![]() ![]() Before switching modes, it's important to determine whether the advantages of query execution on the backend server outweigh any reduction in functionality. Tabular models in DirectQuery mode have some limitations. If the model contains complex formulas that might require multiple queries, Analysis Services can perform optimization to ensure that the query plan for the query executed against the back-end database will be as efficient as possible. Security can be enforced by the back-end source database by using row-level security features from the database (alternatively, you can use row-level security rules defined in the model by using DAX). Changes to the underlying source data can be immediately reflected in queries against the data model.ĭatasets can be larger than the memory capacity of an Analysis Services server resource.ĭirectQuery can take advantage of provider-side query acceleration, such as that provided by memory-optimized column indexes. No processing (refresh) of model data is required. There is no extra management overhead of having to maintain a separate copy of the data (in the in-memory cache). ![]() Because data is always queried at the data source, client reporting applications are always getting the latest data. However, there are some limitations to using cached data, for example, very large data sets can exceed available memory and processing (refresh) of in-memory model data can require excessive amounts of available resources if needed frequently.ĭirectQuery overcomes these limitations while also leveraging RDBMS features making query execution more efficient. When tabular models query data residing in-memory, even complex queries can be very fast. Benefitsīy default, tabular models use an in-memory cache to store and query data. Before choosing DirectQuery mode, it's important to understand both the benefits and limitations. DirectQuery mode can be enabled for models you're designing in Visual Studio, or for tabular models that have already been deployed, you can change to DirectQuery mode by using SQL Server Management Studio (SSMS). This article describes DirectQuery mode for Analysis Services tabular models at the 1200 and higher compatibility levels. ![]()
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