skip column cache in unusual cases

just in case we're trying to log a redis error. blowing the stack
isn't cool

Change-Id: I396584bc45f36089f2219ee5215745fcf6444ddc
Reviewed-on: https://gerrit.instructure.com/160951
Tested-by: Jenkins
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>

config/initializers/postgresql_adapter.rb

@@ -261,8 +261,21 @@ module PostgreSQLAdapterExtensions
   end
 
   def column_definitions(table_name)
-    MultiCache.fetch(["schema", table_name]) do
+    return super if @nested_column_definitions
+    @nested_column_definitions = true
+    begin
+      got_inside = false
+      MultiCache.fetch(["schema", table_name]) do
+        got_inside = true
+        super
+      end
+    rescue
+      raise if got_inside
+      # we never got inside, so something is wrong with the cache,
+      # just ignore it
       super
+    ensure
+      @nested_column_definitions = false
     end
   end
 end