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Merged
hubcio merged 2 commits into from
Mar 17, 2026
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docs(connectors): align MongoDB sink duplicate-key semantics #2941

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docs(connectors): align MongoDB sink duplicate-key semantics
avirajkhare00 Mar 16, 2026
686d7bc
Merge branch 'master' into mongodb-sink-contract-alignment
avirajkhare00 Mar 17, 2026
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9 changes: 5 additions & 4 deletions core/connectors/sinks/mongodb_sink/README.md
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Expand Up @@ -137,10 +137,11 @@ This connector provides **at-least-once** delivery semantics.
### Behavior

- Messages may be delivered more than once on retry or restart
- Uses Iggy message ID as MongoDB `_id` for document identity
- **Insert-only mode**: duplicate key error is a hard failure (not upsert)
- Uses a deterministic composite MongoDB `_id`: `stream:topic:partition:message_id`
- Duplicate key collisions are treated as idempotent replay of already-written messages
- The sink remains insert-only; it does not upsert existing documents

### Known Limitations

- On network timeout during insert, retry may cause duplicate key error
- Sink does not upsert on duplicate (future improvement)
- On network timeout during insert, MongoDB may partially commit a batch before returning an error
- The sink does not upsert on duplicate; replay safety relies on deterministic `_id` values and duplicate-key tolerance
2 changes: 1 addition & 1 deletion core/integration/tests/connectors/mongodb/mongodb_sink.rs
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Expand Up @@ -261,7 +261,7 @@ async fn large_batch_processed_correctly(harness: &TestHarness, fixture: MongoDb
server(connectors_runtime(config_path = "tests/connectors/mongodb/sink.toml")),
seed = seeds::connector_stream
)]
async fn duplicate_key_is_explicit_failure_and_not_silent_success(
async fn duplicate_key_is_idempotent_replay_not_sink_error(
harness: &TestHarness,
fixture: MongoDbSinkFixture,
) {
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