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## Problem We already made a change in #6407 to make pitr_interval authoritative for synthetic size calculations (do not charge users for data retained due to gc_horizon), but that change didn't cover the case where someone entirely disables time-based retention by setting pitr_interval=0 Relates to: https://github.com/neondatabase/neon/issues/6374 ## Summary of changes When pitr_interval is zero, do not set `pitr_cutoff` based on gc_horizon. gc_horizon is still enforced, but separately (its value is passed separately, there was never a need to claim pitr_cutoff to gc_horizon) ## More detail ### Issue 1 Before this PR, we would skip the update_gc_info for timelines with last_record_lsn() < gc_horizon. Let's call such timelines "tiny". The rationale for that presumably was that we can't GC anything in the tiny timelines, why bother to call update_gc_info(). However, synthetic size calculation relies on up-to-date update_gc_info() data. Before this PR, tiny timelines would never get an updated GcInfo::pitr_horizon (it remained Lsn(0)). Even on projects with pitr_interval=0d. With this PR, update_gc_info is always called, hence GcInfo::pitr_horizon is always updated, thereby providing synthetic size calculation with up-to-data data. ### Issue 2 Before this PR, regardless of whether the timeline is "tiny" or not, GcInfo::pitr_horizon was clamped to at least last_record_lsn - gc_horizon, even if the pitr window in terms of LSN range was shorter (=less than) the gc_horizon. With this PR, that clamping is removed, so, for pitr_interval=0, the pitr_horizon = last_record_lsn.