Queries are automatically generated every time you add a field to a shelf and interact with the view. Tableau offers several ways you can manage these queries once they are sent to the underlying data source.
- Automatic Updates
- Cancel Query
- Abandoned Queries
- Precision Warnings
When you place a field on a shelf, Tableau generates the view by querying the data source.
If you are creating a dense data view that involves many fields, the queries might be time consuming and significantly degrade system performance. In this case, you can instruct Tableau to turn off automatic updates.
By default, automatic updates are turned on and the toolbar button is highlighted . However, it is sometimes more efficient for Tableau to execute the queries you need for your final view, rather than for every intermediate step required to compose that view. You can turn off updates by pressing F10 or the Automatic Updates toolbar button .
While automatic updates are turned off, you can still update the view at any time by clicking F9 or the Run Update on the toolbar. This way, you can update your data view at an intermediate step. It is possible to enter an invalid state when automatic updates are turned off. When this happens, the view is desaturated and invalid commands are disabled. The view and commands become available again when you click Run Update on the toolbar.
For example, the view below has automatic updates turned off. When the aggregation for Profit is changed from a summation to an average, the view is desaturated to let you know that you have made a change to the view that has made the current view invalid.
This command is used any time you want to stop a query that is in process. You may want to cancel a query that is taking a long time to complete due to the size of the data source. When a query is taking a long time to complete, a progress dialog box opens. You can cancel a requested query by clicking the Cancel button on the Processing Request dialog box.
When you cancel a query in Tableau, the database is told to stop processing the query. However, some databases do not support cancel (MS Excel, MS Access, Essbase, Microsoft Analysis Services 2000). If you cancel a query using one of these types of data sources, the query is abandoned by Tableau but is still running in the background and using resources. When you have abandoned queries, an indicator appears in the bottom right corner of the workbook showing the number of queries still running . As queries in the background complete, the number will go down. It is important to monitor the number of queries running and not let the number get too high, otherwise you will see performance degradation of both Tableau and the underlying database.
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When you add a field to a view that contains values with more precision than Tableau can model, a warning icon is displayed in the bottom right corner of the status bar. For example, a value in the database may have 22 decimal places but Tableau only supports up to 15. When you add that field to the view, you get a precision warning. If you click on the warning, you can read more details including the number of decimal places that have been truncated in the view.
Remember that the precision of the data displayed in Tableau will always first be dependent on the data in your database. If the values in your database exceed 15 decimal places, when you add them to the view, the value is truncated and a precision warning appears.
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