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# Problem Timeline creation can either be bootstrap or branch. The distinction is made based on whether the `ancestor_*` fields are present or not. In the PGDATA import code (https://github.com/neondatabase/neon/pull/9218), I add a third variant to timeline creation. # Solution The above pushed me to refactor the code in Pageserver to distinguish the different creation requests through enum variants. There is no externally observable effect from this change. On the implementation level, a notable change is that the acquisition of the `TimelineCreationGuard` happens later than before. This is necessary so that we have everything in place to construct the `CreateTimelineIdempotency`. Notably, this moves the acquisition of the creation guard _after_ the acquisition of the `gc_cs` lock in the case of branching. This might appear as if we're at risk of holding `gc_cs` longer than before this PR, but, even before this PR, we were holding `gc_cs` until after the `wait_completion()` that makes the timeline creation durable in S3 returns. I don't see any deadlock risk with reversing the lock acquisition order. As a drive-by change, I found that the `create_timeline()` function in `neon_local` is unused, so I removed it. # Refs * platform context: https://github.com/neondatabase/neon/pull/9218 * product context: https://github.com/neondatabase/cloud/issues/17507 * next PR stacked atop this one: https://github.com/neondatabase/neon/pull/9501