SQL Server 2008性能故障排查（一）——概論

原文: SQL Server 2008性能故障排查（一）——概論

備註：本人花了大量下班時間翻譯，絕無抄襲，容許轉載，但請註明出處。因爲篇幅長，沒法一篇博文所有說完，同時也沒那麼快所有翻譯完，因此按章節發佈。因爲本人水平有限，翻譯結果確定存在問題，爲了避免形成誤導，在每篇結尾處都附上原文，供你們參考，也但願能指出個人問題，以便改進。謝謝。

另外，本文寫給稍微有經驗的數據庫開發人員或者DBA看，初學者可能會看不懂。在此請見諒

做者：Sunil Agarwal, Boris Baryshnikov, KeithElmore, Juergen Thomas, Kun Cheng, Burzin Patel

技術評審：Jerome Halmans, Fabricio Voznika,George Reynya

發佈於：2009年3月

適用於：SQL Server 2008

概要：

有時候對一個工做負載進行劣質的數據庫設計或者不正確的系統配置會引發SQLServer運行緩慢。DBA須要主動地防止或者最小化問題，而且當問題發生後，診斷問題的原由並做出正確的響應。本文提供逐步指引，使用公開可用的工具如 SQLServer Profiler、性能監視器、DMV、SQLServer擴充事件和 數據收集器來診斷和排查常見性能問題。

 

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簡介：

SQLServer偶爾運行緩慢是不常見的現象。通常緣由能夠歸結爲：對一個工做負載進行劣質的數據庫設計或者不正確的系統配置。做爲一個DBA，須要主動避免或者最小化問題。當問題發生時，須要去診斷原由和做出正確的對策。本白皮書提供了各類工具如SQLServer Profiler、性能監視器、DMV、SQLServer擴充事件和數據收集器來診斷和排查常見性能問題。本白皮書把問題範圍限制在一些客戶常常反映的地方，由於分析全部可能的問題是不現實的。

目標：

本文的主要目的是提供常規方法，主要是一些公開的、可用的工具用於診斷和故障排查。SQLServer 2008在支持性上有了重大的提高。添加了一些新動態管理視圖（DMV）：如sys.dm_os_memory_brokers,sys.dm_os_memory_nodes,sys.dm_exec_procedure_stats。已有（2005出現）的DMV好比：sys.dm_os_sys_info,sys.dm_exec_requests和sys.dm_exec_requests也添加了不少新的信息。你能夠DMV和使用現有的工具如SQL Server Profiler、性能監視器來收集性能相關數據用於分析。
第二個目的是介紹新的故障排查工具和2008特性，包括擴充事件(Extended Events)和數據收集器(data collector)

方法論：

SQLServer運行緩慢的緣由可能有不少種，本文中根據下面3個主要症狀來開始問題診斷：

•  資源瓶頸（Resource Bottlenecks）：CPU、內存和I/O瓶頸都將在本文中說起。咱們不考慮網絡問題。在每一個資源瓶頸中，咱們會描述如何標識出問題而後迭代地檢查可能的緣由。好比，一個內存瓶頸會引發過多的頁面切換從而影響性能。
• TempDB瓶頸：由於在每一個SQLServer實例中，只有一個tempdb可被個個數據庫使用，因此它可能成爲性能問題和硬盤空間瓶頸。一個應用可能由於過多的DDL或者DML操做，而且耗用過多資源，會使得tempdb超負荷。這能引發非相關的、運行在同一服務器上的應用程序變得緩慢甚至運行失敗。
• 一個運行緩慢的用戶查詢：一個已存在的查詢可能會影響性能，或者一個新的查詢會耗費比想象中更多的資源。通常由如下緣由引發：

  一、一個現有查詢的統計信息的改變會使得優化器選擇一個性能低下的執行計劃。
  二、丟失索引將致使強制表掃描和減慢查詢速度。
  三、應用程序也會由於阻塞從而影響性能，即便資源利用狀況很正常。
  四、一些很差的應用程序、不合理的架構設計或者使用了不合適的事務隔離級別，都會致使過多的阻塞。
上面的這些緣由不該該分開來分析，低效的執行計劃會加劇系統資源的使用從而引發工做負載的性能整體降低。因此，若是一個大表丟失了一個有效的索引，或者查詢優化器不選擇使用這個索引，那麼查詢將很是慢。這些狀況也同時會對I/O子系統的讀操做帶來很大壓力，由於不得不去讀取一些原本不必或者原本已經緩存在內存中的頁。相似於一個常常運行的程序過分的編譯將爲CPU帶來壓力。

•  在SQL Server 2008中新的性能工具：SQLServer2008提供了新的工具和特性去協助你監控和故障排查。咱們主要討論的是：擴充事件和數據收集器

