How do I enable caching across requests/actions?

My stack:

* Rails 4.2.7
* Postgres 9.5

I notice the following in my Rails logs

```
  Country Load (0.4ms)  SELECT  "countries".* FROM "countries" WHERE "countries"."iso" = $1 LIMIT 1  [["iso", "US"]]
  State Load (1.4ms)  SELECT  "states".* FROM "states" WHERE "states"."iso" = $1 AND "states"."country_id" = $2 LIMIT 1  [["iso", "OH"], ["country_id", 233]]
  Country Load (0.3ms)  SELECT  "countries".* FROM "countries" WHERE "countries"."iso" = $1 LIMIT 1  [["iso", "US"]]
  State Load (1.1ms)  SELECT  "states".* FROM "states" WHERE "states"."iso" = $1 AND "states"."country_id" = $2 LIMIT 1  [["iso", "OH"], ["country_id", 233]]
  Country Load (3.6ms)  SELECT  "countries".* FROM "countries" WHERE "countries"."iso" = $1 LIMIT 1  [["iso", "US"]]
  State Load (1.2ms)  SELECT  "states".* FROM "states" WHERE "states"."iso" = $1 AND "states"."country_id" = $2 LIMIT 1  [["iso", "OH"], ["country_id", 233]]

```

Note that the same queries are being run multiple times against my database in rapid succession. Is there some way I can indicate to Rails that certain tables/models are very unlikely to change, and so certain lookups can be cached on the app server?