Add Guides note to change cache name space as Entry data is incompatible between 3.2 and 4.0

1 files changed, 4 insertions, 0 deletions

diff --git a/guides/source/upgrading_ruby_on_rails.md b/guides/source/upgrading_ruby_on_rails.md
index 4ce61c282d..a3cccf5215 100644
--- a/guides/source/upgrading_ruby_on_rails.md
+++ b/guides/source/upgrading_ruby_on_rails.md
@@ -915,6 +915,10 @@ Also check your environment settings for `config.action_dispatch.best_standards_
 
 Rails 4.0 removes the `j` alias for `ERB::Util#json_escape` since `j` is already used for `ActionView::Helpers::JavaScriptHelper#escape_javascript`.
 
+#### Cache
+
+The caching method changed between Rails 3.x and 4.0. You should [change the cache namespace](http://guides.rubyonrails.org/caching_with_rails.html#activesupport-cache-store) and roll out with a cold cache.
+
 ### Helpers Loading Order
 
 The order in which helpers from more than one directory are loaded has changed in Rails 4.0. Previously, they were gathered and then sorted alphabetically. After upgrading to Rails 4.0, helpers will preserve the order of loaded directories and will be sorted alphabetically only within each directory. Unless you explicitly use the `helpers_path` parameter, this change will only impact the way of loading helpers from engines. If you rely on the ordering, you should check if correct methods are available after upgrade. If you would like to change the order in which engines are loaded, you can use `config.railties_order=` method.