資源瓶頸（Resource Bottlenecks）：

在接下來的部分，將討論CPU、內存和I/O子系統資源，而且討論在什麼狀況下它們會成爲瓶頸（網絡部分不在本文討論範圍內）。對於每一個資源瓶頸，咱們將討論如何識別問他你，而後迭代地檢查可能的緣由。好比內存瓶頸將致使切換頁面過多，從而影響性能。
在你能判斷性能瓶頸以前，你必須知道在正常狀況下資源是如何被利用的。你能使用本文描述的方法去收集性能基線。即在沒有性能問題以前的性能數據。
你可能發現資源使用正常，可是SQLServer在目前的配置下不能支持相應的負載。爲了解決這個問題，你可能不得不增長更多更強大的資源，如內存、加大你目前I/O或者網絡的帶寬。可是，在你執行以前，你有必要先了解資源瓶頸的常規原由。一些解決方案，如從新配置，而不必定非要增長資源。

解決資源瓶頸的工具：

下列工具中的一個或多個能在解決部分性能問題時使用到：
 性能監視器（Performance Monitor）：在部分Windows 操做系統中提供，詳細的瞭解請查閱Windows文檔。
 SQLServer Profiler：在SQLServer的性能工具組中能夠找到，能夠查看聯機叢書瞭解。
 DBCC命令：能夠查看附錄A和聯機叢書瞭解。
 DMVs：詳細可查看聯機叢書。
 擴充事件（Extended Events）：能夠查看稍後提到的Extended Events部分和聯機叢書。
 數據收集器和管理數據倉庫（Data collector and the management data warehouse(MDW)）：能夠查看稍後說起的Data collector and MDW部分及聯機叢書。

