Route lookup optimization database calls

In https://gitlab.com/gitlab-com/gl-infra/infrastructure/snippets/1875425 the following two SQL queries account for more than 13% of all queries executed on GitLab.com:

SELECT "routes".\* FROM "routes"   
WHERE "routes"."source_id" = ?   
AND "routes"."source_type" = ?   
LIMIT ? 

SELECT "projects".\* FROM "projects"   
INNER JOIN "routes" ON "routes"."source_id"   
= "projects"."id" AND "routes"."source_type"   
= ? WHERE ((LOWER(routes.path)   
= LOWER(?))) ORDER BY (CASE WHEN   
routes.path = ? THEN ? ELSE ?   
END) LIMIT ?

Considering how much time we spend in these queries, is there more that we could do to optimize them or cache their results?

cc @abrandl