PostgreSQL to Cassandra
real-time replication
TwinCommit replicates PostgreSQL to Apache Cassandra in real time by reading the PostgreSQL transaction log and applying every committed change exactly once and in commit order. Use it to serve PostgreSQL data from Cassandra at scale without dual writes, with no triggers or capture tables on the source.
PostgreSQL
log reader
commit-ordered · exactly-once
Cassandra
native writer
How capture works on PostgreSQL
TwinCommit uses a logical replication slot with the built-in pgoutput plugin, so there is nothing to install on the server.
Prerequisites
- ✓wal_level = logical
- ✓REPLICATION privilege
- ✓Primary key or REPLICA IDENTITY FULL
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 PostgreSQL → Cassandra in four steps
- 1
Prepare PostgreSQL
Run twincommit check. It verifies wal_level = logical 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: postgres
dsn: ${SOURCE_DSN}
slot: twincommit
target:
type: cassandra
contact_points: [cass-1, cass-2, cass-3]
keyspace: replica
consistency: LOCAL_QUORUM
tables:
- source: SALES.ORDERS
- source: SALES.ORDER_LINES
exclude_columns: [INTERNAL_NOTES]PostgreSQL to Cassandra replication FAQ
How does TwinCommit replicate PostgreSQL to Cassandra?
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TwinCommit reads changes from the PostgreSQL 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 PostgreSQL to Cassandra replication need triggers or capture tables?
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No. TwinCommit reads the PostgreSQL log directly and creates no objects in the source database.
Is PostgreSQL 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 PostgreSQL versions are supported?
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PostgreSQL 13–18 · Amazon RDS and Aurora · Azure Flexible Server · Cloud SQL · AlloyDB.
Stream PostgreSQL to Cassandra today.
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