R1:ee1e2da8fbf4

Avoid Timeline race condition

Summary: While I should fix the transactional stuff, that patch is going to be
tricky and transactions have some performance implications. This is a simple
fix which prevents the race.

Instead of having the data point at the event ID, have the event point at a
data ID. Insert the data first, then insert the event with the right data
pointer. This is super simple and prevents the race issue.

Test Plan:
- Ran the schema upgrade script, verified that the database was…