[role="xpack"]
[[data-streams-change-mappings-and-settings]]
== Change mappings and settings for a data stream

Each data stream has a <<create-a-data-stream-template,matching index
template>>. Mappings and index settings from this template are applied to new
backing indices created for the stream. This includes the stream's first
backing index, which is auto-generated when the stream is created.

Before creating a data stream, we recommend you carefully consider which
mappings and settings to include in this template.

If you later need to change the mappings or settings for a data stream, you have
a few options:

* <<add-new-field-mapping-to-a-data-stream>>
* <<change-existing-field-mapping-in-a-data-stream>>
* <<change-dynamic-index-setting-for-a-data-stream>>
* <<change-static-index-setting-for-a-data-stream>>

TIP: If your changes include modifications to existing field mappings or
<<index-modules-settings,static index settings>>, a reindex is often required to
apply the changes to a data stream's backing indices. If you are already
performing a reindex, you can use the same process to add new field
mappings and change <<index-modules-settings,dynamic index settings>>. See
<<data-streams-use-reindex-to-change-mappings-settings>>.

////
[source,console]
----
PUT /_ilm/policy/my-data-stream-policy
{
  "policy": {
    "phases": {
      "hot": {
        "actions": {
          "rollover": {
            "max_size": "25GB"
          }
        }
      },
      "delete": {
        "min_age": "30d",
        "actions": {
          "delete": {}
        }
      }
    }
  }
}

PUT /_index_template/my-data-stream-template
{
  "index_patterns": [ "my-data-stream*" ],
  "data_stream": { }
}

PUT /_index_template/new-data-stream-template
{
  "index_patterns": [ "new-data-stream*" ],
  "data_stream": { }
}

PUT /_data_stream/my-data-stream

POST /my-data-stream/_rollover/

PUT /_data_stream/new-data-stream
----
// TESTSETUP

[source,console]
----
DELETE /_data_stream/*

DELETE /_index_template/*

DELETE /_ilm/policy/my-data-stream-policy
----
// TEARDOWN
////

[discrete]
[[add-new-field-mapping-to-a-data-stream]]
=== Add a new field mapping to a data stream

To add a mapping for a new field to a data stream, following these steps:

. Update the index template used by the data stream. This ensures the new
field mapping is added to future backing indices created for the stream.
+
--
For example, `my-data-stream-template` is an existing index template used by
`my-data-stream`.

The following <<indices-templates,put index template>> request adds a mapping
for a new field, `message`, to the template.

[source,console]
----
PUT /_index_template/my-data-stream-template
{
  "index_patterns": [ "my-data-stream*" ],
  "data_stream": { },
  "priority": 200,
  "template": {
    "mappings": {
      "properties": {
        "message": {                              <1>
          "type": "text"
        }
      }
    }
  }
}
----
<1> Adds a mapping for the new `message` field.
--

. Use the <<indices-put-mapping,put mapping API>> to add the new field mapping
to the data stream. By default, this adds the mapping to the stream's existing
backing indices, including the write index.
+
--
The following put mapping API request adds the new `message` field mapping to
`my-data-stream`.

[source,console]
----
PUT /my-data-stream/_mapping
{
  "properties": {
    "message": {
      "type": "text"
    }
  }
}
----
--
+
To add the mapping only to the stream's write index, set the put mapping API's
`write_index_only` query parameter to `true`.
+
--
The following put mapping request adds the new `message` field mapping only to
`my-data-stream`'s write index. The new field mapping is not added to
the stream's other backing indices.

[source,console]
----
PUT /my-data-stream/_mapping?write_index_only=true
{
  "properties": {
    "message": {
      "type": "text"
    }
  }
}
----
--

[discrete]
[[change-existing-field-mapping-in-a-data-stream]]
=== Change an existing field mapping in a data stream

The documentation for each <<mapping-params,mapping parameter>> indicates
whether you can update it for an existing field using the
<<indices-put-mapping,put mapping API>>. To update these parameters for an
existing field, follow these steps:

. Update the index template used by the data stream. This ensures the updated
field mapping is added to future backing indices created for the stream.
+
--
For example, `my-data-stream-template` is an existing index template used by
`my-data-stream`.

The following <<indices-templates,put index template>> request changes the
argument for the `host.ip` field's <<ignore-malformed,`ignore_malformed`>>
mapping parameter to `true`.

[source,console]
----
PUT /_index_template/my-data-stream-template
{
  "index_patterns": [ "my-data-stream*" ],
  "data_stream": { },
  "priority": 200,
  "template": {
    "mappings": {
      "properties": {
        "host": {
          "properties": {
            "ip": {
              "type": "ip",
              "ignore_malformed": true            <1>
            }
          }
        }
      }
    }
  }
}
----
<1> Changes the `host.ip` field's `ignore_malformed` value to `true`.
--

. Use the <<indices-put-mapping,put mapping API>> to apply the mapping changes
to the data stream. By default, this applies the changes to the stream's
existing backing indices, including the write index.
+
--
The following <<indices-put-mapping,put mapping API>> request targets
`my-data-stream`. The request changes the argument for the `host.ip`
field's `ignore_malformed` mapping parameter to `true`.

