Use the Remote Store Stats API to monitor shard-level remote-backed storage performance.
Metrics returned from this API only relate to indexes stored on remote-backed nodes. For an aggregated output on an index at the node or cluster level, use the [Index Stats]({{site.url}}{{site.baseurl}}/api-reference/index-apis/stats/), [Nodes Stats]({{site.url}}{{site.baseurl}}/api-reference/nodes-apis/nodes-stats/), or [Cluster Stats]({{site.url}}{{site.baseurl}}/api-reference/cluster-api/cluster-stats/) API.
The response body of the Remote Store Stats API is split into three categories:
*`routing` : Contains information related to the shard’s routing
*`segment` : Contains statistics related to segment transfers from remote-backed storage
*`translog` : Contains statistics related to translog transfers from remote-backed storage
#### routing
The `routing` object contains the following fields.
|Field |Description |
|:--- |:--- |
| `primary` | Denotes whether the shard copy is a primary shard. |
| `node` | The name of the node to which the shard is assigned. |
#### segment
The `segment.upload` object contains the following fields.
|Field |Description |
|:--- |:--- |
| `local_refresh_timestamp_in_millis` | The last successful local refresh timestamp, in milliseconds. |
| `remote_refresh_timestamp_in_millis` | The last successful remote refresh timestamp, in milliseconds. |
| `refresh_time_lag_in_millis` | The amount of time, in milliseconds, that the remote refresh is behind the local refresh. |
| `refresh_lag` | The number of refreshes by which the remote store is lagging behind the local store. |
| `bytes_lag` | The lag, in bytes, between the remote and local stores. |
| `backpressure_rejection_count` | The total number of write rejections issued due to backpressure in the remote store. |
| `consecutive_failure_count` | The number of consecutive remote refresh failures since the last successful refresh. |
| `total_remote_refresh` | The total number of remote refreshes. |
| `total_uploads_in_bytes` | The total number of bytes in all uploads to the remote store. |
| `remote_refresh_size_in_bytes.last_successful` | The size of the data uploaded during the last successful refresh. |
| `remote_refresh_size_in_bytes.moving_avg` | The average size of the data, in bytes, uploaded in the last *N* refreshes. *N* is defined in the `remote_store.moving_average_window_size` setting. For more information, see [Remote segment backpressure](https://opensearch.org/docs/latest/tuning-your-cluster/availability-and-recovery/remote-store/remote-segment-backpressure/). |
| `upload_latency_in_bytes_per_sec.moving_avg` | The average speed of remote segment uploads, in bytes per second, for the last *N* uploads. *N* is defined in the `remote_store.moving_average_window_size` setting. For more information, see [Remote segment backpressure](https://opensearch.org/docs/latest/tuning-your-cluster/availability-and-recovery/remote-store/remote-segment-backpressure/). |
| `remote_refresh_latency_in_millis.moving_avg` | The average amount of time, in milliseconds, taken by a single remote refresh during the last *N* remote refreshes. *N* is defined in the `remote_store.moving_average_window_size` setting. For more information, see [Remote segment backpressure](https://opensearch.org/docs/latest/tuning-your-cluster/availability-and-recovery/remote-store/remote-segment-backpressure/). |
The `segment.download` object contains the following fields.
|Field |Description |
|:--- |:--- |
| `last_sync_timestamp`| The timestamp, in milliseconds, since the last successful segment file download from remote-backed storage. |
| `total_download_size.started_bytes` | The total number of bytes of segment files actively being downloaded from remote-backed storage. |
| `total_download_size.succeeded_bytes` | The total number of bytes of segment files successfully downloaded from remote-backed storage. |
| `total_download_size.failed_bytes` | The total number of bytes of segment files that failed to download from remote-back storage. |
| `download_size_in_bytes.last_successful` | The size, in bytes, of the last segment file successfully downloaded from remote-backed storage. |
| `download_size_in_bytes.moving_avg` | The average size of segment data, in bytes, downloaded in the last 20 downloads. |
| `download_speed_in_bytes_per_sec.moving_avg` | The average download speed, in bytes per second, of the last 20 downloads. |
#### translog
The `translog.upload` object contains the following fields.
| `last_successful_upload_timestamp`| The timestamp, in milliseconds, since the last translog file successfully uploaded to remote-backed storage. |
| `total_uploads.started` | The total number of attempted translog upload syncs to remote-backed storage. |
| `total_uploads.failed` | The total number of failed translog upload syncs to remote-backed storage. |
| `total_uploads.succeeded` | The total number of successful translog upload syncs to remote-backed storage. |
| `total_upload_size.started_bytes` | The total number of bytes of translog files actively being downloaded from remote-backed storage. |
| `total_upload_size.succeeded_bytes` | The total number of bytes of translog files successfully uploaded to remote-backed storage. |
|`total_upload_size.failed_bytes` | The total number of bytes of translog files that failed to upload to remote-backed storage. |
| `total_upload_time_in_millis` | The total amount of time spent, in milliseconds, uploading translog files to remote-backed storage. |
| `upload_size_in_bytes.moving_avg` | The average size of translog data, in bytes, uploaded in the last *N* downloads. *N* is defined in the `remote_store.moving_average_window_size` setting. |
| `upload_speed_in_bytes_per_sec.moving_avg` | The average speed of translog uploads, in bytes per second, for the last *N* uploads. *N* is defined in the `remote_store.moving_average_window_size` setting. |
| `upload_time_in_millis.moving_avg` | The average amount of time taken by a single translog upload, in milliseconds, since the last *N* uploads. *N* is defined in the `remote_store.moving_average_window_size` setting. |
The `translog.download` object contains the following fields.
|Field |Description |
|:--- |:--- |
| `last_successful_download_timestamp` | The timestamp, in milliseconds, since the last translog file successfully uploaded to remote-backed storage. |
| `total_downloads.succeeded` | The total number of successful translog download syncs from remote-backed storage. |
| `total_download_size.succeeded_bytes` | The total number of bytes of translog files successfully uploaded from remote-backed storage. |
| `total_download_time_in_millis` | The total amount of time spent, in milliseconds, downloading translog files from remote-backed storage. |
| `download_size_in_bytes.moving_avg` | The average size of translog data, in bytes, downloaded in the last *N* downloads. *N* is defined in the `remote_store.moving_average_window_size` setting. |
| `download_speed_in_bytes_per_sec.moving_avg` | The average speed of translog downloads, in bytes per second, for the last *N* uploads. *N* is defined in the `remote_store.moving_average_window_size` setting. |
| `download_time_in_millis.moving_avg` | The average amount of time taken by a single translog download, in milliseconds, since the last *N* uploads. *N* is defined in the `remote_store.moving_average_window_size` setting. |
If you want to fetch only shards present on the node serving a Remote Store Stats API request, set the `local` query parameter to `true`, as shown in the following example request:
