test(pageserver): check retain_lsn after offload #9753
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Signed-off-by: Alex Chi Z <chi@neon.tech>
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528749b at 2024-11-13T22:22:24.426Z :recycle: |
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Nov 15, 2024
PR #9308 has modified tenant activation code to take offloaded child timelines into account for populating the list of `retain_lsn` values. However, there is more places than just tenant activation where one needs to update the `retain_lsn`s. This PR fixes some bugs of the current code that could lead to corruption in the worst case: 1. Deleting of an offloaded timeline would not get its `retain_lsn` purged from its parent. With the patch we now do it, but as the parent can be offloaded as well, the situatoin is a bit trickier than for non-offloaded timelines which can just keep a pointer to their parent. Here we can't keep a pointer because the parent might get offloaded, then unoffloaded again, creating a dangling pointer situation. Keeping a pointer to the *tenant* is not good either, because we might drop the offloaded timeline in a context where a `offloaded_timelines` lock is already held: so we don't want to acquire a lock in the drop code of OffloadedTimeline. 2. Unoffloading a timeline would not get its `retain_lsn` values populated, leading to it maybe garbage collecting values that its children might need. We now call `initialize_gc_info` on the parent. 3. Offloading of a timeline would not get its `retain_lsn` values registered as offloaded at the parent. So if we drop the `Timeline` object, and its registration is removed, the parent would not have any of the child's `retain_lsn`s around. Also, before, the `Timeline` object would delete anything related to its timeline ID, now it only deletes `retain_lsn`s that have `MaybeOffloaded::No` set. Incorporates Chi's reproducer from #9753. cc neondatabase/cloud#20199 The `test_timeline_retain_lsn` test is extended: 1. it gains a new dimension, duplicating each mode, to either have the "main" branch be the direct parent of the timeline we archive, or the "test_archived_parent" branch intermediary, creating a three timeline structure. This doesn't test anything fixed by this PR in particular, just explores the vast space of possible configurations a little bit more. 2. it gains two new modes, `offload-parent`, which tests the second point, and `offload-no-restart` which tests the third point. It's easy to verify the test actually is "sharp" by removing one of the respective `self.initialize_gc_info()`, `gc_info.insert_child()` or `ancestor_children.push()`. Part of #8088 --------- Signed-off-by: Alex Chi Z <chi@neon.tech> Co-authored-by: Alex Chi Z <chi@neon.tech>
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