Creation of user_ids

[ACPK]

The site makes use of the preview salt in order to generate user_ids.

For data scientists that are trying to understand the raw data, would it be possible to get a quick description on how user_ids are generated?

previous_user_id = salts[:previous] && generate_user_id(conn, params, salts[:previous])
event = struct(Plausible.ClickhouseEvent, event_attrs)
session_id = Plausible.Session.Store.on_event(event, previous_user_id)

[ukutaht]

Sure, you can find an explanation here: https://plausible.io/data-policy#how-we-count-unique-users-without-cookies

[ACPK]

@ukutaht - Thank you for the quick reply and hope your year is off to a great start! I had read the post but am still confused.

The post mentions "Old salts are deleted to avoid the possibility of linking visitor information from one day to the next."

Is the previous salt not an old salt (i.e., salts[:previous])) and being used to link visitor information from one day to the next?

[ukutaht]

We keep the latest 2 salts around so that session data doesn't get broken at midnight abritrarily. When salts are rotated, the salts[:previous] part ensures that active sessions are carried over and not split in half. Old salts are deleted once they have served their purpose meaning within 48 hours of their creation.