elasticsearch/docs/reference/cluster/tasks.asciidoc

[[tasks]]
=== Task Management API

beta[The Task Management API is new and should still be considered a beta feature.  The API may change in ways that are not backwards compatible]

Returns information about the tasks currently executing in the cluster.

[[tasks-api-request]]
==== {api-request-title}

`GET /_tasks` +

`GET /_tasks/<task_id>`


[[tasks-api-desc]]
==== {api-description-title}

The task management API allows to retrieve information about the tasks currently
executing on one or more nodes in the cluster.


[[tasks-api-path-params]]
==== {api-path-parms-title}

`<task_id>`::
    (Optional, string) The ID of the task to return (`node_id:task_number`).


[[tasks-api-query-params]]
==== {api-query-parms-title}

include::{docdir}/rest-api/common-parms.asciidoc[tag=timeoutparms]

`wait_for_completion`::
    (Optional, boolean) If `true`, it waits for the matching tasks to complete. 
    Defaults to `false`.


    
[[tasks-api-response-codes]]
==== {api-response-codes-title}

`404` (Missing resources)::
    If `{task_id}` is specified but not found, this code indicates that there 
    are no resources that match the request.


[[tasks-api-examples]]
==== {api-examples-title}

[source,console]
--------------------------------------------------
GET _tasks <1>
GET _tasks?nodes=nodeId1,nodeId2 <2>
GET _tasks?nodes=nodeId1,nodeId2&actions=cluster:* <3>
--------------------------------------------------
// TEST[skip:No tasks to retrieve]

<1> Retrieves all tasks currently running on all nodes in the cluster.
<2> Retrieves all tasks running on nodes `nodeId1` and `nodeId2`.  See <<cluster-nodes>> for more info about how to select individual nodes.
<3> Retrieves all cluster-related tasks running on nodes `nodeId1` and `nodeId2`.

The API returns the following result:

[source,console-result]
--------------------------------------------------
{
  "nodes" : {
    "oTUltX4IQMOUUVeiohTt8A" : {
      "name" : "H5dfFeA",
      "transport_address" : "127.0.0.1:9300",
      "host" : "127.0.0.1",
      "ip" : "127.0.0.1:9300",
      "tasks" : {
        "oTUltX4IQMOUUVeiohTt8A:124" : {
          "node" : "oTUltX4IQMOUUVeiohTt8A",
          "id" : 124,
          "type" : "direct",
          "action" : "cluster:monitor/tasks/lists[n]",
          "start_time_in_millis" : 1458585884904,
          "running_time_in_nanos" : 47402,
          "cancellable" : false,
          "parent_task_id" : "oTUltX4IQMOUUVeiohTt8A:123"
        },
        "oTUltX4IQMOUUVeiohTt8A:123" : {
          "node" : "oTUltX4IQMOUUVeiohTt8A",
          "id" : 123,
          "type" : "transport",
          "action" : "cluster:monitor/tasks/lists",
          "start_time_in_millis" : 1458585884904,
          "running_time_in_nanos" : 236042,
          "cancellable" : false
        }
      }
    }
  }
}
--------------------------------------------------

===== Retrieve information from a particular task

It is also possible to retrieve information for a particular task. The following 
example retrieves information about task `oTUltX4IQMOUUVeiohTt8A:124`:

[source,console]
--------------------------------------------------
GET _tasks/oTUltX4IQMOUUVeiohTt8A:124
--------------------------------------------------
// TEST[catch:missing]

If the task isn't found, the API returns a 404.

To retrieve all children of a particular task:

[source,console]
--------------------------------------------------
GET _tasks?parent_task_id=oTUltX4IQMOUUVeiohTt8A:123
--------------------------------------------------

If the parent isn't found, the API does not return a 404.


===== Get more information about tasks

You can also use the `detailed` request parameter to get more information about
the running tasks. This is useful for telling one task from another but is more
costly to execute. For example, fetching all searches using the `detailed`
request parameter:

[source,console]
--------------------------------------------------
GET _tasks?actions=*search&detailed
--------------------------------------------------
// TEST[skip:No tasks to retrieve]

The API returns the following result:

[source,console-result]
--------------------------------------------------
{
  "nodes" : {
    "oTUltX4IQMOUUVeiohTt8A" : {
      "name" : "H5dfFeA",
      "transport_address" : "127.0.0.1:9300",
      "host" : "127.0.0.1",
      "ip" : "127.0.0.1:9300",
      "tasks" : {
        "oTUltX4IQMOUUVeiohTt8A:464" : {
          "node" : "oTUltX4IQMOUUVeiohTt8A",
          "id" : 464,
          "type" : "transport",
          "action" : "indices:data/read/search",
          "description" : "indices[test], types[test], search_type[QUERY_THEN_FETCH], source[{\"query\":...}]",
          "start_time_in_millis" : 1483478610008,
          "running_time_in_nanos" : 13991383,
          "cancellable" : true
        }
      }
    }
  }
}
--------------------------------------------------

The new `description` field contains human readable text that identifies the
particular request that the task is performing such as identifying the search
request being performed by a search task like the example above. Other kinds of
task have different descriptions, like <<docs-reindex,`_reindex`>> which
has the search and the destination, or <<docs-bulk,`_bulk`>> which just has the
number of requests and the destination indices. Many requests will only have an
empty description because more detailed information about the request is not
easily available or particularly helpful in identifying the request.

