> ## Documentation Index
> Fetch the complete documentation index at: https://cockroachlabs.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.
# Delta Migration
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A *Delta Migration* uses an initial data load, followed by continuous replication, to migrate data to CockroachDB. In this approach, you migrate most application data to the target using MOLT Fetch **before** stopping application traffic to the source database. You then use MOLT Replicator to keep the target database in sync with any changes in the source database (the migration *delta*), before finally halting traffic to the source and cutting over to the target after schema finalization and data verification.
* All source data is migrated to the target at once.
* This approach utilizes continuous replication.
* Failback replication is supported, though this example will not use it. See Phased Delta Migration with Failback Replication for an example of a migration that uses failback replication.
This approach is best for production environments that need to minimize system downtime.
This page describes an example scenario. While the commands provided can be copy-and-pasted, they may need to be altered or reconsidered to suit the needs of your specific environment.
## Example scenario
You have a small (300 GB) database that provides the data store for a web application. You want to migrate the entirety of this database to a new CockroachDB cluster. Business cannot accommodate a full maintenance window, but it can accommodate a brief (\<60 second) halt in traffic.
The application runs on a Kubernetes cluster.
**Estimated system downtime:** 3-5 minutes.
## Step-by-step walkthroughs
The following walkthroughs demonstrate how to use the MOLT tools to perform this migration for each supported source database:
* Delta Migration from PostgreSQL
* Delta Migration from MySQL
* Delta Migration from Oracle
For CockroachDB-to-CockroachDB migrations, contact your account team for guidance.
## See also
* Migration Overview
* Migration Considerations
* Phased Bulk Load Migration
* MOLT Fetch
* MOLT Verify