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    Editing Raw Reflections

    You can edit an existing raw reflection. You might want to do so if you are iteratively designing and testing a raw reflection, if the definition of the view that the reflection was created from was changed, or if the schema of the underlying table was changed.

    If you created a raw reflection in the Basic view of the reflections editor, you must use the Advanced view to edit it.

    Procedure

    1. Open the reflections editor.
      See “Locations of the Reflections Editor” to find out where you can open the editor from.
    2. Click the Advanced View button in the top-right corner of the editor.
    3. In the Raw Reflections section of the Advanced view, locate the table that shows the definition of your reflection.
    4. (Optional) Click in the label to rename the reflection.
      The purpose of the name is to help you understand, when you read job reports, which reflections the query optimizer considered and chose when planning queries.
    5. In the columns of the table, follow these steps, which you don’t have to do in any particular order:

      Note:
      Ignore the Distribution column. Selecting fields in it has no effect on the reflection.

    • Click in the Display column to include fields in or exclude them from your reflection.
    • Click in the Sort column to select fields on which to sort the data in the reflection. For guidance in selecting a field on which to sort, see the section “Sort Reflections on High-Cardinality Fields” in “Best Practices for Creating Raw and Aggregation Reflections”.
    • Click in the Partition column to select fields on which to horizontally partition the rows in the reflection. For guidance in selecting fields on which to partition, see the section “Horizontally Partition Reflections that Have Many Rows”.

    1. (Optional) Optimize the number of files used to store the reflection. You can optimize for fast refreshes or for fast read performance by queries.

      If the underlying tables for your reflection are set to Incremental Refresh, then changing the setting of this option affects only new data that is added to your reflection at each refresh.

      If the underlying tables are set to Full Refresh, then changing the setting of this option affects the entire set of data in the reflection. The new setting takes effect at the next full refresh.

      Follow these steps:

      a. Click the gear icon in the table in which you are defining the reflection.

      b. In the field Reflection execution strategy, select either of these options:

      • Options
        • Select Minimize Time Needed To Refresh if you need the reflection to be created as fast as possible. This option can result in the data for the reflection being stored in many small files. This is the default option.
        • Select Minimize Number Of Files when you want to improve read performance of queries against the reflection. With this option, there tend to be fewer seeks performed for a given query.

    2. Click Save when you are finished.

    Result

    Dremio runs the job or jobs to recreate the reflection.