[source,console]
----
PUT /my-data-stream/_mapping
{
  "properties": {
    "host": {
      "properties": {
        "ip": {
          "type": "ip",
          "ignore_malformed": true
        }
      }
    }
  }
}
----
--
+
To apply the mapping changes only to the stream's write index, set the put
mapping API's `write_index_only` query parameter to `true`.
+
--
The following put mapping request changes the `host.ip` field's mapping only for
`my-data-stream`'s write index. The change is not applied to the
stream's other backing indices.

[source,console]
----
PUT /my-data-stream/_mapping?write_index_only=true
{
  "properties": {
    "host": {
      "properties": {
        "ip": {
          "type": "ip",
          "ignore_malformed": true
        }
      }
    }
  }
}
----
--

Except for supported mapping parameters, we don't recommend you change the
mapping or field data type of existing fields, even in a data stream's matching
index template or its backing indices. Changing the mapping of an existing
field could invalidate any data that’s already indexed.

If you need to change the mapping of an existing field, create a new
data stream and reindex your data into it. See
<<data-streams-use-reindex-to-change-mappings-settings>>.

[discrete]
[[change-dynamic-index-setting-for-a-data-stream]]
=== Change a dynamic index setting for a data stream

To change a <<index-modules-settings,dynamic index setting>> for a data stream,
follow these steps:

. Update the index template used by the data stream. This ensures the setting is
applied to future backing indices created for the stream.
+
--
For example, `my-data-stream-template` is an existing index template used by
`my-data-stream`.

The following <<indices-templates,put index template>> request changes the
template's `index.refresh_interval` index setting to `30s` (30 seconds).

[source,console]
----
PUT /_index_template/my-data-stream-template
{
  "index_patterns": [ "my-data-stream*" ],
  "data_stream": { },
  "priority": 200,
  "template": {
    "settings": {
      "index.refresh_interval": "30s"             <1>
    }
  }
}
----
<1> Changes the `index.refresh_interval` setting to `30s` (30 seconds).
--

. Use the <<indices-update-settings,update index settings API>> to update the
index setting for the data stream. By default, this applies the setting to
the stream's existing backing indices, including the write index.
+
--
The following update index settings API request updates the
`index.refresh_interval` setting for `my-data-stream`.

[source,console]
----
PUT /my-data-stream/_settings
{
  "index": {
    "refresh_interval": "30s"
  }
}
----
--

[discrete]
[[change-static-index-setting-for-a-data-stream]]
=== Change a static index setting for a data stream

<<index-modules-settings,Static index settings>> can only be set when a backing
index is created. You cannot update static index settings using the
<<indices-update-settings,update index settings API>>.

To apply a new static setting to future backing indices, update the index
template used by the data stream. The setting is automatically applied to any
backing index created after the update.

For example, `my-data-stream-template` is an existing index template used by
`my-data-stream`.

The following <<indices-templates,put index template API>> requests adds new
`sort.field` and `sort.order index` settings to the template.

[source,console]
----
PUT /_index_template/my-data-stream-template
{
  "index_patterns": [ "my-data-stream*" ],
  "data_stream": { },
  "priority": 200,
  "template": {
    "settings": {
      "sort.field": [ "@timestamp"],             <1>
      "sort.order": [ "desc"]                    <2>
    }
  }
}
----
<1> Adds the `sort.field` index setting.
<2> Adds the `sort.order` index setting.

If wanted, you can <<manually-roll-over-a-data-stream,roll over the data
stream>> to immediately apply the setting to the data stream’s write index. This
affects any new data added to the stream after the rollover. However, it does
not affect the data stream's existing backing indices or existing data.

To apply static setting changes to existing backing indices, you must create a
new data stream and reindex your data into it. See
<<data-streams-use-reindex-to-change-mappings-settings>>.

[discrete]
[[data-streams-use-reindex-to-change-mappings-settings]]
=== Use reindex to change mappings or settings

You can use a reindex to change the mappings or settings of a data stream. This
is often required to change the data type of an existing field or update static
index settings for backing indices.

To reindex a data stream, first create or update an index template so that it
contains the wanted mapping or setting changes. You can then reindex the
existing data stream into a new stream matching the template. This applies the
mapping and setting changes in the template to each document and backing index
added to the new data stream. These changes also affect any future backing
index created by the new stream.

Follow these steps:

. Choose a name or index pattern for a new data stream. This new data
stream will contain data from your existing stream.
+
You can use the resolve index API to check if the name or pattern matches any
existing indices, index aliases, or data streams. If so, you should consider
using another name or pattern.
--
The following resolve index API request checks for any existing indices, index
aliases, or data streams that start with `new-data-stream`. If not, the
`new-data-stream*` index pattern can be used to create a new data stream.

