diff --git a/docs/guide/runtime-sessions-cookies.md b/docs/guide/runtime-sessions-cookies.md
index eda136f7a1..d0d28d9208 100644
--- a/docs/guide/runtime-sessions-cookies.md
+++ b/docs/guide/runtime-sessions-cookies.md
@@ -174,7 +174,7 @@ where 'BLOB' refers to the BLOB-type of your preferred DBMS. Below are the BLOB
 - PostgreSQL: BYTEA
 - MSSQL: BLOB
 
-
+Note that length of id column should be adjusted if `session.hash_function` is changed in `php.ini`.
 
 ### Flash Data <a name="flash-data"></a>
 
diff --git a/framework/web/DbSession.php b/framework/web/DbSession.php
index 96fa8b2df6..e4bd7ff836 100644
--- a/framework/web/DbSession.php
+++ b/framework/web/DbSession.php
@@ -65,6 +65,8 @@ class DbSession extends Session
      *
      * When using DbSession in a production server, we recommend you create a DB index for the 'expire'
      * column in the session table to improve the performance.
+     *
+     * Note that length of id column should be adjusted if `session.hash_function` is changed in `php.ini`.
      */
     public $sessionTable = '{{%session}}';