# Replica Set Transactions > Source-anchored research for Replica Set Transactions. Run status: COMPLETED. Parent: [MongoDB Transactions](https://llms-explorer.com/tree/mongodb-transactions/) · 3 facets · 14 facts · page: https://llms-explorer.com/tree/replica-set-transactions/ ## How it works - MongoDB Jira issue SERVER-88746 documents a snapshot-isolation violation in replica-set transactions on version 7.0.0 when writes raced with a collection drop or rename; the issue lists 7.0.10 as the fix version. (low confidence) (verified as of 2024-05-06) — [source](https://jira.mongodb.org/browse/SERVER-88746) - With transaction commit write concern w:1, MongoDB acknowledges after the primary applies the commit, so a failover can roll the transaction back before replication; when the former primary rejoins, it reverts writes that were not replicated to secondaries. (high confidence) — [source](https://www.mongodb.com/docs/manual/core/transactions.md) - Transaction-level read concern snapshot or majority guarantees majority-committed reads only when commit uses write concern majority; without majority at commit, those read concerns alone do not provide that guarantee. (high confidence) — [source](https://www.mongodb.com/docs/manual/core/transactions.md) ## Comparisons and alternatives - MongoDB keeps a replica-set transaction's changes invisible to outside operations until commit; on commit, all changes become visible together rather than as a partial subset. (high confidence) — [source](https://www.mongodb.com/docs/manual/core/transactions.md) ## Facts and statements - MongoDB’s production manual says standalone deployments do not support transactions and that replica sets support multi-document transactions. (low confidence) — [source](https://www.mongodb.com/docs/manual/core/transactions-production-consideration/) - The current production manual requires every replica-set member to have featureCompatibilityVersion 4.0 or later for transactions. (low confidence) (verified as of 2026-10-20) — [source](https://www.mongodb.com/docs/manual/core/transactions-production-consideration/) - A transaction containing reads must use read preference primary, and all operations in that transaction route to the same replica-set member. (high confidence) — [source](https://www.mongodb.com/docs/manual/core/transactions.md) - Within a transaction, readConcern snapshot guarantees a snapshot of majority-committed data only if commitTransaction uses writeConcern majority; without majority at commit, that guarantee does not hold. (high confidence) — [source](https://www.mongodb.com/docs/manual/core/transactions.md) - A transaction committed with writeConcern w:1 can be rolled back after failover; writeConcern majority acknowledges after the commit is applied to a majority of voting members. (high confidence) — [source](https://www.mongodb.com/docs/manual/core/transactions.md) - A 2022 formal-verification paper models the REPLICASET transaction protocol separately and reports that it satisfies a Strong-SI variant of snapshot isolation under the paper’s formal model. (low confidence) — [source](https://arxiv.org/abs/2111.14946) - Jepsen’s MongoDB 4.2.6 evaluation found snapshot-isolation anomalies, but it tested a two-shard cluster whose config replica set and data shards each had three members, so it does not isolate replica-set-only transactions. (high confidence) — [source](https://jepsen.io/analyses/mongodb-4.2.6) - MongoDB's replication README says durability of a single replica-set transaction is not guaranteed until commitTransaction is majority committed; it also says unprepared transactions in progress are aborted during stepdown and are not recovered on failover. (high confidence) — [source](https://github.com/mongodb/mongo/blob/master/src/mongo/db/repl/README.md) - A 2022 formal-verification paper models MongoDB's replica-set transaction protocol from documentation and source code and reports that its REPLICASET model satisfies Realtime-SI. (medium confidence) — [source](https://arxiv.org/abs/2111.14946) - MongoDB documents an exception to majority durability: if writeConcernMajorityJournalDefault is false, a transient loss of a majority of replica-set nodes can still allow majority-acknowledged writes to roll back. (high confidence) (verified as of 2026-10-14) — [source](https://www.mongodb.com/docs/manual/core/replica-set-rollbacks.md)