원본 링크 : http://searchsqlserver.techtarget.com/feature/Trace-flags

Skip Startup Stored Procedures (4022) : 시작 프로시져를 스킵

This is a handy trace flag for troubleshooting. It forces SQL Server to skip startup stored procedures. This is especially useful if a stored procedure has been altered and causes harm to your system. After you set this trace flag, you can then debug the stored procedure and set it back to its original state.

Ignore All Index Hints (8602) 모든 인덱스 힌트를 무시 

Trace flag 8602 is a commonly used trace flag to ignore index hints that are specified in a query or stored procedure. This is a fantastic option when you're trying to determine if an index hint is hurting more than helping. Rather than rewriting the query, you can disable the hint using this trace flag and rerun the query to determine if SQL Server is handling the index selection better than the index hint.

Disable Locking Hints (8755) 락 힌트를 비활성화

Trace flag 8755 will disable any locking hints like READONLY. By setting this, you allow SQL Server to dynamically select the best locking hint for the query. If you feel the query's locking hint may be hurting performance, you can disable it and rerun the query.

Disable All Other Hints (8722) 모든 힌트를 비활성화

Lastly, the 8722 trace flag will disable all other types of hints. This includes the OPTION clause.

원본 링크  : http://www.sqlservergeeks.com/blogs/AmitBansal/sql-server-bi/663/sql-server-did-you-know-about-trace-flag-4136

So what about Trace Flag 4136 ? 

(Microsoft SQL Server 2008 R2 Cumulative Update 2, SQL Server 2008 Service Pack 1 (SP1) Cumulative Update 7 and Microsoft SQL Server 2005 Service Pack 3 (SP3) Cumulative Update 9 introduce trace flag 4136)

While OPTIMIZE FOR UNKNOWN disables parameter sniffing at query level, trace flag 4136 disables parameter sniffing at instance level. Which means, no parameter sniffing for that instance – all queries/workloads for all databases get affected with this.

trace 8649
http://connect.microsoft.com/SQLServer/feedback/details/714968/provide-a-hint-to-force-generation-of-a-parallel-plan