Docs Menu
Docs Home
/
MongoDB Cluster-to-Cluster Sync
/
Reference
/
Beta Program

A->B->C Migrations

On this page

  • Syntax
  • Behavior
  • Cluster B Size
  • Migration Name
  • Verification
  • Example
  • Learn More

Important

Cluster-to-Cluster Sync Beta Program

This feature is only available in mongosync beta. To learn more, see Cluster-to-Cluster Sync Beta Program.

Starting in mongosync beta 1.8, you can perform A->B->C migrations. A->B->C migrations allow you to perform two consecutive migrations, where the destination cluster of the first migration acts as the source cluster for the second migration.

Syntax

To perform an A->B->C migration, run the following commands when starting mongosync:

./bin/mongosync \
      --cluster0 <cluster-A-connection-string> \
      --cluster1 <cluster-B-connection-string> \
      --migrationName <string>
./bin/mongosync \
      --cluster0 <cluster-B-connection-string> \
      --cluster1 <cluster-C-connection-string> \
      --migrationName <string>

To start the sync operation between the source and destination clusters, see Synchronize Data Between Clusters.

Behavior

The first migration (A->B) must finish committing before the second migration (B->C) starts committing.

Warning

If the second migration starts committing before the first migration finishes, you may experience data loss.

Before you use any experimental mongosync beta features, review the Cluster-to-Cluster Sync Beta Program Disclaimer.

For better performance, ensure that the first migration (A->B) reaches change event application before the second migration (B->C) starts. To see if a migration reached change event application, check the info field in the progress response document.

Cluster B Size

Writes from cluster A and reads from cluster C can result in heavy loads for cluster B. Ensure that cluster B is sufficiently sized and can handle simultaneous read and write loads.

Migration Name

The migrationName string can contain up to 44 alphanumeric and underscore characters. migrationName is appended to the string "mongosync_internal_" to set the migration metadata database name.

For example, if you set migrationName to "cluster_27000_to_cluster_35000_sync", the resulting mongosync metadata database name is "mongosync_internal_cluster_27000_to_cluster_35000_sync".

Verification

A->B->C Migrations is not compatible with the Embedded Verifier. The /start command returns an error if you enable both the verifier and A->B->C Migrations.

For more information, see Verify Data Transfer.

Example

The following example performs two consecutive migrations that:

  1. Connect a source cluster running on port 27000 with a destination cluster running on port 27001.

  2. Use the destination cluster running on port 27001 as a source cluster for the second migration.

  3. Connect the source cluster on port 27001 with a destination cluster running on port 27002.

The command also sets --migrationName to describe the operations and store migration metadata for each sync.

./bin/mongosync \
      --cluster0 "mongodb://localhost:27000" \
      --cluster1 "mongodb://localhost:27001" \
      --migrationName "cluster_27000_to_cluster_27001_sync"
./bin/mongosync \
      --cluster0 "mongodb://localhost:27001" \
      --cluster1 "mongodb://localhost:27002" \
      --migrationName "cluster_27001_to_cluster_27002_sync"

Learn More

Back

Beta Program

Next

Many-To-One Migrations