Transfers in DoubleCloud

DoubleCloud Transfer provides a convenient way to transfer data between DBMSes, object stores, and message brokers. Using Transfer reduces your migration period and minimizes downtime when switching to a new database. It can create a permanent replica of the database and automatically transfer the database schema from the source to the target.

Transfer creates a pipeline that connects source and target endpoints.

Types

There are three types of transfers available at DoubleCloud:

Snapshot moves a snapshot of the source to the target once.
Periodic snapshot repeatedly moves a snapshot of the source to the target.
Replication continuously receives changes from the source and applies them to the target while the initial data synchronization isn't performed.
Snapshot and replication transfers the current state of the source and then keeps it updated if changes occur.

Transfer life cycles

Snapshot

The Snapshot type transfers the state of the source database to the target on a single occasion. This transfer type doesn't constantly update the target database: changes that occur on the source after transfer is completed won't automatically copied to the target.

This transfer type is useful for the tasks with no writing load on the source, or when there is no need for constant target database updates.

When the transfer is ready, its status switches to Snapshotting throughout the data migration process from source to target. Upon completion, the transfer deactivates automatically, and acquires the Done status.

Periodic snapshot

This type is the same as the Snapshot type but runs a transfer at the specified interval.

Replication

The Replication type transfers changes from the source to the target without copying the complete dataset - only the data schema is transferred upon activation.

After the user activates the transfer, its status permanently changes to Running. All the changes that occur at the source are automatically transmitted to the target.

Snapshot and replication

The Snapshot and replication type combines the Snapshot and Replication transfers: first, the service transfers all the source data to the target, and then it's automatically updated.

After activation, the status of the transfer changes to Snapshotting. This status will persist until all the data from the source is transferred to the target. Then the status will switch to Running. This means all the changes that occur on the source will be automatically transferred to the target.

Transfer statuses

The following table contains all the Transfer statuses:

Status	Description
`Created`	Assigned to a transfer after creation.
`Creating`	Assigned to a transfer after activation. At this stage, the service checks the connection to the source and target endpoints and allocates the resources necessary for the transfer.
`Running`	Assigned to Replication type transfers after successful activation.
`Snapshotting`	Assigned to Snapshot type transfers after successful activation.
`Stopping`	Assigned to a transfer undergoing deactivation. At this stage, the service performs the actions necessary to disconnect from the source and target endpoints properly.
`Stopped`	Assigned to a transfer after deactivation is complete.
`Done`	Assigned to transfers that have completed the data migration process.
`Error`	Assigned to a transfer if any issues occur. Errors can be caused by operations on a source and/or target endpoint. Use logs to find more information about the error.