MongoDB

MongoDB is a document-oriented database that stores data as flexible JSON-like documents. It is widely used for applications that need schema flexibility, horizontal scaling, and the ability to store nested, hierarchical data naturally. When pg_tide delivers messages to MongoDB, your PostgreSQL events are written as documents to a collection, where they can be queried with MongoDB's rich query language, aggregated for analytics, or used to maintain a read-optimized view of your data.

When to Use This Sink

Choose MongoDB when your downstream consumers use MongoDB as their primary data store, when you want to maintain a denormalized read model of your PostgreSQL data in a document database, or when you need flexible schema storage for event data that evolves rapidly. MongoDB's document model maps naturally to JSON event payloads without requiring a predefined schema.

Configuration

SELECT tide.relay_set_outbox(
    'events-to-mongo',
    'events',
    'mongo-relay',
    '{
        "sink_type": "mongodb",
        "connection_string": "${env:MONGODB_URI}",
        "database": "events",
        "collection": "outbox_events",
        "batch_size": 500,
        "write_concern": "majority"
    }'::jsonb
);

Configuration Reference

Parameter	Type	Default	Description
`sink_type`	string	—	Must be `"mongodb"`
`connection_string`	string	—	MongoDB connection URI
`database`	string	—	Target database
`collection`	string	—	Target collection
`batch_size`	int	`500`	Documents per bulk write
`write_concern`	string	`"majority"`	Write concern level
`upsert`	bool	`false`	Use upsert mode (update if exists, insert if not)
`upsert_key`	string	`"dedup_key"`	Field used as document ID for upserts

Upsert Mode

When upsert: true, the relay uses the dedup_key as the document _id. This provides natural deduplication — re-delivered messages update the existing document rather than creating duplicates. This is particularly useful for maintaining a current-state view of entities:

{
    "sink_type": "mongodb",
    "connection_string": "mongodb+srv://...",
    "database": "orders",
    "collection": "current_state",
    "upsert": true,
    "upsert_key": "dedup_key"
}

Delivery Guarantees

With write_concern: "majority", MongoDB acknowledges writes only after they are replicated to a majority of replica set members, providing durable at-least-once delivery. With upsert mode, re-delivery is idempotent.

Troubleshooting

"Authentication failed" — Check credentials in the connection string and verify the user has write access
"Connection timeout" — Verify network connectivity; for Atlas, ensure your IP is in the access list
"Write concern timeout" — Replica set members are unavailable; check cluster health

pg_tide Documentation