[role="xpack"]
[testenv="basic"]
[[start-transform]]
=== Start {transform} API

[subs="attributes"]
++++
<titleabbrev>Start {transform}</titleabbrev>
++++

Starts one or more {transforms}.

[[start-transform-request]]
==== {api-request-title}

`POST _transform/<transform_id>/_start`

[[start-transform-prereqs]]
==== {api-prereq-title}

If the {es} {security-features} are enabled, you must have the following 
built-in roles and privileges:

* `manage_transform`
* source index: `view_index_metadata`  

For more information, see <<security-privileges>> and <<built-in-roles>>.


[[start-transform-desc]]
==== {api-description-title}

When you start a {transform}, it creates the destination index if it
does not already exist. The `number_of_shards` is set to `1` and the
`auto_expand_replicas` is set to `0-1`.

The {transform} deduces the mapping definitions from the source indices. For
scripted fields, it uses <<dynamic-mapping,dynamic mappings>>. If a field in the
destination index is created by `scripted_metric` or `bucket_script`
aggregations, the {transform} uses dynamic mappings unless a template exists or
the destination index already exists. Mapping definitions in the destination
index take precedence over dynamic mappings and templates.

When the {transform} starts, a series of validations occur to ensure
its success. If you deferred validation when you created the
{transform}, they occur when you start the {transform}--with the
exception of privilege checks. When {es} {security-features} are enabled, the
{transform} remembers which roles the user that created it had at the
time of creation and uses those same roles. If those roles do not have the
required privileges on the source and destination indices, the
{transform} fails when it attempts unauthorized operations.

[[start-transform-path-parms]]
==== {api-path-parms-title}

`<transform_id>`::
(Required, string)
include::{docdir}/rest-api/common-parms.asciidoc[tag=transform-id]

[[start-transform-example]]
==== {api-examples-title}

[source,console]
--------------------------------------------------
POST _transform/ecommerce_transform/_start
--------------------------------------------------
// TEST[skip:set up kibana samples]

When the {transform} starts, you receive the following results:

[source,console-result]
----
{
  "acknowledged" : true
}
----