Currently, when foreman search for a given parameter value, it would find the smart variable possible order and generate a few queries based on each matcher, for example:

SELECT "lookup_values".* FROM "lookup_values" WHERE "lookup_values"."match" = 'fqdn=host.example.com' AND ("lookup_values".lookup_key_id = 270) LIMIT 1
SELECT "lookup_values".* FROM "lookup_values" WHERE "lookup_values"."match" = 'domain=example.com' AND ("lookup_values".lookup_key_id = 270) LIMIT 1
SELECT "lookup_values".* FROM "lookup_values" WHERE "lookup_values"."match" = 'os=redhat 6.2' AND ("lookup_values".lookup_key_id = 270) LIMIT 1
.
.
.

since this happens for every parameter, this could eventually slow the system down.
an alternative approch would be to query to all possible values in one go, for example

 LookupValue Load (0.2ms)  SELECT "lookup_values".* FROM "lookup_values" WHERE "lookup_values"."match" = 'domain=example.com' AND "lookup_values"."lookup_key_id" IN (376, 270, 377, 275, 261)