下一節：CPU瓶頸

原文：

Troubleshooting Performance Problems in SQL Server 2008 SQL Server Technical Article Writers: Sunil Agarwal, Boris Baryshnikov, Keith Elmore, Juergen Thomas, Kun Cheng, Burzin Patel Technical Reviewers: Jerome Halmans, Fabricio Voznika, George Reynya Published: March 2009 Applies to: SQL Server 2008 Summary: Sometimes a poorly designed database or a system that is improperly configured for the workload can cause the slowdowns in SQL Server. Administrators need to proactively prevent or minimize problems and, when they occur, diagnose the cause and take corrective action. This paper provides step-by-step guidelines for diagnosing and troubleshooting common performance problems by using publicly available tools such as SQL Server Profiler, Performance Monitor, dynamic management views, and SQL Server Extended Events (Extended Events) and the data collector, which are new in SQL Server 2008. Copyright The information contained in this document represents the current view of Microsoft Corporation on the issues discussed as of the date of publication. 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 presented after the date of publication. This white paper is for informational purposes only. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED, OR STATUTORY, AS TO THE INFORMATION IN THIS DOCUMENT. Complying with all applicable copyright laws is the responsibility of the user. Without limiting the rights under copyright, no part of this document may be reproduced, stored in, or introduced into a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), or for any purpose, without the express written permission of Microsoft Corporation. Microsoft may have patents, patent applications, trademarks, copyrights, or other intellectual property rights covering subject matter in this document. Except as expressly provided in any written license agreement from Microsoft, the furnishing of this document does not give you any license to these patents, trademarks, copyrights, or other intellectual property. Unless otherwise noted, the example companies, organizations, products, domain names, e-mail addresses, logos, people, places, and events depicted herein are fictitious, and no association with any real company, organization, product, domain name, e-mail address, logo, person, place, or event is intended or should be inferred. © 2009 Microsoft Corporation. All rights reserved. Microsoft, MSDN, SQL Server, Win32, Windows, Windows Server, and Windows Vista are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries. All other trademarks are property of their respective owners.   Table of Contents Introduction 1 Goals 1 Methodology 1 Resource Bottlenecks 2 Tools for Resolving Resource Bottlenecks 2 CPU Bottlenecks 3 Excessive Query Compilation and Optimization 4 Detection 5 Resolution 7 Unnecessary Recompilation 9 Detection 10 Resolution 13 Inefficient Query Plan 14 Detection 15 Resolution 15 Intraquery Parallelism 16 Detection 18 Resolution 21 Poor Cursor Usage 21 Detection 22 Resolution 23 Memory Bottlenecks 23 Background 23 Virtual Address Space and Physical Memory 23 AWE, Locked Pages, and SQL Server 23 Memory Pressures 25 Detecting Memory Pressures 26 Tools for Memory Diagnostics 26 New DMVs in SQL Server 2008 27 Resource Governor in SQL Server 2008 27 External Physical Memory Pressure 28 External Virtual Memory Pressure 30 Internal Physical Memory Pressure 30 Caches and Memory Pressure 36 Ring Buffers 37 Internal Virtual Memory Pressure 43 General Troubleshooting Steps in Case of Memory Errors 44 Memory Errors 44 I/O Bottlenecks 48 Resolution 52 tempdb 56 Monitoring tempdb Space 58 Troubleshooting Space Issues 59 User Objects 59 Version Store 60 Internal Objects 62 Excessive DDL and Allocation Operations 65 Resolution 66 Slow-Running Queries 66 Blocking 67 Locking Granularity and Lock Escalation 69 Identifying Long Blocks 71 Blocking per Object with sys.dm_db_index_operational_stats 74 Overall Performance Effect of Blocking Using Waits 75 Monitoring Index Usage 78 Extended Events 80 Data Collector and the MDW 88 Appendix A: DBCC MEMORYSTATUS Description 95 Appendix B: MDW Data Collection 96 Introduction It’s not uncommon to experience the occasional slowdown of a database running the Microsoft® SQL Server® database software. The reasons can range from a poorly designed database to a system that is improperly configured for the workload. As an administrator, you want to proactively prevent or minimize problems; if they occur, you want to diagnose the cause and take corrective actions to fix the problem whenever possible. This white paper provides step-by-step guidelines for diagnosing and troubleshooting common performance problems by using publicly available tools such as SQL Server Profiler; System Monitor (in the Windows Server® 2003 operating system) or Performance Monitor (in the Windows Vista® operating system and Windows Server 2008), also known as Perfmon; dynamic management views (sometimes referred to as DMVs); and SQL Server Extended Events (Extended Events) and the data collector, which are new in SQL Server 2008. We have limited the scope of this white paper to the problems commonly seen by Microsoft Customer Service and Support, because an exhaustive analysis of all possible problems is not feasible. Goals The primary goal of this paper is to provide a general methodology for diagnosing and troubleshooting SQL Server performance problems in common customer scenarios by using publicly available tools. SQL Server 2008 has made great strides in supportability. New dynamic management views (DMVs) have been added, like sys.dm_os_memory_brokers, sys.dm_os_memory_nodes, and sys.dm_exec_procedure_stats. Existing DMVs such as sys._dm_os_sys_info, sys.dm_exec_requests, and sys.dm_exec_requests have been enriched with additional information. You can use DMVs and existing tools, like SQL Server Profiler and Performance Monitor, to collect performance related data for analysis. The secondary goal of this paper is to introduce new troubleshooting tools and features in SQL Server 2008, including Extended Events and the data collector. Methodology There can be many reasons for a slowdown in SQL Server. We use the following three key symptoms to start diagnosing problems: • Resource bottlenecks: CPU, memory, and I/O bottlenecks are covered in this paper. We do not consider network issues. For each resource bottleneck, we describe how to identify the problem and then iterate through the possible causes. For example, a memory bottleneck can lead to excessive paging that ultimately impacts performance. • tempdb bottlenecks: Because there is only one tempdb for each SQL Server instance, it can be a performance and a disk space bottleneck. An application can overload tempdb through excessive DDL or DML operations and by taking too much space. This can cause unrelated applications running on the server to slow down or fail. • A slow-running user query: The performance of an existing query might regress, or a new query might appear to be taking longer than expected. There can be many reasons for this. For example: o Changes in statistical information can lead to a poor query plan for an existing query. o Missing indexes can force table scans and slow down the query. o An application can slow down due to blocking even if resource utilization is normal. o Excessive blocking can be due to poor application or schema design or the choice of an improper isolation level for the transaction. The causes of these symptoms are not necessarily independent of each other. The poor choice of a query plan can tax system resources and cause an overall slowdown of the workload. So, if a large table is missing a useful index, or if the query optimizer decides not to use it, the query can slow down; these conditions also put heavy pressure on the I/O subsystem to read the unnecessary data pages and on the memory (buffer pool) to store these pages in the cache. Similarly, excessive recompilation of a frequently-run query can put pressure on the CPU. New Performance Tools in SQL Server 2008 SQL Server 2008 introduced new features and tools that you can use to monitor and troubleshoot performance problems. We’ll discuss two features: Extended Events and the data collector. Resource Bottlenecks The next sections of this paper discuss CPU, memory, and I/O subsystem resources and how these can become bottlenecks. (Network issues are outside of the scope of this paper.) For each resource bottleneck, we describe how to identify the problem and then iterate through the possible causes. For example, a memory bottleneck can lead to excessive paging, which can ultimately impact performance. Before you can determine whether you have a resource bottleneck, you need to know how resources are used under normal circumstances. You can use the methods outlined in this paper to collect baseline information about the use of the resource (at a time when you are not having performance problems). You might find that the problem is a resource that is running near capacity and that SQL Server cannot support the workload in its current configuration. To address this issue, you may need to add more processing power or memory, or you may need to increase the bandwidth of your I/O or network channel. However, before you take that step, it is useful to understand some common causes of resource bottlenecks. Some solutions, such as reconfiguration, do not require the addition of more resources. Tools for Resolving Resource Bottlenecks One or more of the following tools can be used to resolve a particular resource bottleneck: • Performance Monitor: This tool is available as part of the Windows® operating system. For more information, see your Windows documentation. • SQL Server Profiler: See SQL Server Profiler in the Performance Tools group in the SQL Server 2008 program group. For more information, see SQL Server 2008 Books Online. • DBCC commands: For more information, see SQL Server 2008 Books Online and Appendix A. • DMVs: For more information, see SQL Server 2008 Books Online. • Extended Events: For more information, see Extended Events later in this paper and SQL Server 2008 Books Online. • Data collector and the management data warehouse (MDW): For more information, see Data Collector and the MDW later in this paper and SQL Server 2008 Books Online.