We have online production database which is running in SQL Server 2008 R2. Now we are planning to migrate to SQL Server 2014.We notice SQL querys were performing very slow in SQL 2014 comparing SQL 2008 while testing performance in same hardware configuration.When we change compatibility to 100 in SQL 2014(i.e SQL 2008 mode),then it uses old execution plan(i.e sql 2008) and executes faster.But our requirement is to set latest compatibility mode to 120 and ensure improved or at least same performance as that of SQL 2008.I also tried by enabling trace flag 9481 works fine but it goes off after SQL server restartBut i heard there is cardinality estimator option in SQL 2016 which will support legacy versions to generate the execution plans of querys as like in older verions but it is not in SQL 2014.So ps advise .
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