- select_next_unit catalogues the legacy partition as soon as it is attached and takes a unit when its own upper bound is past the window, so the catch-up of pre-swap history starts when retention is enabled instead of one window after the swap time. The partition drop still waits for every sub-range, so the last one, ending at the swap time, holds the detach for a window.
- retention_health computes oldest_eligible_age by sub-range for a legacy partition with catalog rows (_eligible_uppers), and by partition bound otherwise.
- Tests: the early catalogue and the per-sub-range selection.
- Docs: the how-to, reference, explanation and ADR 42 state the per-unit rule.
tazlin
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