Set exit_page only on pageviews

[macobo]

Changes

Previously we set and updated exit_page on all events, which can cause issues when:

1. Sessions without any pageviews are made (e.g. user leaves a tab open and returns to it)
2. It results in exit_page exit_rate calculations returning numbers above 100

Additional context under https://3.basecamp.com/5308029/buckets/35611491/card_tables/cards/7162713530

Tests

• Automated tests have been added
• This PR does not require tests

Changelog

• Entry has been added to changelog
• This PR does not make a user-facing change

[zoldar]

The change makes sense to me, but it seems to also require updating how we query for stats so that we filter out custom events-only sessions from breakdowns/aggregates in which they do not apply. That might have some wider implications too, but I'm not familiar enough with that aspect to tell for sure 😅 Probably best if @ukutaht has a closer look at this too.

[aerosol]

Would be good to look into those test failures. Can't quickly tell if it's a fixture error, a regression or if there's something easily abused with the way we populate test data.

[macobo]

Test failures were real - we were creating Signup events in the relevant tests.

Given that this also affects bounce rates, etc as per these example tests, it would be great to have @ukutaht's input before merging this.

but it seems to also require updating how we query for stats so that we filter out custom events-only sessions from breakdowns/aggregates in which they do not apply

@zoldar I'm considering that a separate task that's slightly trickier than this given the wide-reaching ramifications. I was planning to make sure this gets a satisfying solution, but is less urgent than this fix. If you have input/thoughts or want to lead that feel free! 🙇

[ukutaht]

For extra clarity I think this test could also assert that session.entry_page == ""

[macobo]

This brings up a question: Should we also update entry_page on a subsequent event if a) it's a pageview and b) session doesn't have entry_page set?

After re-visiting I think we should set exit_page to /path/2 here as well, thoughts?

[ukutaht]

After re-visiting I think we should set exit_page to /path/2 here as well, thoughts?

you mean entry_page rather than exit_page, right?

Yeah I think that does make sense. Then entry page and exit page will always correspond to the first and last pageview in a session which feels intuitive to me.

[ukutaht]

Wait, I approved too early. Why does this affect bounce rates? 👀

[ukutaht]

As per discsussion, this solution is good. Let's do it!