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tka: mark young AUMs as active even if the chain is long

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Existing compaction logic seems to have had an assumption that
markActiveChain would cover a longer part of the chain than
markYoungAUMs. This prevented long, but fresh, chains, from being
compacted correctly.

Updates tailscale/corp#33537

Signed-off-by: Anton Tolchanov <anton@tailscale.com>
This commit is contained in:
Anton Tolchanov
2025-11-18 17:04:08 +00:00
committed by Anton Tolchanov
parent bd29b189fe
commit 04a9d25a54
2 changed files with 45 additions and 11 deletions
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tka/tailchonk.go
+14 -11
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@@ -668,7 +668,7 @@ const (
)
// markActiveChain marks AUMs in the active chain.
// All AUMs that are within minChain ancestors of head are
// All AUMs that are within minChain ancestors of head, or are marked as young, are
// marked retainStateActive, and all remaining ancestors are
// marked retainStateCandidate.
//
@@ -700,19 +700,22 @@ func markActiveChain(storage Chonk, verdict map[AUMHash]retainState, minChain in
// If we got this far, we have at least minChain AUMs stored, and minChain number
// of ancestors have been marked for retention. We now continue to iterate backwards
// till we find an AUM which we can compact to (a Checkpoint AUM).
// till we find an AUM which we can compact to: either a Checkpoint AUM which is old
// enough, or the genesis AUM.
for {
h := next.Hash()
verdict[h] |= retainStateActive
if next.MessageKind == AUMCheckpoint {
lastActiveAncestor = h
break
}
parent, hasParent := next.Parent()
if !hasParent {
return AUMHash{}, errors.New("reached genesis AUM without finding an appropriate lastActiveAncestor")
isYoung := verdict[h]&retainStateYoung != 0
if next.MessageKind == AUMCheckpoint {
lastActiveAncestor = h
if !isYoung || !hasParent {
break
}
}
if next, err = storage.AUM(parent); err != nil {
return AUMHash{}, fmt.Errorf("searching for compaction target (%v): %w", parent, err)
}
@@ -917,12 +920,12 @@ func Compact(storage CompactableChonk, head AUMHash, opts CompactionOptions) (la
verdict[h] = 0
}
if lastActiveAncestor, err = markActiveChain(storage, verdict, opts.MinChain, head); err != nil {
return AUMHash{}, fmt.Errorf("marking active chain: %w", err)
}
if err := markYoungAUMs(storage, verdict, opts.MinAge); err != nil {
return AUMHash{}, fmt.Errorf("marking young AUMs: %w", err)
}
if lastActiveAncestor, err = markActiveChain(storage, verdict, opts.MinChain, head); err != nil {
return AUMHash{}, fmt.Errorf("marking active chain: %w", err)
}
if err := markDescendantAUMs(storage, verdict); err != nil {
return AUMHash{}, fmt.Errorf("marking descendant AUMs: %w", err)
}