When capturing events, Snowplow offers several out of the box fields to help you identify and track sessions and users.
user_id
This identifier is a manually configured identifier set by your logic when initialising the Snowplow tracker. It's included as a default field for all events and can be used for user stitching across services and domains.
domain_userid
This stores a field value taken from the first-party cookie set by the tracker.
domain_sessionid
This stores a field value taken from the first-party cookie. The domain session is generated by the tracker when a user first visits the website.
domain_sessionidx
This field relates to the domain_sessionid by capturing the number of times a user triggers an event after the expiry of the previous session (by default 30 minutes). By combining domain_sessionid with domain_sessionidx we can see how many distinct sessions the user has had.
network_userid
This stores a field value taken from the first-party cookie set by the collector.