Persons on Events

[tiina303]

Related: https://github.com/PostHog/meta/issues/173

The primary goal of this issue is that PoE query mode (in terms of unique users) will return exactly the same results as joins with the person & distinct_id tables

To Do

• [x] Update squash workflow to utilize distinct ID overrides: #20329
• [x] Implement backfill: #20562, #20886
• [x] HogQL Support: #21059
• [ ] Feature flag for opting queries into v3 query path: #21150

Follow Up

Improvements

• [ ] Evaluate benefit of using a dictionary for override lookup: #20971
• [ ] Improve handling of deleted events when using overrides https://github.com/PostHog/posthog/pull/21059#issuecomment-2010696234
• [ ] Fix distinct_id reuse (possibly by tombstoning PG records) #20187

Clean Up

• [ ] Remove unused person overrides code and models/tables
• [ ] Revert #20659 to optimize squashes
• [ ] Additional considerations for self-hosted (backfilling, …)