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pageserver: remove paranoia double-calculation of retain_lsns (#8617)

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## Problem

This code was to mitigate risk in
https://github.com/neondatabase/neon/pull/8427

As expected, we did not hit this code path - the new continuous updates
of gc_info are working fine, we can remove this code now.

## Summary of changes

- Remove block that double-checks retain_lsns
This commit is contained in:
John Spray
2024-08-08 12:57:48 +01:00
parent 552832b819
commit 56077caaf9
1 changed files with 0 additions and 48 deletions
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48
pageserver/src/tenant.rs
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@@ -3012,54 +3012,6 @@ impl Tenant {
// because that will stall branch creation.
let gc_cs = self.gc_cs.lock().await;
// Paranoia check: it is critical that GcInfo's list of child timelines is correct, to avoid incorrectly GC'ing data they
// depend on. So although GcInfo is updated continuously by Timeline::new and Timeline::drop, we also calculate it here
// and fail out if it's inaccurate.
// (this can be removed later, it's a risk mitigation for https://github.com/neondatabase/neon/pull/8427)
{
let mut all_branchpoints: BTreeMap<TimelineId, Vec<(Lsn, TimelineId)>> =
BTreeMap::new();
timelines.iter().for_each(|timeline| {
if let Some(ancestor_timeline_id) = &timeline.get_ancestor_timeline_id() {
let ancestor_children =
all_branchpoints.entry(*ancestor_timeline_id).or_default();
ancestor_children.push((timeline.get_ancestor_lsn(), timeline.timeline_id));
}
});
for timeline in &timelines {
let mut branchpoints: Vec<(Lsn, TimelineId)> = all_branchpoints
.remove(&timeline.timeline_id)
.unwrap_or_default();
branchpoints.sort_by_key(|b| b.0);
let target = timeline.gc_info.read().unwrap();
// We require that retain_lsns contains everything in `branchpoints`, but not that
// they are exactly equal: timeline deletions can race with us, so retain_lsns
// may contain some extra stuff. It is safe to have extra timelines in there, because it
// just means that we retain slightly more data than we otherwise might.
let have_branchpoints = target.retain_lsns.iter().copied().collect::<HashSet<_>>();
for b in &branchpoints {
if !have_branchpoints.contains(b) {
tracing::error!(
"Bug: `retain_lsns` is set incorrectly. Expected be {:?}, but found {:?}",
branchpoints,
target.retain_lsns
);
debug_assert!(false);
// Do not GC based on bad information!
// (ab-use an existing GcError type rather than adding a new one, since this is a
// "should never happen" check that will be removed soon).
return Err(GcError::Remote(anyhow::anyhow!(
"retain_lsns failed validation!"
)));
}
}
}
}
// Ok, we now know all the branch points.
// Update the GC information for each timeline.
let mut gc_timelines = Vec::with_capacity(timelines.len());