MongoDB to GCS
real-time replication
TwinCommit replicates MongoDB to Google Cloud Storage in real time by reading the MongoDB transaction log and applying every committed change exactly once and in commit order. Use it to land live MongoDB data in GCS as open Delta Lake or Iceberg tables, with no triggers or capture tables on the source.
MongoDB
log reader
commit-ordered · exactly-once
GCS
native writer
How capture works on MongoDB
TwinCommit opens change streams on replica sets and sharded clusters, persists resume tokens with the checkpoint, and keeps multi-document transactions intact.
Prerequisites
- ✓Replica set or sharded cluster (change streams need an oplog)
- ✓changeStream and find privileges on watched databases
- ✓Pre- and post-images enabled for full before/after values (optional)
How apply works on GCS
Changes land as Apache Iceberg, Delta Lake or Parquet tables with one atomic commit per micro-batch. Iceberg tables register in the BigLake metastore so BigQuery can query them in place.
Requirements
- ✓Storage Object Admin on the bucket
- ✓BigLake Admin for catalog registration (optional)
- ✓Workload identity or a service-account key
Setup
Set up MongoDB → GCS in four steps
- 1
Prepare MongoDB
Run twincommit check. It verifies replica set or sharded cluster (change streams need an oplog) and the other prerequisites, and prints the exact fix for anything missing.
- 2
Point at GCS
Add a target block for GCS. TwinCommit can generate target DDL with twincommit ddl -apply.
- 3
Snapshot
twincommit snapshot copies each table under a brief share lock and records the exact log position.
- 4
Stream
twincommit run streams every committed change from that position, exactly once and in commit order.
source:
type: mongodb
uri: ${MONGODB_URI}
target:
type: gcs
bucket: acme-lake
path: replica/{schema}/{table}
format: iceberg
catalog: { type: biglake, project: acme-analytics }
tables:
- source: sales.orders
- source: sales.customersMongoDB to GCS replication FAQ
How does TwinCommit replicate MongoDB to GCS?
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TwinCommit reads changes from the MongoDB transaction log, buffers them per transaction, and applies each committed transaction to GCS in commit order. Changes land as Apache Iceberg, Delta Lake or Parquet tables with one atomic commit per micro-batch. Iceberg tables register in the BigLake metastore so BigQuery can query them in place.
Does MongoDB to GCS replication need triggers or capture tables?
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No. TwinCommit reads the MongoDB log directly and creates no objects in the source database.
Is MongoDB to GCS replication exactly-once?
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Yes. TwinCommit commits its checkpoint in the same GCS transaction as the data, so a crash or restart never loses or duplicates a transaction.
What MongoDB versions are supported?
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MongoDB 5.0–8.x · MongoDB Atlas · replica sets and sharded clusters.
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