BQ export from GA4 rollup appears to retain sessionIDs from the source properties

[DorcasAatCAT]

When pulling data from BigQuery for a linked GA4 rollup property, the sessionID appears to be retained from the GA4 source property. We infer this because the sessionID varies as a user proceeds from one hostname to another hostname.

The same user data has only a single sessionID in the BigQuery data for a linked UA rollup property - the sessionID never varies across all the different hostnames. This enabled us to pull UA data easily by sessionID.

Unfortunately pulling similar data in GA4 is now extremely cumbersome and requires a complex workaround. For some scenarios we anticipate there may not be any feasible workaround.

Will GA4 be providing a consolidated sessionID dimension (possibly named something else) for export to BigQuery in the future?

We would expect there to be a consolidated sessionID for rollup properties, either replacing the source property sessionID when exported to BigQuery, or populating a unique new rollupSessionID dimension when exported to BigQuery.

[jaia]

Hello,

Thank you for contacting Google Cloud Community!

The behavior you've described with session IDs in GA4 linked properties is expected. In GA4, session IDs are scoped to the source property level. This means that when a user moves from one hostname to another within the same GA4 property, a new session is created, and a new session ID is assigned.
However, in UA, session IDs are scoped to the domain level. So, even if a user moves from one hostname to another within the same domain, the same session ID is maintained. This is why you're seeing a single session ID for UA data across different hostnames.
You could create a custom dimension in your GA4 properties to track a consolidated session ID. This would require implementing custom JavaScript code to track user behavior and set the custom dimension's value.

Regards,
Jai Ade

[DorcasAatCAT]

It sounds like you're saying what used to be done for us in UA rollup properties, i.e. setting a consolidated session ID, is no longer available in GA4 rollup properties.

I'm not sure what "scoped at the domain level" has to do with anything though, because we see the same consolidated session ID across different domains in UA rollup property data. There was no session ID in UA source properties; it appeared to be something Google created during the processing of source property data into the UA rollup property. 

Thanks anyway for confirming that Google has decided not to maintain that process, and will not create a consolidated session ID in GA4 rollup properties.

On the other hand, it doesn't sound feasible to create a custom dimension for consolidated session ID in GA4 source properties. We already have both the client ID and the user ID in our data, but the consolidating doesn't happen until the data is merged in the rollup, and we can't using JavaScript to insert data into the rollup property - we only link the source properties and then Google does (or does not) do the rest.