Hi All,I'm testing out SQL 2014 migrated from our current Prod backup of SQL 2008 R2 database.I'm aware of the MDOP setting, however when troubleshooting a poor performing query, I'm at a loss for reason.Our Sql 2014 server (latest cu) has 4 cores with MDOP set to 2. Stats and compatibility updated. When investigating a query, said query by default runs "really slow /abnormal". (17 minutes)I checked the query plan and it's cost is about 500, and runs in parallel as expected.I tested the set OPTION (QUERYTRACEON 9481) to prevent SQL 2014 from using the new Cardinality Estimator(CE). The query ran as fast / "normal like SQL 2008". It's cost was about 500.In checking the plan, it does use MaxDOP 2. (53 seconds)Then then I tested query with OPTION MAXDOP 1 not using the Trace 9481, it runs fastest with cost about 600 (43 seconds)Query is running a large Data Warehouse report, so I expect a lot of reads.Any clues as to why this behaviour changes so dramatically with MDOP of 1. (I'm ruling out reverting to the old CE when we eventually upgrade to SQL 2014 to Production.Thank you in advance.-RR
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