In order to populate suggestions for filters in Explore or in dashboards, Looker issues a
SELECT DISTINCT query when you first start typing to select all distinct values of a specific field. As you continue typing, previous queries are cancelled before a new query is issued.
SELECT DISTINCT items.name FROM items WHERE items.name LIKE 'j%'
would be cancelled in favor of:
SELECT DISTINCT items.name FROM items WHERE items.name LIKE 'jacke%'
A new query is only issued after 300 milliseconds pass without any new typing (so if you type a letter every 200ms, no new query will be issued).
After any of these
DISTINCT queries finishes, no more queries are issued as you continue typing. Instead, Looker’s front end eliminates non-matching values without hitting the database.