8 Replies Latest reply on Jan 9, 2014 12:31 AM by Martin H.

    Query speeds when using "custom SQL" vs datavase view vs native tableau data source

    Martin H.

      Hi there,

       

      I read all over the net how bad custom SQL is when used as a data source because Tableau cannot write the most efficient queries when it is used. I have tested report performance using Tableau's performance recording feature to verify that, I had the same star schema created the conventional Tableau way, then based a database view on the same star, third data source was custom SQL using the exact SQL code as the view and finally extract. Needless to say extract outperforms by a factor the other options, but my observations are that

       

      * Custom SQL and VIEW based data sources performed comparable

      * The classical data source, the view based source and the custom SQL data source gave me similar run times the first time  I ran them

      * Custom SQL and VIEW based data sources ran about ~20% faster after the initial run, probably caching kicks in but I am not sure if that happens on Tableau's side or database side as it receives basically the exact same SQL request

      * the classical data source kept running at the same (slow) times every run, as if no caching occurred

       

      Has anyone performed real life tests to support the statement that custom SQL is bad?

      Thanks