Many-to-One Migrations

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Syntax

Behavior
Example
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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 Many-to-One migrations. Many-to-One migrations allow you to sync multiple source clusters simultaneously with a destination cluster. For example, you can consolidate data from many small clusters into a central cluster.

Syntax

To sync multiple source clusters with one destination cluster, run the following commands when starting mongosync:

./bin/mongosync \
      --cluster0 <source-A-connection-string> \
      --cluster1 <destination-connection-string> \
      --migrationName <string>
./bin/mongosync \
      --cluster0 <source-B-connection-string> \
      --cluster1 <destination-connection-string> \
      --migrationName <string>

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

Behavior

A namespace is a database_name.collection_name combination. You can only sync namespaces that don't conflict.

For example, consider this scenario:

Two source clusters S1 and S2.
A destination cluster D.
Databases named inventory and sales on both S1 and S2.
Collections named products, orderLines, orderStatus, and orders on both S1 and S2.
You can sync both of these combinations:
- inventory.products and sales.orderStatus on S1 with D.
- inventory.orderLines and sales.orders on S2 with D.
You cannot sync both of these combinations because they conflict:
- inventory.products and inventory.orderLines on S1 with D. If D is initially empty, you can sync S1 with D. inventory.products and inventory.orderLines are copied from S1 to D.
- inventory.products and inventory.orderLines on S2 with D. You cannot sync S2 with D because inventory.products and inventory.orderLines conflict with the namespaces already on D from the scenario in the previous point.

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

Many-to-One Migrations is not compatible with the Embedded Verifier. The /start command returns an error if you enable both the verifier and Many-to-One Migrations.

For more information, see Verify Data Transfer.

Example

The following example connects source clusters running on port 27000 and 27001 with a destination cluster running on port 35000. The command also sets the --migrationName option to describe the operations and store migration metadata for each sync.

./bin/mongosync \
      --cluster0 "mongodb://localhost:27000" \
      --cluster1 "mongodb://localhost:35000" \
      --migrationName "cluster_27000_to_cluster_35000_sync"
./bin/mongosync \
      --cluster0 "mongodb://localhost:27001" \
      --cluster1 "mongodb://localhost:35000" \
      --migrationName "cluster_27001_to_cluster_35000_sync"

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