Correct mistakes in offloaded timeline retain_lsn management #9760
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Signed-off-by: Alex Chi Z <[email protected]>
This doesn't actually reproduce any of the issues I've just fixed. Probably the timeline is still referenced somewhere and thus not dropped?
skyzh
approved these changes
Nov 14, 2024
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LGTM; overall I feel we might want to revisit the retain_lsn mechanism, manipulating it in Drop doesn't seem like a good idea... As we get more and more timeline states, in the future, probably it would be a good idea to re-compute it every time before gc/compaction?
I actually thought that this was already done, due to #9308. Personally I'd be fine with that as well. |
But this is done in |
yeah, that's what I wanted to say: i mistakenly assumed this when I wrote #9308. Now I know better :) |
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5490 tests run: 5247 passed, 0 failed, 243 skipped (full report)Code coverage* (full report)
* collected from Rust tests only The comment gets automatically updated with the latest test results
cef74a5 at 2024-11-15T12:59:31.645Z :recycle: |
Not sure why we can read the basebackup, but shrug.
|
Documenting the test failures if I comment out the offloading-specific commented out commented out commented out diff --git a/pageserver/src/tenant.rs b/pageserver/src/tenant.rs
index 909f99ea9..27de8c2ba 100644
--- a/pageserver/src/tenant.rs
+++ b/pageserver/src/tenant.rs
@@ -542,7 +542,7 @@ fn from_timeline(timeline: &Timeline) -> Result<Self, UploadQueueNotReadyError>
let ancestor_lsn = timeline.get_ancestor_lsn();
let ancestor_timeline_id = ancestor_timeline.timeline_id;
let mut gc_info = ancestor_timeline.gc_info.write().unwrap();
- gc_info.insert_child(timeline.timeline_id, ancestor_lsn, MaybeOffloaded::Yes);
+ //gc_info.insert_child(timeline.timeline_id, ancestor_lsn, MaybeOffloaded::Yes);
(Some(ancestor_lsn), Some(ancestor_timeline_id))
} else {
(None, None)
@@ -1988,7 +1988,7 @@ async fn unoffload_timeline(
None => warn!("timeline already removed from offloaded timelines"),
}
- self.initialize_gc_info(&timelines, &offloaded_timelines, Some(timeline_id));
+ //self.initialize_gc_info(&timelines, &offloaded_timelines, Some(timeline_id));
Arc::clone(timeline)
};
@@ -3865,7 +3865,7 @@ fn initialize_gc_info(
return;
};
let ancestor_children = all_branchpoints.entry(*ancestor_timeline_id).or_default();
- ancestor_children.push((retain_lsn, *timeline_id, MaybeOffloaded::Yes));
+ //ancestor_children.push((retain_lsn, *timeline_id, MaybeOffloaded::Yes));
});
// The number of bytes we always keep, irrespective of PITR: this is a constant across timelines |
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PR #9308 has modified tenant activation code to take offloaded child timelines into account for populating the list of
retain_lsnvalues. However, there is more places than just tenant activation where one needs to update theretain_lsns.This PR fixes some bugs of the current code that could lead to corruption in the worst case:
retain_lsnpurged 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 aoffloaded_timelineslock is already held: so we don't want to acquire a lock in the drop code of OffloadedTimeline.retain_lsnvalues populated, leading to it maybe garbage collecting values that its children might need. We now callinitialize_gc_infoon the parent.retain_lsnvalues registered as offloaded at the parent. So if we drop theTimelineobject, and its registration is removed, the parent would not have any of the child'sretain_lsns around. Also, before, theTimelineobject would delete anything related to its timeline ID, now it only deletesretain_lsns that haveMaybeOffloaded::Noset.Incorporates Chi's reproducer from #9753. cc https://github.com/neondatabase/cloud/issues/20199
The
test_timeline_retain_lsntest is extended:offload-parent, which tests the second point, andoffload-no-restartwhich 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()orancestor_children.push().Part of #8088