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The MOLT (Migrate Off Legacy Technology) toolkit enables safe, minimal-downtime database migrations to CockroachDB. MOLT combines schema transformation, distributed data load, continuous replication, and row-level validation into a highly configurable workflow that adapts to diverse production environments.

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Migration sequence

Before you begin the migration, review the Migration Strategy guide.
A migration to CockroachDB generally follows this sequence:
1

Prepare the source database

Configure users, permissions, and replication settings as needed.
2

Convert the source schema

Use the Schema Conversion Tool to generate CockroachDB-compatible DDL. Apply the converted schema to the target database. Drop constraints and indexes to facilitate data load.
3

Load data into CockroachDB

Use MOLT Fetch to bulk-ingest your source data.
4

Verify consistency (optional)

Use MOLT Verify to confirm that the data loaded into CockroachDB is consistent with the source.
5

Finalize target schema

Recreate indexes or constraints on CockroachDB that you previously dropped to facilitate data load.
6

Replicate ongoing changes

Enable continuous replication with MOLT Replicator to keep CockroachDB in sync with the source.
7

Verify consistency before cutover

Use MOLT Verify to confirm that the CockroachDB data is consistent with the source.
8

Cut over to CockroachDB

Redirect application traffic to the CockroachDB cluster.

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MOLT tools

MOLT is a set of tools for schema conversion, data load, replication, and validation. Migrations with MOLT are resilient, restartable, and scalable to large data sets.

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Schema Conversion Tool

The MOLT Schema Conversion Tool converts a source database schema to a CockroachDB-compatible schema. The tool performs the following actions:
  • Identifies unimplemented features
  • Rewrites unsupported DDL syntax
  • Applies CockroachDB schema best practices
Supported sources: PostgreSQL, MySQL, Oracle, SQL Server Release status: GA (Cloud only)

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MOLT Fetch

MOLT Fetch performs the initial data load to CockroachDB. It supports:
  • Multiple migration flows via IMPORT INTO or COPY FROM
  • Data movement via cloud storage, local file servers, or direct copy
  • Concurrent data export from multiple source tables and shards
  • Schema transformation rules
  • Safe continuation to retry failed or interrupted tasks from specific checkpoints
Supported sources: PostgreSQL 11-16, MySQL 5.7-8.0+, Oracle Database 19c (Enterprise Edition) and 21c (Express Edition), CockroachDB Release status: GA

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MOLT Replicator

MOLT Replicator provides continuous replication capabilities for minimal-downtime migrations. It supports:
  • Continuous replication from source databases to CockroachDB
  • Multiple consistency modes for balancing throughput and transactional guarantees
  • Failback replication from CockroachDB back to source databases
  • Performance tuning for high-throughput workloads
Supported sources: CockroachDB, PostgreSQL 11-16, MySQL 5.7+ and 8.0+, Oracle Database 19c+ Release status: GA

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MOLT Verify

MOLT Verify checks for data and schema discrepancies between the source database and CockroachDB. It performs the following verifications:
  • Table structure
  • Column definition
  • Row-level data
Supported sources: PostgreSQL 12-16, MySQL 5.7-8.0+, Oracle Database 19c (Enterprise Edition) and 21c (Express Edition), CockroachDB Release status: Preview

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Migration flows

MOLT supports various migration flows using MOLT Fetch for data loading and MOLT Replicator for ongoing replication.
Migration flowToolsDescriptionBest for
Bulk loadMOLT FetchPerform a one-time bulk load of source data into CockroachDB.Testing, migrations with planned downtime
Data load and replicationMOLT Fetch + MOLT ReplicatorLoad source data with Fetch, then replicate subsequent changes continuously with Replicator.Minimal downtime migrations
Resume replicationMOLT ReplicatorResume replication from a checkpoint after interruption.Resuming interrupted migrations, post-load sync
FailbackMOLT ReplicatorReplicate changes from CockroachDB back to the source database.Rollback scenarios

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Bulk load

For migrations that tolerate downtime, use MOLT Fetch in data-load mode to perform a one-time bulk load of source data into CockroachDB.

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Migrations with minimal downtime

To minimize downtime during migration, use MOLT Fetch for initial data loading followed by MOLT Replicator for continuous replication. Instead of loading all data during a planned downtime window, you can run an initial load followed by continuous replication. Writes are paused only briefly to allow replication to drain before the final cutover. The duration of this pause depends on the volume of write traffic and the replication lag between the source and CockroachDB.

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Recovery and rollback strategies

If the migration is interrupted or cutover must be aborted, MOLT Replicator provides safe recovery options:
  • Resume replication: Resume a previously interrupted replication stream
  • Failback mode: Reverse the migration, synchronizing changes from CockroachDB back to the original source. This ensures data consistency on the source so that you can retry the migration later.

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Next steps

PostgreSQL Migration

Migrate from PostgreSQL to CockroachDB

MySQL Migration

Migrate from MySQL to CockroachDB

Migration Strategy

Plan your migration approach

Schema Design

Best practices for schema design

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