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Type: Task
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Resolution: Done
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Priority: Major - P3
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Affects Version/s: None
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Labels:None
Description
Transaction snapshot reads are now banned on capped collections.
Description of Linked Ticket
Capped collections typically (always?) delete records with an unreplicated/untimestamped write. Those deletions will always become visible in a newer transaction. So if a transaction uses snapshot with an atClusterTime (e.g. coming from mongos), it may not see some deleted documents even if they existed at the point in time requested.
Snapshot transactions without atClusterTime might still work if the snapshot is open before the deletions happen probably because they hold onto the WT txn and the snapshot. But I am not 100% sure. Either way, it seems that we will still have to ban transaction snapshot reads on capped collections unless we choose to timestamp the capped collection deletions.
Scope of changes
Pages to review and update:
- https://docs.mongodb.com/manual/reference/read-concern-snapshot/
- https://docs.mongodb.com/manual/core/capped-collections/
- https://docs.mongodb.com/manual/core/transactions-operations/
Impact to Other Docs
MVP (Work and Date)
Resources (Scope or Design Docs, Invision, etc.)
- documents
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SERVER-47824 Ban transaction snapshot reads on capped collections
- Closed