diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index d3e5b0a4adbc1a6a5ea99d88e834b85e098bf8d1..6310d7019279ca34fa2fea054beea6dca2727fdc 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -431,22 +431,16 @@ def translate_exception(exception, message)
       private
 
         def get_oid_type(oid, fmod, column_name, sql_type = '') # :nodoc:
-
-          result = type_map.fetch(oid, fmod, sql_type) {
-            nil
-          }
-
-          unless result
+          if !type_map.key?(oid)
             load_additional_types(type_map, [oid])
-            result = type_map.fetch(oid, fmod, sql_type) {
-              warn "unknown OID #{oid}: failed to recognize type of '#{column_name}'. It will be treated as String."
-              Type::Value.new.tap do |cast_type|
-                type_map.register_type(oid, cast_type)
-              end
-            }
           end
 
-          result
+          type_map.fetch(oid, fmod, sql_type) {
+            warn "unknown OID #{oid}: failed to recognize type of '#{column_name}'. It will be treated as String."
+            Type::Value.new.tap do |cast_type|
+              type_map.register_type(oid, cast_type)
+            end
+          }
         end
 
         def initialize_type_map(m) # :nodoc:
diff --git a/activerecord/lib/active_record/type/hash_lookup_type_map.rb b/activerecord/lib/active_record/type/hash_lookup_type_map.rb
index 2a146d38a9d87b77e5d2fd78fed961f9a73ed53b..bf92680268fcabe8f832168f38d9bff58d538128 100644
--- a/activerecord/lib/active_record/type/hash_lookup_type_map.rb
+++ b/activerecord/lib/active_record/type/hash_lookup_type_map.rb
@@ -1,12 +1,6 @@
 module ActiveRecord
   module Type
     class HashLookupTypeMap < TypeMap # :nodoc:
-
-      def initialize
-        @cache = {}
-        super
-      end
-
       delegate :key?, to: :@mapping
 
       def lookup(type, *args)
@@ -14,24 +8,12 @@ def lookup(type, *args)
       end
 
       def fetch(type, *args, &block)
-        cache = (@cache[type] ||= {})
-        resolved = cache[args]
-
-        unless resolved
-          resolved = cache[args] = @mapping.fetch(type, block).call(type, *args)
-        end
-
-        resolved
+        @mapping.fetch(type, block).call(type, *args)
       end
 
       def alias_type(type, alias_type)
         register_type(type) { |_, *args| lookup(alias_type, *args) }
       end
-
-      def register_type(key, value=nil, &block)
-        @cache = {}
-        super(key, value, &block)
-      end
     end
   end
 end