1. SQL SERVER CONFIGURATION OPTIONS AND TRACE FLAG SECRETS Kevin Kline SQL Sentry, Director of Engineering Services @KEKline on Twitter, FB, LI Blogs at http://KevinEKline.com and http://ForITPros.comhttp://KevinEKline.comhttp://ForITPros.com

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3. AGENDA SP_Configure o Red Herrings o DBoptions Trace Flags o The general details about trace flags Resources & Wrap up

4. SP_CONFIGURE SETTINGS Min and Max SQL Server Memory Special considerations for Windows “Lock Pages in Memory” Optimize for Ad hoc Workloads Fill Factor at 70-80% for OLTP applications Parallelism is not the boogyman: o No kneejerk reactions – thinking about disabling MaxDOP (set to 1)? o May prefer Cost Threshold for Parallelism, especially for OLTP applications Bottom-line Behavior

5. SP_CONFIGURE RED HERRINGS Boost SQL Server Priority Max Worker Threads Lightweight Pooling CPU Affinity Locks Query Wait Query Cost Governor Limit Don’t Use These Unless Testing Proves Otherwise

6. SURPRISING DATABASE OPTIONS Parameterization: o Simple or Forced o For experienced DBAs only Database Read-Only o Can help with locking o Specialize! Compatibility Levels o Might not do what you think it does…

7. WHAT ARE TRACE FLAGS? A directive used to “set specific server characteristics or to enable/disable a particular behavior” Enabled at different scopes and contexts: o Scopes are Global or Session. o Contexts are Startup or Query. Documentation sources: o Expected sourcs: BOL, KB articles / Service Pack & Cumulative Update o Unexpected: readme files, white papers, blogs / user groups / “water cooler” CAVEATS! No legal action complaining if something goes wrong!

8. USING TRACE FLAGS IN T-SQL DBCC { TRACEON | TRACEOFF | TRACESTATUS } o Use -1 to enable a trace flag globally o Add -T to the SQLServer startup command to enable startup global trace flag Within a query using OPTION (QUERYTRACE n) Sometime trace flags seem to do “nothing”. To see their output: o DBCC TRACEON (3604): Send output to console o DBCC TRACEON (3605): Send output to ERRORLOG

9. T F’ING–A! SAFE* IN PRODUCTION T610 speeds up high volume data loads by writing less information to the transaction log for minimally logged inserts into indexed tables. T834 enables SQL Server, on 64-bit systems, to use large-page allocations for the buffer pool. T835 enables “lock pages in memory” for Std Ed

10. -T1118: BLESSED BY ZEUS Tells SQL Server to allocate full extents to each tempdb objects, rather than mixed extents. o Less contention on internal structures such as SGAM pages o Story has improved in subsequent releases of SQL Server o So represents a “edge case” ZEUS =

11. T F’ING DEADLOCKS T1204 writes information about deadlocks to the ERRORLOG in a “text format”. T1222 writes information about deadlocks to the ERRORLOG in a “XML format” o Resources o Types of locks Duration of deadlocks are affected by enabling this trace flag.

12. T F’ING UP LOCKS T1200 returns locking information in real-time as your query executes o Use during development / testing phase o Great for learning how SQL Server implements locking T1211 disables lock escalation based on memory pressure or number of locks. T1224 disables lock escalation until 40% of memory is used and then re- enables escalation o When enabled, MSSQL won’t escalate row or page locks to table locks. o T1211 takes precedence over T1224 o Microsoft recommends using T1224 Trace flag 1211 prevents escalation in every case, even under memory pressure and may help avoid "out-of-locks" errors when many locks are being used. Warning! Can generate excessive number of locks, can slow performance, even cause 1204 errors.

