Advisor Limitations��179 Summary��180 ■■Chapter 11: Key Lookups and Solutions��181 Purpose of Lookups��181 Drawbacks of Lookups��183 Analyzing the Cause of a Lookup��184 Resolving Lookups��186 Using a Clustered Index�� 186 Using a Covering Index�� 186 Using an Index Join�� 190 Summary��192 ■■Chapter 12: Statistics, Data Distribution, and Cardinality��193 The Role of Statistics in Query Optimization��193 Statistics on an Indexed Column�� 194 Benefits of Updated Statistics�� 195 Drawbacks of Outdated Statistics�� 198 Statistics on a Nonindexed Column��200 Benefits of Statistics on a Nonindexed Column�� 200 Drawback of Missing Statistics on a Nonindexed Column�� 205 xii www.it-ebooks.info ■ Contents Analyzing Statistics��209 Density�� 212 Statistics on a Multicolumn Index�� 212 Statistics on a Filtered Index�� 214 Cardinality�� 216 Statistics Maintenance��219 Automatic Maintenance�� 219 Auto Create Statistics�� 220 Auto Update Statistics�� 220 Auto Update Statistics Asynchronously�� 222 Manual Maintenance�� 223 Manage Statistics Settings�� 224 Generate Statistics�� 225 Statistics Maintenance Status��225 Status of Auto Create Statistics�� 226 Status of Auto Update Statistics�� 226 Analyzing the Effectiveness of Statistics for a Query��226 Resolving a Missing Statistics Issue�� 227 Resolving an Outdated Statistics Issue�� 230 Recommendations��232 Backward Compatibility of Statistics�� 232 Auto Create Statistics�� 232 Auto Update Statistics�� 233 Automatic Update Statistics Asynchronously�� 235 Amount of Sampling to Collect Statistics�� 235 Summary��235 ■■Chapter 13: Index Fragmentation��237 Causes of Fragmentation��237 Page Split by an UPDATE Statement�� 239 Page Split by an INSERT Statement�� 244 xiii www.it-ebooks.info ■ Contents Fragmentation Overhead��245 Analyzing the Amount of Fragmentation��247 Analyzing the Fragmentation of a Small Table��250 Fragmentation Resolutions��252 Dropping and Re-creating the Index�� 252 Re-creating the Index with the DROP_EXISTING Clause�� 252 Executing the ALTER INDEX REBUILD Statement�� 253 Executing the ALTER INDEX REORGANIZE Statement�� 255 Defragmentation and Partitions�� 257 Significance of the Fill Factor��258 Automatic Maintenance��260 Summary��267 ■■Chapter 14: Execution Plan Generation��269 Execution Plan Generation��269 Parser�� 271 Binding�� 271 Optimization�� 273 Execution Plan Caching�� 280 Components of the Execution Plan��280 Query Plan�� 281 Execution Context�� 281 Aging of the Execution Plan��281 Summary��281 ■■Chapter 15: Execution Plan Cache Behavior��283 Analyzing the Execution Plan Cache��283 Execution Plan Reuse��284 Ad Hoc Workload��285 Prepared Workload�� 286 Plan Reusability of an Ad Hoc Workload�� 286 Plan Reusability of a Prepared Workload�� 294 xiv www.it-ebooks.info ■ Contents Query Plan Hash and Query Hash��303 Execution Plan Cache Recommendations��306 Explicitly Parameterize Variable Parts of a Query�� 306 Create Stored Procedures to Implement Business Functionality�� 306 Code with sp_executesql to Avoid Stored Procedure Maintenance�� 306 Implement the Prepare/Execute Model to Avoid Resending a Query String�� 307 Avoid Ad Hoc Queries�� 307 Prefer sp_executesql Over EXECUTE for Dynamic Queries�� 307 Parameterize Variable Parts of Queries with Care�� 308 Do Not Allow Implicit Resolution of Objects in Queries�� 308 Summary��309 ■■Chapter 16: Parameter Sniffing��311 Parameter Sniffing��311 Bad Parameter Sniffing�� 314 Mitigating Bad Parameter Sniffing�� 317 Summary��319 ■■Chapter 17: Query Recompilation��321 Benefits and Drawbacks of