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Docs: Speeding up facets with indexes

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Simon Willison 2018-05-16 21:08:50 -07:00
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docs/facets.rst
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@ -118,3 +118,13 @@ For the currently filtered data are there any columns which, if applied as a fac
* And the query used to evaluate this criteria can be completed in under 20ms
That last point is particularly important: Datasette runs a query for every column that is displayed on a page, which could get expensive - so to avoid slow load times it sets a time limit of just 20ms for each of those queries. This means suggested facets are unlikely to appear for tables with millions of records in them.
Speeding up facets with indexes
-------------------------------
The performance of facets can be greatly improved by adding indexes on the columns you wish to facet by. Adding indexes can be performed using the ``sqlite3`` command-line utility. Here's how to add an index on the ``state`` column in a table called ``Food_Trucks``::
$ sqlite3 mydatabase.db
SQLite version 3.19.3 2017-06-27 16:48:08
Enter ".help" for usage hints.
sqlite> CREATE INDEX Food_Trucks_state ON Food_Trucks("state");