Troubleshooting SQL Server Performance: Tips &Tools

Amit Khandelwal

DISCLAIMER

The opinions expressed in this presentation and on the following slides are solely those of the presenter and not necessarily those of Microsoft. Microsoft does not guarantee the accuracy or reliability of the information provided herein.

About me:

I am currently working as Microsoft SQL Server Support Escalation Engineer. Worked with Beta Teams for SQL Server release and masters SQL Performance, HR-DR technologies and Replication and Engine technologies. Have Authored several internal training materials. Have been speaker at many programs like SQL Server Talks, SQL Server Asia level conference and many others. Current interests in learning and working on SQL Server Azure and other cloud products of Microsoft.

Agenda

Performance Troubleshooting ToolsSQLDIAG\PSSDIAGSQL Nexus

SQL Nexus Analysis Waits analysisCPU\Spinlocks

Old School Tricks!!!

Slow I\O Troubleshooting

Common Mysteries & Important Trace flags

PERFORMANCE TROUBLESHOOTING TOOLS

SQLDIAG\PSSDIAGSQL Nexus

SQLDIAG– Data collection utility

Windows Event Logs (Application, System, and Security) in .CSV filesSystem Monitor (aka Perfmon) performance counters in .BLG file/s

SQL Server Profiler traces in .TRC file/sSQL Server error logs, configuration, point-in-time snapshots of several DMVs in a .OUT file

System information via the Msinfo32 utilityCustom scripts for collecting blocking specific data All configuration parameters are stored in SQLDiag.xml file and can be changed

PSSDIAG – Data collection utility

Similar to SQLDIAG utility except for the user interface

• CPU spikes on the SQL Server box• Performance degradation during specific hours (say

between 4:00 PM and 6:00 PM daily)• Blocking on SQL Server• Overall performance bottlenecks in SQL Server using

wait statistics

SQL Nexus – Data analysis tool

Helpful in post-mortem analysis of performance issuesUses RML utilities (Readtrace) – It’s a pre-requisite

Tool Highlights:Trace aggregation to show TOP N most expensive queriesWait stats analysis for visualizing blocking and other resource contention issuesVisualize loaded data via Reports – uses SSRS client side report viewer

PSSDIAG and SQL Nexus:Nexus analyses data when SQLDiag is clubbed with SQLxxxxPerfStats scriptSQLxxxxPerfStats scripts captures DMVs output including blocking information

PSSDIAG AND SQL NEXUS DEMO

SLOW I\O TROUBLESHOOTING

I/O Troubleshooting

2015-28-08 00:00:00.00 spid1 SQL Server has encountered 192 occurrence(s) of IO requests taking longer than 15 seconds to complete on file [E:\SQLServer\Testdb.mdf] in database [Testdb] (7). The OS file handle is 0x00000000000074D4. The offset of the latest long IO is: 0x00000000022000.

The message indicates that SQL Server has been waiting on at least one I/O for 15 seconds or longer

This represents Stuck\Stalled IO requests on SQL Server

I/O TroubleshootingTools and Techniques

• Performance Monitor Counters (Perfmon)

PhysicalDisk\Avg. Disk

sec/Transfer

(<0.015)

PhysicalDisk\Avg. Disk

Queue Length(<2 per spindle)

PhysicalDisk\% Idle Time

(~100%)

PhysicalDisk\Disk Bytes/sec

Process\IO Data Bytes/sec(sqlservr)

sys.dm_io_pending_io_requestsLook out for “io_pending” column of this DMV. The io_pending column indicates 1 if the I/O is still pending within the kernel.

COMMON MYSTERIES

Common Mysteries

SQL Server is using high CPU, but PSSDIAG does not show CPU getting accounted to the queries running in SQL Server!!!

How does Rebuild\reorg indexes affect statistics?

SQL Server consumes all the memory that I give!!

What is minimum Server memory? Can SQL take more than Max server memory?

IMPORTANT TIPS

Important Trace Flags

T4199 This trace flag is a combination of a lot of optimizer related fixes released under different trace flags.

T1236 Enable this trace flag when you see elevated values occur for LOCK_HASH spinlock count

T1117 This trace flag applies to the entire SQL Server instance, not just to one DB, and it affects all files in the same file group in a database.

T1118 This trace flag forces uniform extent allocations instead of mixed page allocations. The trace flag is commonly used to assist in TEMPDB scalability by avoiding SGAM and other allocation contention points

T8048 This trace flag will upgrade NODE based partitioning to CPU based partitioning.

Power plan setting*

Max Degree of Parallelism

Max Server Memory

Client Side Tracing

Missing Indexes DMV &

Database Tuning Advisor

Upgrade SQL to latest Hotfixes\

SPs

ReferencesPSSDIAGhttp://diagmanager.codeplex.com/releases http://technet.microsoft.com/en-us/library/ms162833.aspxhttp://blogs.msdn.com/b/pamitt/archive/2011/02/25/how-to-use-the-sqldiag-the-sqlnexus-and-the-pal-tools-to-analyze-performance-issues-in-sql-server.aspx

SQL Nexushttp://sqlnexus.codeplex.com/ https://sqlnexus.codeplex.com/wikipage?title=GETTING_STARTED http://sqlnexus.codeplex.com/wikipage?title=Sql2005PerfStatsScript&referringTitle=Home https://sqlnexus.codeplex.com/wikipage?title=collecting%20data%20using%20batch%20files&referringTitle=GETTING_STARTED http://sqlnexus.codeplex.com/wikipage?title=readtrace&referringTitle=Sql2005PerfStatsScript

Slow I\O Troubleshooting http://support.microsoft.com/kb/897284 http://blogs.msdn.com/b/karthick_pk/archive/2012/06/26/io_2d00_bottlenecks.aspx http://blogs.msdn.com/b/cindygross/archive/2010/03/17/what-do-those-io-requests-taking-longer-than-15-seconds-messages-on-my-sql-box-mean.aspx

References

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