Fixes #5395: added note about session table id column length

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>
 

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}}';