Recompilation��321 Identifying the Statement Causing Recompilation��324 Analyzing Causes of Recompilation��326 Schema or Bindings Changes�� 328 Statistics Changes�� 328 Deferred Object Resolution�� 331 SET Options Changes�� 335 Execution Plan Aging�� 336 Explicit Call to sp_recompile�� 336 Explicit Use of RECOMPILE�� 337 Avoiding Recompilations��340 Don’t Interleave DDL and DML Statements�� 340 Avoiding Recompilations Caused by Statistics Change�� 342 xv www.it-ebooks.info ■ Contents Using the KEEPFIXED PLAN Option�� 342 Disable Auto Update Statistics on the Table�� 344 Using Table Variables�� 344 Avoiding Changing SET Options Within a Stored Procedure�� 346 Using OPTIMIZE FOR Query Hint�� 347 Using Plan Guides�� 349 Summary��354 ■■Chapter 18: Query Design Analysis��355 Query Design Recommendations��355 Operating on Small Result Sets��356 Limit the Number of Columns in select_list�� 356 Use Highly Selective WHERE Clauses�� 357 Using Indexes Effectively��357 Avoid Nonsargable Search Conditions�� 358 Avoid Arithmetic Operators on the WHERE Clause Column�� 362 Avoid Functions on the WHERE Clause Column�� 364 Avoiding Optimizer Hints��366 JOIN Hint�� 367 INDEX Hints�� 370 Using Domain and Referential Integrity��372 NOT NULL Constraint�� 372 Declarative Referential Integrity�� 375 Summary��377 ■■Chapter 19: Reduce Query Resource Use��379 Avoiding Resource-Intensive Queries��379 Avoid Data Type Conversion�� 379 Use EXISTS over COUNT(*) to Verify Data Existence�� 382 Use UNION ALL Instead of UNION�� 383 Use Indexes for Aggregate and Sort Conditions�� 384 xvi www.it-ebooks.info ■ Contents Avoid Local Variables in a Batch Query�� 385 Be Careful When Naming Stored Procedures�� 389 Reducing the Number of Network Round-Trips��391 Execute Multiple Queries Together�� 391 Use SET NOCOUNT�� 392 Reducing the Transaction Cost��392 Reduce Logging Overhead�� 392 Reduce Lock Overhead�� 394 Summary��395 ■■Chapter 20: Blocking and Blocked Processes��397 Blocking Fundamentals��397 Understanding Blocking��398 Atomicity�� 398 Consistency�� 401 Isolation�� 401 Durability�� 402 Locks��403 Lock Granularity�� 403 Row-Level Lock�� 404 Page-Level Lock�� 406 Extent-Level Lock�� 406 Heap or B-tree Lock�� 407 Table-Level Lock�� 407 Database-Level Lock�� 407 Lock Operations and Modes��408 Lock Escalation�� 408 Lock Modes�� 408 Exclusive (X) Mode�� 413 Intent Shared (IS), Intent Exclusive (IX and Shared with Intent Exclusive (SIX) Modes�� 413 Schema Modification (Sch-M) and Schema Stability (Sch-S) Modes�� 414 xvii www.it-ebooks.info ■ Contents Bulk Update (BU) Mode�� 414 Key-range Mode�� 415 Lock Compatibility�� 415 Isolation Levels��415 Read Uncommitted�� 416 Read Committed�� 416 Repeatable Read�� 417 Serializable�� 420 Snapshot�� 425 Effect of Indexes on Locking��425 Effect of a Nonclustered Index�� 426 Effect of a Clustered Index�� 428 Effect of Indexes on the Serializable Isolation Level�� 429 Capturing Blocking Information��429 Capturing Blocking Information with SQL�� 430 Extended Events and the blocked_process_report Event�� 432 Blocking Resolutions��434 Optimize the Queries�� 435 Decrease the Isolation Level�� 435 Partition the Contended Data��436 Recommendations to Reduce Blocking��437 Automation to Detect and Collect Blocking Information��438 Summary��441 ■■Chapter 21: Causes and Solutions for Deadlocks��443 Deadlock Fundamentals��443 Choosing the Deadlock Victim�� 444 Using Error Handling to Catch a Deadlock�� 445 Deadlock Analysis��446 Collecting Deadlock Information�� 446 Analyzing the Deadlock�� 448 xviii www.it-ebooks.info ■ Contents Avoiding Deadlocks��455 Accessing Resources in the Same Physical Order�� 455 Decreasing the Number of Resources Accessed�� 456 Minimizing Lock Contention�� 456 Summary��458 ■■Chapter 22: Row-by-Row Processing��459 Cursor Fundamentals��459 Cursor Location�� 461 Cursor Concurrency�� 462 Cursor Types�� 463 Cursor Cost Comparison�� 466 Cost Comparison on Cursor Location�� 466 Cost Comparison on Cursor Concurrency�� 468 Read-Only�� 468 Cost Comparison on Cursor Type�� 469 Default Result Set��472 Benefits�� 472 Multiple Active Result Sets�� 472 Drawbacks�� 473 Cursor Overhead ��475 Analyzing Overhead with T-SQL Cursors�� 476 Cursor Recommendations�� 480 Summary��481 ■■Chapter 23: Memory-Optimized OLTP Tables and Procedures��483 In-Memory OLTP Fundamentals��483 System Requirements�� 484 Basic Setup�� 484 Create Tables�� 485 In-Memory Indexes�� 490 Hash Index�� 490 xix www.it-ebooks.info ■ Contents Natively Compiled Stored Procedures��495 Recommendations��497 Baselines�� 498 Correct Workload�� 498 Memory Optimization Advisor�� 498 Native Compilation Advisor�� 502 Summary��504 ■■Chapter 24: Database Performance Testing��505 Database Performance Testing��505 A Repeatable Process�� 506 Distributed Replay�� 506 Capturing Data with the Server-Side Trace��507 Distributed Replay for Database Testing��511 Configuring the Client�� 512 Running the Distributed Tests�� 512 Conclusion��513 ■■Chapter 25: Database Workload Optimization��515 Workload Optimization Fundamentals��515 Workload Optimization Steps�� 516 Sample Workload�� 517 Capturing the Workload��520 Analyzing the Workload��520 Identifying the Costliest Query��522 Determining the Baseline Resource Use of the Costliest Query�� 523 Overall Resource Use�� 524 Detailed Resource Use�� 524 Analyzing and Optimizing External Factors��526 Analyzing the Connection Options Used by the Application�� 527 Analyzing the Effectiveness of Statistics�� 527 xx www.it-ebooks.info ■ Contents Analyzing the Need for Defragmentation�� 528 Analyzing the Internal Behavior of the Costliest Query�� 532 Analyzing the Query Execution Plan�� 533 Identifying the Costly Steps in the Execution Plan�� 534 Analyzing the Processing Strategy�� 534 Optimizing the Costliest Query�� 535 Modifying the Code�� 535 Fixing the Key Lookup Operation�� 538 Tuning the Second Query�� 539 Creating a Wrapper Procedure�� 541 Analyzing the Effect on Database Workload��542 Iterating Through Optimization Phases��543 Summary��546 ■■Chapter 26: SQL Server Optimization Checklist��547 Database Design��547 Balancing Under- and Overnormalization�� 548 Benefiting from Entity-Integrity Constraints�� 549 Benefiting from Domain and Referential Integrity Constraints�� 551 Adopting Index-Design Best Practices�� 552 Avoiding the Use of the sp_ Prefix for Stored Procedure Names�� 554 Minimizing the Use of Triggers�� 554 Consider Putting Tables into In-Memory Storage�� 554 Configuration Settings��554 Memory Configuration Options�� 555 Cost Threshold for Parallelism�� 555 Max Degree of Parallelism�� 555 Optimize for Ad Hoc Workloads�� 555 Blocked Process Threshold�� 555 Database File Layout�� 556 Database Compression�� 556 xxi www.it-ebooks.info ■ Contents Database Administration��556 Keep the Statistics Up-to-Date�� 557 Maintain a Minimum Amount of Index Defragmentation�� 557 Avoid Database Functions Such As AUTO_CLOSE or AUTO_SHRINK�� 557 Database Backup��558 Incremental and Transaction Log Backup Frequency�� 558 Backup Scheduling Distribution�� 558 Backup Compression�� 559 Query Design��559 Use the Command SET