This presentation briefly explains how to use a trace flag and highlights 12 more common trace flags in SQL Server. Some trace flags are specific to SQL Server 2012 or 2014.

1. 12 Trace Flags
In 12-ish Minutes
Matt Slocum

2. Matt Slocum – Who am I?
 DBA manager with a passion for SQL Server
 Experience with SQL Server v6.5-2014
 Specialize in replication and performance tuning
 MCITP: DBA SQL 2005 & 2008
 MCSE: SQL 2012 Data Platform
 Leader of Rochester PASS SSUG
 Established SQL Saturday Rochester
 5th annual event was in May 2016
11/17/201612 Trace Flags in 12-ish Minutes2 |

3. How To Use Trace Flags
 Ad-hoc Enable
 DBCC TRACEON (####, -1)
 #### = Trace Flag
 -1 (optional) = Server vs. Query level
 Ad-hoc Disable
 DBCC TRACEOFF (####, -1)
 Status
 DBCC TRACESTATUS
 Startup Parameter - SQL Server Configuration Manager
 -T####
 Query option
 OPTION (QUERYTRACEON ####)
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4. High IO Databases (TempDB & User)
 TF 1117 (Server level)
 Grow all data files on a database when one data file
needs to grow
 Keeps data files consistently sized
 Use: On all instances that have DBs with > 1 data file
 TF 1118 (Server level)
 Reserve an entire Extent in the data cache when one
new page is allocated
 Reduces overhead of allocating additional pages
 Use: On every instance everywhere
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5. SQL 2014/2016 Cardinality Estimator
 TF 9481 (Server or Session/Query level)
 Use emulated SQL 2012 Cardinality Estimator
 Use: SQL 2014 plans are not as optimal as 2012
 TF 2312 (Session/Query level)
 Forces SQL 2014 Native Cardinality Estimator
 Only need to use when 9481 is set at the server level
 Use: When 9481 is set on the server and you have
queries that perform better with the SQL 2014 CE
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6. Statistics Auto Updates/Estimations
 TF 2371 (Server level)
 Reduce percentage of change required before
automatically updating statistics on large tables
 Use: Everywhere (SQL 2008 R2+)
 TF 2389/2390 (Server level)
 Affects statistics on ascending columns
 Query optimizer will query the highest value from the
column so that it can create accurate estimates
 Use: When you experience bad estimates when
querying columns with ascending values
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7. Tune Query Plan Generation
 TF 6498 (Server level)
 Enables multiple simultaneous large query
compilations in SQL 2014
 Use: SQL 2014 when you experience this wait:
RESOURCE_SEMAPHORE_QUERY_COMPILE
 TF 4136 (Server or Session/Query level)
 Disables parameter sniffing
 Causes reduced performance on skewed datasets
 Use: Query level preferred when parameter sniffing
causes poor performance.
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8. Optimize CPU utilization
 TF 8008 (Server level)
 Cause the scheduler to evaluate which NUMA/soft-
NUMA node to execute a query on
 Prevents one CPU/NUMA node from running hot
while the others are much less utilized
 Use: If you see CPU contention on one NUMA node
 TF 8048 (Server level)
 Optimizes how the scheduler assigns work to NUMA
nodes with > 8 logical CPUs.
 SQL 2008 - 2014 SP1 (soft-NUMA in 2014 SP2)
 Use: Run queries in MS article to determine if needed
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9. Suppress Successful Backup Logs
 TF 3226
 Successful backups are not logged to the
ERRORLOG
 Keeps your ERRORLOG cleaner
 Use: All instances of SQL Server
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10. Conclusion
 Test, test, TEST
 Official MS recommendations
 https://support.microsoft.com/en-us/kb/2964518
 Do your homework and see what works
 If you don’t need it, don’t use it
 SQL 2016 enables a lot automatically:
 https://www.brentozar.com/archive/2016/03/sq
l-server-2016-death-trace-flag/
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11. Thank you!
 Blog: www.sqlmatt.com
 Twitter: @SlocumMatt
 Rochester PASS Website:
http://rochesterpass.sqlpass.org/
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