13. T F’ING PARALLELIZED OPERATIONS T2528 disables parallel checking of objects during DBCC CHECKDB, CHECKFILEGROUP and CHECKTABLE. o Default leaves parallel DBCC checks enabled. DBCC operations can dynamically change their degree of parallelism. T2562 perform the entire set of checks in a single ‘batch’ instead of multiple batches, and increase the efficient of per-thread calls to get a new list of pages to read. T2549 treats each database file as if it’s on a separate physical drive for the purposes of driving read-ahead for DBCC CHECKDB o Alternatives: MAXDOP option Resource Governor

14. T F’ING DATA CONSISTENCY T806 enables DBCC audit checks to be performed on pages to test for logical consistency problems. o These checks try to detect when a read operation from a disk does not experience any errors but the read operation returns data that is not valid. o Pages will be audited every time that they are read from disk. o Affects performance! This should only be used in systems where data stability is in question.

15. T F’ING UP THE DATABASE FILES T3004 returns more information about instant file initialization (IFI). Useful to see if SQL Server has been configured to take advantage of IFI correctly. Not often used T1117 tells SQL Server autogrow all files in a database at the same time

16. T F’ING UP THE TRANSACTION LOG T3422 enables log record auditing to troubleshoot log file corruption o Careful! It introduces overhead to each transaction log record write. o Similarly to trace flag 806, you would only use this to troubleshoot corruption problems

17. T F’ING UP CHECKPOINTS T3502 enables detailed tracking of CHECKPOINTs to the ERRORLOG T3505 disables automatic checkpoints: o Setting trace flag 3505 may increase recovery time and can prevent log space reuse until the next checkpoint is issued. o Make sure to issue manual checkpoints on all read/write databases at appropriate time intervals Microsoft recommends that you do not change the recovery interval because it may affect data safety and availability.

18. T F’ING UP BACKGROUND PROCESSES T661 disables the ghost record cleanup process. T8020 disables working set monitoring T2330 disables all index usage stats gathering T2371 enables proportional automatic update statistics T2389 and T2390 enables auto-quick-statistics update for ascending keys, whether known or unknown, respectively

19. T F’ING UP THE RING BUFFERS T818 enables the ring buffer for tracking the last 2,048 successful write operations, not including sort and workfile I/Os. T8011 disables the ring buffer for Resource Monitor T8012 disables the ring buffer for schedulers T8018 disables exception ring buffer T8019 disables stack collections for the exception ring buffer

20. T F’ING UP THE OPTIMIZER T652 disables page pre-fetching scans T4199 enables all fixes that were previously made for the query processor under many trace flags/hot fixes based on “special” policy T2301 enables advanced optimizations specific for BI and processing very large data sets T2312 and T9481 enables or disables the new SQL2014 cardinality estimator, respectively T2861 enables caching trivial plans T8744 disables pre-fetching ranges for nested loop operations.

21. T F’ING DEBUGGING QUERIES The slide notes contain an exhaustive list of all query debugging trace flags that I’m aware of. Many are undocumented. Use at your own risk. First, always enable T3604. T8615: Shows the final memo structure. o Look for the ‘Good Enough Plan Found’ message T8675: Shows optimization stages and times. o Simplification stage = trivial plan o Search (0 … n) = transactional, quick, and full plans

22. DEMO

23. A TRACE FLAG I ALWAYS WISHED FOR… T8780 allows you to “turn off” query optimizer time outs. o Don’t use without plenty of testing. o Allows optimizer differentiate between the optimal plan and the best plan. o My recommendation: Consider using only on batches that are used bazillions of times per day.

24. RESOURCES Best blogs: o http://sqlskills.com/blogs/paul http://sqlskills.com/blogs/paul o http://sqlperformance.com, especially Paul White’s query tuning posts http://sqlperformance.com o http://www.somewheresomehow.ru/optimizer_unleashed_1/, a good blog in Russian about advanced query tuning http://www.somewheresomehow.ru/optimizer_unleashed_1/ Trace Flags: http://www.victorisakov.comhttp://www.victorisakov.com 24

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