> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ocient.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Monitor Segment Group Transfers

export const Ocient = "Ocient®";

You can perform segment group transfers in the {Ocient} System. Use the data in the `sys.segment_group_transfers` system catalog table to monitor this activity.

## Segments, Segment Groups, and Segment Group Transfers

A segment is the primary storage unit. Individual segments combine together to form segment groups. For details, see [Core Elements of an Ocient System](/core-elements-of-an-ocient-system).

In a system that has multiple storage clusters, the Ocient System might experience a data imbalance between clusters. In this case, you might need to transfer segment group ownership between clusters. Transferring segment groups enables you to transfer the physically stored segments between clusters. During or after the segment group transfer, you can monitor the activity using the `sys.segment_group_transfers` system catalog table.

## Segment Group Transfers System Catalog Table

The database contains the system catalog table named `sys.segment_group_transfers` with these columns:

* `id` — A Universally Unique IDentifier (UUID) that represents the transfer identifier.
* `src_cluster_id`  — The UUID of the source cluster.
* `dst_cluster_id`  — The UUID of the destination cluster.
* `status`  — The current status of the transfer.
  * `ACTIVE`  — The transfer is ongoing.
  * `COMPLETE`  — The transfer is complete and the segment groups are owned by the destination cluster.
  * `FAILED`  — The transfer is not complete and the segment groups are owned by the source cluster. A transfer can be in this state due to an error that prevented the system from transferring segment groups or due to a canceled transfer.
* `segment_group_ids`  — An array of uint64 segment group identifiers.
* `src_committed_osn`  — The ownership sequence number (OSN) where the source cluster no longer returns the segment groups in the transfer for queries.
* `dst_committed_osn`  — The OSN where the destination cluster added the segment groups.  The destination cluster does not return the segment groups for queries unless the query uses at least the `src_committed_osn` value for the OSN of the source cluster.

The database removes segment group transfers from the system upon completion.

## Related Links

[System Catalog](/system-catalog)