2016-04-08 11:44:28 -04:00
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FAQ
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===
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Can I query/join multiple tables at one time?
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---------------------------------------------
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Not directly no. A Caravel SQLAlchemy datasource can only be a single table
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or a view.
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When working with tables, the solution would be to materialize
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a table that contains all the fields needed for your analysis, most likely
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through some scheduled batch process.
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A view is a simple logical layer that abstract an arbitrary SQL queries as
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a virtual table. This can allow you to join and union multiple tables, and
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to apply some transformation using arbitrary SQL expressions. The limitation
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there is your database performance as Caravel effectively will run a query
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on top of your query (view). A good practice may be to limit yourself to
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joining your main large table to one or many small tables only, and avoid
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using ``GROUP BY`` where possible as Caravel will do its own ``GROUP BY`` and
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doing the work twice might slow down performance.
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Whether you use a table or a view, the important factor is whether your
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database is fast enough to serve it in an interactive fashion to provide
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a good user experience in Caravel.
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How BIG can my data source be?
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------------------------------
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It can be gigantic! As mentioned above, the main criteria is whether your
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database can execute queries and return results in a time frame that is
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acceptable to your users. Many distributed databases out there can execute
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queries that scan through terabytes in an interactive fashion.
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2016-06-30 20:33:51 -04:00
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How do I create my own visualization?
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-------------------------------------
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We are planning on making it easier to add new visualizations to the
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framework, in the meantime, we've tagged a few pull requests as
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``example`` to give people examples of how to contribute new
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visualizations.
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https://github.com/airbnb/caravel/issues?q=label%3Aexample+is%3Aclosed
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2016-07-22 13:25:23 -04:00
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Why are my queries timing out?
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------------------------------
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If you are seeing timeouts (504 Gateway Time-out) when running queries,
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it's because the web server is timing out web requests. If you want to
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increase the default (50), you can specify the timeout when starting the
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web server with the ``-t`` flag, which is expressed in seconds.
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``caravel runserver -t 300``
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