For a SQL Server database set at compatibility level 120 and above, the legacy cardinality estimator (CE version 70) can be activated at the database level by using theALTER DATABASE SCOPED CONFIGURATION. SQL ALTERDATABASESCOPED CONFIGURATIONSETLEGACY_CARDINALITY_ESTIMATION =ON; GOSELECTname,valu...
For a SQL Server database set at compatibility level 120 and above, the legacy cardinality estimator (CE version 70) can be activated at the database level by using theALTER DATABASE SCOPED CONFIGURATION. SQL ALTERDATABASESCOPED CONFIGURATIONSETLEGACY_CARDINALITY_ESTIMATION =ON; GOSELECTname,value...
可以参考”SQL Server中关于基数估计如何计算预估行数的一些探讨“或官方文档Optimizing Your Query Plans with the SQL Server 2014 Cardinality Estimator 如果谓词很简单,如“CustomerID=11142”,并且搜索值恰好是直方图RANGE_HI_KEY(直方图梯级的上限列值端),则EQ_ROWS可用于非常准确的估计基数。如下所示: USEAdventu...
参考资料 https://docs.microsoft.com/en-us/sql/relational-databases/performance/cardinality-estimation-sql-server?view=sql-server-2017 https://blogs.msdn.microsoft.com/psssql/2015/06/16/identifying-sql-server-2014-new-cardinality-estimator-issues-and-service-pack-1-improvement/...
优化器有很多方式估算基数的算法,我们这里列举几种简单的方式,如果你想了解更多基数估计的算法。可以参考”SQL Server中关于基数估计如何计算预估行数的一些探讨“或官方文档Optimizing Your Query Plans with the SQL Server 2014 Cardinality Estimator 如果谓词很简单,如“CustomerID=11142”,并且搜索值恰好是直方图RANGE...
Prior to SQL Server 2014, cardinality estimator was largely based on SQL Server 7.0 code base. SQL Server 2014 introduces new design and the new cardinality estimator is based on research on modern workloads and learning from past experience. A whitepaper planned by the SQL Server product tea...
This paper provides an overview of the primary changes made to the cardinality estimator functionality by the Microsoft query processor team, covering how to enable and disable the new cardinality estimator behavior, and showing how to troubleshoot plan-quality regressions if and when they occur....
You can read more about CE changes in the white paperOptimizing Your Query Plans with the SQL Server 2014 Cardinality Estimator. For correlated columns in the 2014 CE, to derive cardinality we need to sort the filters according to their density, where the smallest density v...
Knowing that the CE has changed and purposefully was not overcautiously re-architected to avoid regressions, you need to prepare a little more carefully for a SQL Server 2014 upgrade if you will utilize the new Cardinality Estimator. Based on our experience so far, you...
Assume that you have enabledthe new cardinality estimatorin Microsoft SQL Server 2014. When you run a query that contains join statements, you may encounter the following issues: Some queries take significantly longer time to compile, especial...