NOCOUNT ON�� 560 Explicitly Define the Owner of an Object�� 560 Avoid Nonsargable Search Conditions�� 560 Avoid Arithmetic Expressions on the WHERE Clause Column�� 561 Avoid Optimizer Hints�� 561 Stay Away from Nesting Views�� 562 Ensure No Implicit Data Type Conversions�� 562 Minimize Logging Overhead�� 562 Adopt Best Practices for Reusing Execution Plans�� 562 Adopt Best Practices for Database Transactions�� 563 Eliminate or Reduce the Overhead of Database Cursors�� 564 Natively Compile Stored Procedures�� 564 Summary��564 Index��565 xxii www.it-ebooks.info About the Author Grant Fritchey, SQL Server MVP, works for Red Gate Software, a marketleading software-tools vendor, as its product evangelist He’s done development of large-scale applications in languages such as VB, C#, and Java, and he has worked in SQL Server since version 6.0 In addition, he has worked in insurance, finance, and consulting, as well as for three failed dot coms He is the author of SQL Server Execution Plans (Simple Talk Publishing, 2012) and SQL Server 2012 Query Performance Tuning (Apress, 2012) Grant is a coauthor of Beginning SQL Server 2012 Administration (Apress, 2012) and has one chapter in SQL Server MVP Deep Dives Volume (Manning, 2011) and Pro SQL Server 2012 Practices (Apress 2012) Grant travels and presents on various SQL Server topics at large conferences and small user groups around the world xxiii www.it-ebooks.info About the Technical Reviewer Joseph Sack (SackHQ.com) is an independent consultant based in Minneapolis, Minnesota With more than 17 years of experience in the industry, Joe is a consultant, author, speaker, SQL MVP, and SQL Server Microsoft Certified Master specializing in performance tuning, high availability, and disaster recovery His latest publication is the Microsoft white paper “Optimizing Your Query Plans with the SQL Server 2014 Cardinality Estimator.” xxv www.it-ebooks.info Acknowledgments I realize I might be repeating myself, but certain things bear repeating Book writing, hard Thank the gods I don’t have to this alone Jonathan Gennick of Apress tried to convince me that the book needed an update, but I talked him out of it Then we talked some more, and I realized he was right Thanks for your patience and trust taking me down this path again, Jonathan I found myself on my knees begging Joe Sack to be my tech editor again This is as much his book as it is mine Thanks for all your patient instruction, Joe As before, anything that’s wrong with this book is not from anything that you did Thanks While I don’t work there anymore, I learned so much at FM Global that I still need to give them credit for helping to build me, which helped to build this book Finally, thanks to the family for putting up with me going through this process again Special thanks to my wife Michele for her help with some of the graphics —Grant Fritchey xxvii www.it-ebooks.info ... where it impacts query tuning) • SQL Server Integration Services • SQL Server Analysis Services • SQL Server Reporting Services • PowerShell The Performance Tuning Process The performance tuning... in Chapter SQL Server Performance Killers Let’s now consider the major problem areas that can degrade SQL Server performance By being aware of the main performance killers in SQL Server in advance,... Chapter ■ SQL Query Performance Tuning Figure 1-1. Performance tuning process www.it-ebooks.info Chapter ■ SQL Query Performance Tuning You can see that the steps to optimize the costliest query

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