> For clean Markdown of any page, append .md to the page URL. > For a complete documentation index, see https://ocient.ferndocs.com/llms.txt. > For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://ocient.ferndocs.com/_mcp/server. # Distributed Tasks > Ensure data integrity and performance with rebuild tasks and data checks in Ocient. You can manage distributed tasks in the Ocient® System. These tasks are processes that run in the background of the system to keep it running smoothly and efficiently. These DDL commands create tasks to rebuild damaged or missing segment data and check data integrity. For information about managing these tasks, see [**Manage Distributed Tasks**](/guides/database-administration/manage-distributed-tasks). ## CREATE TASK Launches a new task. To create a rebuild or check disk task, you must be assigned the System Administrator role. **Syntax** ```sql CREATE TASK { | | } ::= [name] TYPE REBUILD [ OPTIONS ('location_type' [, 'location_name' [, ]])] ::= [name] TYPE CHECK_DISK [ OPTIONS ('location_type' [, 'location_name' [, ]])] ::= [name] TYPE REBALANCE ``` ### Rebuilding Segment Task ( `` ) Performing a rebuild segment operation reconstructs data segments by using erasure-coded data in the same segment group. This task allows segments that are in DAMAGED or MISSING status to be restored to full performance. For details about rebuild tasks, see the [**Guide to Rebuilding Segments**](/guides/system-administration/maintenance-overview/guide-to-rebuilding-segments). To create a rebuild segment task, you must have `UPDATE` privileges on the system. Specifying `locationType` of `SYSTEM` means every segment in the system is rebuilt. Alternatively, you can specify individual clusters or nodes by name to rebuild their segments. | **Parameter** | **Data Type** | **Description** | | --------------- | ------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `name` | string | An optional identifier for the task. | | `location_type` | string | Specify the type of location for rebuild from these selections: `'SYSTEM' \| 'CLUSTER'` The value definitions are: `SYSTEM` — Every segment in the system is rebuilt. `CLUSTER` — Only the cluster specified by the `location_name` parameter is rebuilt. | | `location_name` | string | The name of a specific cluster to rebuild. | ### Rebuild Arguments ( `` ) Additional arguments for the rebuild task. These arguments must be in a valid JSON format. All fields are optional. You must specify all arguments in a single JSON object. ```json ::= '{ "node": "node_name", "segment_groups": segment_array, "table_id": "table_id_string" }' ``` | **Parameter** | **Data Type** | **Description** | | ---------------- | ------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `node` | string | If included, this option limits the rebuild process to only rebuild segments on the node specified by `node_name`. If not included, the system rebuilds all segment groups on the cluster or system. | | `segment_groups` | string | If included, this option limits the rebuild process to only the identifiers for the rebuild segment groups specified in the `segment_array`. If not included, the system rebuilds all segment groups on the cluster or system. | | `table_id` | string | If included, this option limits the rebuild process to only rebuild segment groups that belong to the table identifier specified in the `table_id_string`. If not included, the system rebuilds all segment groups on the cluster or system. | ### Checking Disk Task ( `` ) A `CHECK_DISK` task verifies the segments on a node by computing checksums. | **Parameter** | **Data Type** | **Description** | | --------------- | ------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `name` | string | An optional identifier for the task. | | `location_type` | string | The type of location for the check disk task to be performed on. Supported `location_type` values include: `[ 'SYSTEM' \| 'CLUSTER' \| 'NODE' ]` The value definitions are: `SYSTEM` — The task includes all segments. `CLUSTER` — The task covers only a cluster specified by the `location_name`. `NODE` — The task covers only a node specified by the `location_name`. | | `location_name` | string | The specific name of the location where the check disk task is to be performed. This argument is required if the `location_type` argument is set to `'CLUSTER'` or `'NODE'`. | ### **Check Disk Arguments (**``**)** Arguments must be in a valid JSON format. All fields are optional. You must specify all arguments in a single JSON object. ```json ::= '{ "fix": true, "sample": false, "only_unhealthy":false, "storage_ids": ["02c65e30-3651-478e-96bf-9935c1bc8fb4"] }' ``` | **Parameter** | **Data Type** | **Description** | | ---------------- | ------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `fix` | Boolean | If set to `true`, this option modifies the storage cluster state based on the result of the checksum verification. For example, if you set the `fix` option, the system moves a segment that fails the checksum from the `INTACT` state to the `DAMAGED` state. | | `sample` | Boolean | If set to `true`, this option checks only a sample of data in each segment. | | `only_unhealthy` | Boolean | If set to `true`, this option checks only stored segments that are not in the `INTACT` state. | | `storage_ids` | string | This option limits the disk check operation to include only the specified segment storage identifiers. Otherwise, the system checks all segments on the node. | **Examples** Rebuild all segments on a system. ```sql CREATE TASK TYPE rebuild; CREATE TASK TYPE rebuild OPTIONS ('SYSTEM'); ``` Rebuild all segments on a system for a specified table with the table identifier `529a2e9d-d06c-46cd-a93b-624d3bed1c08`. ```sql CREATE TASK TYPE rebuild OPTIONS ('SYSTEM', '{"table_id": "529a2e9d-d06c-46cd-a93b-624d3bed1c08"}'); ``` Rebuild segments on Foundation cluster `my_lts_cluster1`. ```sql CREATE TASK TYPE rebuild OPTIONS ('CLUSTER', 'my_lts_cluster1'); ``` Rebuild segments on a Foundation Node `my_node1`. ```sql CREATE TASK TYPE rebuild OPTIONS ('CLUSTER', 'my_lts_cluster1', '{"node": "my_node1"}'); ``` Rebuild segments on a segment group with the identifier `53`. ```sql CREATE TASK TYPE rebuild OPTIONS ('CLUSTER', 'my_lts_cluster1', '{"segment_groups": [53]}'); ``` Rebuild only the segment in segment group `53` on a Foundation Node `my_node`. ```sql CREATE TASK TYPE rebuild OPTIONS ('CLUSTER', 'my_lts_cluster1', '{"node": "my_node1", "segment_groups": [53]}'); ``` Compute the checksum on all segments on storage node `my_node1`. ```sql CREATE TASK TYPE check_disk OPTIONS ('NODE', 'my_node1'); ``` Compute a checksum on a sample of blocks for each segment on storage cluster `my_lts_cluster1`. ```sql CREATE TASK TYPE check_disk OPTIONS ('CLUSTER', 'my_lts_cluster1', '{"sample": true}'); ``` Compute a checksum on all nodes in the system and modify the state based on the result. ```sql CREATE TASK TYPE check_disk OPTIONS ('SYSTEM', '{"fix": true}'); ``` Compute a checksum for a segment with storage identifier `529a2e9d-d06c-46cd-a93b-624d3bed1c08` on the storage node `my_node1`. ```sql CREATE TASK TYPE check_disk OPTIONS ('NODE', 'my_node1', '{"storage_ids": ["529a2e9d-d06c-46cd-a93b-624d3bed1c08"]}'); ``` ### Rebalance Task (``) Rebalancing evenly distributes data across disks in the system. Run this task if data is not balanced properly across the system, such as after adding additional nodes or drives. For details about rebalancing, see [**Expand and Rebalance System**](/guides/system-administration/maintenance-overview/expand-and-rebalance-system). ## CANCEL TASK Cancels a running task. To cancel a task, you must be assigned the System Administrator role. **Syntax** ```sql CANCEL TASK ('task_name' | 'task_id') ``` | **Parameter** | **Data Type** | **Description** | | ------------- | ------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | `task_name` | string | The name specified on task creation. This applies only if an optional name was created for the task. | | `task_id` | string | The unique identifier for the task in the system tables.  For rebuild tasks, you can find the unique identifier in the [**sys.result_cache**](https://docs.ocient.com/system-catalog#Q_fBp) table. For check disk tasks, you can find the unique identifier in the [**sys.subtasks**](https://docs.ocient.com/system-catalog#UGss3) table. | **Example** Cancel a task named `my_task`. ```sql CANCEL TASK 'my_task'; ``` ## Related Links [**System Catalog**](https://docs.ocient.com/system-catalog) [**Guide to Rebuilding Segments**](/guides/system-administration/maintenance-overview/guide-to-rebuilding-segments)