In a recent post, I discussed issues I found when testing the Machine Learning Services setup in SQL Server 2017.
After that, my old friend Niels Berglund also posted about issues he found after installing CU7 (cumulative update 7) and how he solved them. Niels' article is here: http://www.nielsberglund.com/2018/06/01/sql-server-machine-learning-services-and-sql-server-2017-cu-7/
What each of those articles discussed though was detail on how temporary files are used by Machine Learning Services in SQL Server to hold R or Python data for sessions. By default, SQL Server configures itself to hold data for up to 20 concurrent sessions.
You can change that number.
In SQL Server Configuration Manager, find the LaunchPad service:
In the Properties page for the service, select the Advanced tab. In the main image above, you can see the value that you can change to increase the number of concurrent sessions.
Values up to 100 are permitted.
SQL Server also creates passwords for these "external" users. If you have a policy that requires regular password changes, you'll see that there's also an option in this window to let you change all of them.
(It's worth noting that current NIST guidelines say that you shouldn't force regular password updates anyway – you'll find more info here: https://auth0.com/blog/dont-pass-on-the-new-nist-password-guidelines/)