implementation of table columns that won't explode in large collections

src/metabase/driver/mongo.clj

@@ -24,9 +24,10 @@
   [table]
   (with-mongo-connection [^com.mongodb.DBApiLayer conn @(:db table)]
     (->> (mc/find-maps conn (:name table))
-         (r/map keys)
-         (r/map set)
-         (r/reduce set/union))))
+         (take 10000)                      ; it's probably enough to only consider the first 10,000 docs in the collection instead of iterating over potentially millions of them
+         (map keys)
+         (map set)
+         (reduce set/union))))
 
 (defn- field->base-type
   "Determine the base type of FIELD in the most ghetto way possible, via `values->base-type`."