fix: validate snapshot is unreferenced before expiration removal#716
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dhananjaykrutika wants to merge 2 commits intoapache:mainfrom
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fix: validate snapshot is unreferenced before expiration removal#716dhananjaykrutika wants to merge 2 commits intoapache:mainfrom
dhananjaykrutika wants to merge 2 commits intoapache:mainfrom
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added 2 commits
February 6, 2026 12:16
Snapshot expiration maintenance can race with concurrent client commits that reference the same snapshot being expired. Consider: 1. Maintenance identifies snap-1 as expired and eligible for removal 2. Client commits AddSnapshotRef linking snap-1 to "feature-branch" 3. Maintenance loads metadata (now contains feature-branch → snap-1) 4. Maintenance commits RemoveSnapshot for snap-1 The CAS succeeds because maintenance has the latest pointer, but the resulting metadata is corrupt: feature-branch references a deleted snapshot. CAS only guarantees the pointer hasn't changed since we read it - it does not validate that our operation is semantically correct against the current state. By checking isSnapshotReferenced() against the freshly loaded metadata, we detect that snap-1 is now in use and skip its removal. The CAS then guarantees this validated state remains current through the commit.
zeroshade
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Feb 6, 2026
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Looks good overall, just one nitpick
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| for _, ref := range b.refs { | ||
| if ref.SnapshotID == snapshotID { | ||
| return true | ||
| } | ||
| } | ||
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| return false |
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could this be replaced with just slices.ContainsFunc(b.refs, func(r Ref) bool { return r.SnapshotID == snapshotID })?
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Abandoning it in favor of #720 |
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Snapshot expiration maintenance can race with concurrent client commits that reference the same snapshot being expired. Consider:
The CAS succeeds because maintenance has the latest pointer, but the resulting metadata is corrupt: feature-branch references a deleted snapshot.
CAS only guarantees the pointer hasn't changed since we read it - it does not validate that our operation is semantically correct against the current state. By checking isSnapshotReferenced() against the freshly loaded metadata, we detect that snap-1 is now in use and skip its removal. The CAS then guarantees this validated state remains current through the commit.