MongoDB to Cassandra
real-time replication
TwinCommit replicates MongoDB to Apache Cassandra in real time by reading the MongoDB transaction log and applying every committed change exactly once and in commit order. Use it to serve MongoDB data from Cassandra at scale without dual writes, with no triggers or capture tables on the source.
MongoDB
log reader
commit-ordered · exactly-once
Cassandra
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 Cassandra
Batched upserts and deletes use the source commit timestamp as the Cassandra write timestamp, so replays are idempotent and newer data always wins.
Requirements
- ✓cdc_enabled: true in cassandra.yaml
- ✓WITH cdc = true on replicated tables
- ✓Agent sidecar or shared volume access to cdc_raw on each node
Setup
Set up MongoDB → Cassandra 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 Cassandra
Add a target block for Cassandra. 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: cassandra
contact_points: [cass-1, cass-2, cass-3]
keyspace: replica
consistency: LOCAL_QUORUM
tables:
- source: sales.orders
- source: sales.customersMongoDB to Cassandra replication FAQ
How does TwinCommit replicate MongoDB to Cassandra?
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TwinCommit reads changes from the MongoDB transaction log, buffers them per transaction, and applies each committed transaction to Cassandra in commit order. Batched upserts and deletes use the source commit timestamp as the Cassandra write timestamp, so replays are idempotent and newer data always wins.
Does MongoDB to Cassandra 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 Cassandra replication exactly-once?
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Yes. TwinCommit commits its checkpoint in the same Cassandra 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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