[IMPORTANT]
==============================

`_tasks` requests with `detailed` may also return a `status`. This is a report
of the internal status of the task. As such its format varies from task to task.
While we try to keep the `status` for a particular task consistent from version
to version this isn't always possible because we sometimes change the
implementation. In that case we might remove fields from the `status` for a
particular request so any parsing you do of the status might break in minor
releases.

==============================


===== Wait for completion

The task API can also be used to wait for completion of a particular task. The
following call will block for 10 seconds or until the task with id
`oTUltX4IQMOUUVeiohTt8A:12345` is completed.

[source,console]
--------------------------------------------------
GET _tasks/oTUltX4IQMOUUVeiohTt8A:12345?wait_for_completion=true&timeout=10s
--------------------------------------------------
// TEST[catch:missing]

You can also wait for all tasks for certain action types to finish. This command 
will wait for all `reindex` tasks to finish:

[source,console]
--------------------------------------------------
GET _tasks?actions=*reindex&wait_for_completion=true&timeout=10s
--------------------------------------------------


===== Listing tasks by using _cat

Tasks can be also listed using _cat version of the list tasks command, which
accepts the same arguments as the standard list tasks command.

[source,console]
--------------------------------------------------
GET _cat/tasks
GET _cat/tasks?detailed
--------------------------------------------------

[[task-cancellation]]
===== Task Cancellation

If a long-running task supports cancellation, it can be cancelled with the cancel 
tasks API. The following example cancels task `oTUltX4IQMOUUVeiohTt8A:12345`:

[source,console]
--------------------------------------------------
POST _tasks/oTUltX4IQMOUUVeiohTt8A:12345/_cancel
--------------------------------------------------

The task cancellation command supports the same task selection parameters as the 
list tasks command, so multiple tasks can be cancelled at the same time. For 
example, the following command will cancel all reindex tasks running on the 
nodes `nodeId1` and `nodeId2`.

[source,console]
--------------------------------------------------
POST _tasks/_cancel?nodes=nodeId1,nodeId2&actions=*reindex
--------------------------------------------------

===== Task Grouping

The task lists returned by task API commands can be grouped either by nodes 
(default) or by parent tasks using the `group_by` parameter. The following 
command will change the grouping to parent tasks:

[source,console]
--------------------------------------------------
GET _tasks?group_by=parents
--------------------------------------------------

The grouping can be disabled by specifying `none` as a `group_by` parameter:

[source,console]
--------------------------------------------------
GET _tasks?group_by=none
--------------------------------------------------


===== Identifying running tasks

The `X-Opaque-Id` header, when provided on the HTTP request header, is going to 
be returned as a header in the response as well as in the `headers` field for in 
the task information. This allows to track certain calls, or associate certain 
tasks with a the client that started them:

[source,sh]
--------------------------------------------------
curl -i -H "X-Opaque-Id: 123456" "http://localhost:9200/_tasks?group_by=parents"
--------------------------------------------------
//NOTCONSOLE

The API returns the following result:

[source,js]
--------------------------------------------------
HTTP/1.1 200 OK
X-Opaque-Id: 123456 <1>
content-type: application/json; charset=UTF-8
content-length: 831

{
  "tasks" : {
    "u5lcZHqcQhu-rUoFaqDphA:45" : {
      "node" : "u5lcZHqcQhu-rUoFaqDphA",
      "id" : 45,
      "type" : "transport",
      "action" : "cluster:monitor/tasks/lists",
      "start_time_in_millis" : 1513823752749,
      "running_time_in_nanos" : 293139,
      "cancellable" : false,
      "headers" : {
        "X-Opaque-Id" : "123456" <2>
      },
      "children" : [
        {
          "node" : "u5lcZHqcQhu-rUoFaqDphA",
          "id" : 46,
          "type" : "direct",
          "action" : "cluster:monitor/tasks/lists[n]",
          "start_time_in_millis" : 1513823752750,
          "running_time_in_nanos" : 92133,
          "cancellable" : false,
          "parent_task_id" : "u5lcZHqcQhu-rUoFaqDphA:45",
          "headers" : {
            "X-Opaque-Id" : "123456" <3>
          }
        }
      ]
    }
  }
}
--------------------------------------------------
//NOTCONSOLE
<1> id as a part of the response header
<2> id for the tasks that was initiated by the REST request
<3> the child task of the task initiated by the REST request