[3.2.x] Added note about culling in database cache backend docs.

Co-authored-by: Mariusz Felisiak <felisiak.mariusz@gmail.com>

Backport of 6e155d280dbe4bab171619654d8abc4b7f197e78 from main

1 files changed, 4 insertions, 0 deletions

diff --git a/docs/topics/cache.txt b/docs/topics/cache.txt
index 477a43d298..cb254a71a7 100644
--- a/docs/topics/cache.txt
+++ b/docs/topics/cache.txt
@@ -195,6 +195,10 @@ In this example, the cache table's name is ``my_cache_table``::
         }
     }
 
+Unlike other cache backends, the database cache does not support automatic
+culling of expired entries at the database level. Instead, expired cache
+entries are culled each time ``add()``, ``set()``, or ``touch()`` is called.
+
 Creating the cache table
 ~~~~~~~~~~~~~~~~~~~~~~~~