# Pinned event-mongodb transaction context and checkpoint write boundaries > Source-anchored research for Pinned event-mongodb transaction context and checkpoint write boundaries. Run status: COMPLETED. Parent: [Change Data Capture Patterns](https://llms-explorer.com/tree/change-data-capture-patterns/) · 4 facets · 12 facts · page: https://llms-explorer.com/tree/pinned-event-mongodb-transaction-context-and-checkpoint-write-boundaries/ ## Structure and components - Across the complete inspected transaction fixture file, the cases insert test documents into a docs collection and check their presence after commit or rollback. This file contains no combined marker/projection/checkpoint crash-replay scenario and no case calling ExecuteWithContext. The inspected marker and checkpoint write bodies pass their supplied context to separate driver writes. These source observations do not demonstrate three-record co-commit, uncertain-commit recovery, old-duplicate handling, revision fencing or a complete replay protocol. (medium confidence) — [source](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/transaction/mongodb_integration_test.go) · [also](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/transaction/mongodb.go) · [also](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/idempotency/mongodb.go) · [also](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/checkpoint/mongodb.go) ## Problems, failure modes and limitations - `Execute` uses `session.WithTransaction`; its callback wraps the driver callback context in `MongoTransaction` and passes the transaction object to `fn`. `ExecuteWithContext` instead passes the driver callback context directly to `fn`. Both defer session cleanup and return the driver transaction error. (low confidence) — [source](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/transaction/mongodb.go) - The checkpoint methods pass the supplied context to driver operations: EnsureIndexes uses CreateMany; Load and GetCheckpointInfo use FindOne; Delete uses DeleteOne; DeleteAll uses DeleteMany; and List and GetAll use Find and use the context again during cursor traversal and closure. Load returns zero time with no error for ErrNoDocuments. These complete method bodies create no session-bearing context. (low confidence) — [source](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/checkpoint/mongodb.go) - The Execute fixtures type-assert the transaction argument to MongoSessionProvider and insert using mtx.Context(). The success case asserts that the document is present; the case whose callback returns a sentinel error asserts that the document is absent. (low confidence) — [source](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/transaction/mongodb_integration_test.go) - The WithTransaction helper fixtures use the callback context for coll.InsertOne. The success case expects one matching document and the callback-error case expects none. The setup comment says tests are skipped when MongoDB is unavailable or short mode is set, and the cases explicitly skip unsupported-transaction deployment errors. (low confidence) — [source](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/transaction/mongodb_integration_test.go) ## Comparisons and alternatives - IsDuplicate and IsDuplicateTx forward the supplied context to the same helper. That helper passes the context, expiry filter, update and upsert options to coll.FindOneAndUpdate. It treats duplicate-key or no-document errors as duplicate results and returns false after a successful write. This duplicate check writes state rather than performing only a read. (low confidence) — [source](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/idempotency/mongodb.go) ## Facts and statements - In the pinned implementation, `Begin` starts a session and transaction, then stores `mongo.NewSessionContext(ctx, session)` in the returned `MongoTransaction`. The source warns that writes using a context without the session auto-commit outside that transaction. (low confidence) — [source](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/transaction/mongodb.go) - The Context method of MongoTransaction returns its stored t.ctx. MongoSessionProvider embeds the generic transaction interface and exposes Session and Context methods for MongoDB-specific access; the manual fixtures access that interface by type assertion. (medium confidence) — [source](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/transaction/mongodb.go) · [also](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/transaction/mongodb_integration_test.go) - The Commit method calls t.session.CommitTransaction with t.ctx, and the Rollback method calls t.session.AbortTransaction with t.ctx. Both then call t.endSession. The wrapper has a sync.Once field named closeOnce; endSession calls t.session.EndSession through t.closeOnce.Do. (low confidence) — [source](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/transaction/mongodb.go) - MarkProcessed delegates to MarkProcessedWithTTL. MarkProcessedTx and MarkProcessedWithTTLTx share markProcessedWithCollection, which computes processed and expiry timestamps and calls ReplaceOne(ctx, {"_id": messageID}, entry, options.Replace().SetUpsert(true)). These marker methods pass the supplied context; they do not start a session or transaction themselves. (low confidence) — [source](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/idempotency/mongodb.go) - Checkpoint Save stores the subscriber ID, supplied time position and current update time through s.collection.ReplaceOne using the supplied context and upsert enabled. The filter is bson.M{"_id": subscriberID}. Within this complete method body, there is no revision comparison, monotonic-position guard or transaction start. (low confidence) — [source](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/checkpoint/mongodb.go) - The manual transaction fixtures obtain MongoSessionProvider by type assertion and insert using mtx.Context(). They call tx.Rollback() or tx.Commit() and assert respectively an absent or present document. These statements describe expectations in fixture source. (low confidence) — [source](https://raw.githubusercontent.com/rbaliyan/event-mongodb/ca444aedec31e7e959c0932a8f7577c15312f37e/transaction/mongodb_integration_test.go)