Why you should not increase the max length of the User ID field [sys_user.user_name] which is limited to 40 characters Out of the BoxSummaryThe User ID is a unique identifier for the user's ServiceNow login user name. The maximum length of the User ID field in the User [sys_user] table is 40, which means the User ID in the User table can only have 40 or fewer characters: So if you enter/update a User ID manually, the platform will not allow you to enter more than 40 characters. Also, if you create/update a user in other ways than manually (via an integration, XML upload, etc.) and provide a User ID that has more than 40 characters, only the first 40 characters will be kept and saved. You may have a requirement to have User IDs with more than 40 characters and the platform would allow you to increase the Max Length of the [sys_user.user_name] field. However, we advised not to increase the max length of the User ID field because it might create issues. While some of the issues caused by changing this value have been addressed over the years, the fact is that the platform has not been designed to handle User IDs with more than 40 characters. What else is dependent on the User ID field? The User ID is used to populate the Created by and Updated by fields. These 2 read-only fields are automatically added to every table that is being created (except if the table extends another one as the 2 fields from the parent will be used). The max length of these 2 fields is 40. What are the issues which can arise by increasing the max length of the user ID field? The User IDs will be truncated to 40 characters when they are stored in the Created by and Updated by fields. This can lead to seeing values that look the same if the first 40 characters of different User IDs happen to be the same. That can raise various issues such as:* Confusion among users* Reports and filters returning incorrect results* Failing ACLs* Flow Designer flow getting stuck when the Run As field is set to 'User who initiates session'* etc.Users with a User ID longer than 40 characters will also not be able to attach files to a record.