[source,console]
----
GET /_resolve/index/new-data-stream*
----

The API returns the following response, indicating no existing targets match
this pattern.

[source,console-result]
----
{
  "indices": [ ],
  "aliases": [ ],
  "data_streams": [ ]
}
----
// TESTRESPONSE[s/"data_streams": \[ \]/"data_streams": $body.data_streams/]
--

. Create or update an index template. This template should contain the
mappings and settings you'd like to apply to the new data stream's backing
indices.
+
This index template must meet the
<<create-a-data-stream-template,requirements for a data stream template>>. It
should also contain your previously chosen name or index pattern in the
`index_patterns` property.
+
TIP: If you are only adding or changing a few things, we recommend you create a
new template by copying an existing one and modifying it as needed.
+
--
For example, `my-data-stream-template` is an existing index template used by
`my-data-stream`.

The following <<indices-templates,put index template API>> request creates a new
index template, `new-data-stream-template`. `new-data-stream-template`
uses `my-data-stream-template` as its basis, with the following
changes:

* The index pattern in `index_patterns` matches any index or data stream
  starting with `new-data-stream`.
* The `@timestamp` field mapping uses the `date_nanos` field data type rather
  than the `date` data type.
* The template includes `sort.field` and `sort.order` index settings, which were
  not in the original `my-data-stream-template` template.

[source,console]
----
PUT /_index_template/new-data-stream-template
{
  "index_patterns": [ "new-data-stream*" ],
  "data_stream": { },
  "priority": 200,
  "template": {
    "mappings": {
      "properties": {
        "@timestamp": {
          "type": "date_nanos"                 <1>
        }
      }
    },
    "settings": {
      "sort.field": [ "@timestamp"],          <2>
      "sort.order": [ "desc"]                 <3>
    }
  }
}
----
<1>  Changes the `@timestamp` field mapping to the `date_nanos` field data type.
<2>  Adds the `sort.field` index setting.
<3>  Adds the `sort.order` index setting.
--

. Use the <<indices-create-data-stream,create data stream API>> to manually
create the new data stream. The name of the data stream must match the index
pattern defined in the new template's `index_patterns` property.
+
We do not recommend <<create-a-data-stream,indexing new data
to create this data stream>>. Later, you will reindex older data from an
existing data stream into this new stream. This could result in one or more
backing indices that contains a mix of new and old data.
+
[[data-stream-mix-new-old-data]]
.Mixing new and old data in a data stream
[IMPORTANT]
====
While mixing new and old data is safe, it could interfere with data retention.
If you delete older indices, you could accidentally delete a backing index that
contains both new and old data. To prevent premature data loss, you would need
to retain such a backing index until you are ready to delete its newest data.
====
+
--
The following create data stream API request targets `new-data-stream`, which
matches the index pattern for `new-data-stream-template`.
Because no existing index or data stream uses this name, this request creates
the `new-data-stream` data stream.

[source,console]
----
PUT /_data_stream/new-data-stream
----
// TEST[s/new-data-stream/new-data-stream-two/]
--

. If you do not want to mix new and old data in your new data stream, pause the
indexing of new documents. While mixing old and new data is safe, it could
interfere with data retention. See <<data-stream-mix-new-old-data,Mixing new and
old data in a data stream>>.

. If you use {ilm-init} to <<getting-started-index-lifecycle-management,automate
rollover>>, reduce the {ilm-init} poll interval. This ensures the current write
index doesn’t grow too large while waiting for the rollover check. By default,
{ilm-init} checks rollover conditions every 10 minutes.
+
--
The following <<cluster-update-settings,update cluster settings API>> request
lowers the `indices.lifecycle.poll_interval` setting to `1m` (one minute).

[source,console]
----
PUT /_cluster/settings
{
  "transient": {
    "indices.lifecycle.poll_interval": "1m"
  }
}
----
--

. Reindex your data to the new data stream using an `op_type` of `create`.
+
If you want to partition the data in the order in which it was originally
indexed, you can run separate reindex requests. These reindex requests can use
individual backing indices as the source. You can use the
<<indices-get-data-stream,get data stream API>> to retrieve a list of backing
indices.
+
--
For example, you plan to reindex data from `my-data-stream` into
`new-data-stream`. However, you want to submit a separate reindex request for
each backing index in `my-data-stream`, starting with the oldest backing index.
This preserves the order in which the data was originally indexed.

The following get data stream API request retrieves information about
`my-data-stream`, including a list of its backing indices.

[source,console]
----
GET /_data_stream/my-data-stream
----

The API returns the following response. Note the `indices` property contains an
array of the stream's current backing indices. The first item in the array
contains information about the stream's oldest backing index,
`.ds-my-data-stream-000001`.

[source,console-result]
----
{
  "data_streams": [
    {
      "name": "my-data-stream",
      "timestamp_field": {
        "name": "@timestamp"
      },
      "indices": [
        {
          "index_name": ".ds-my-data-stream-000001",        <1>
          "index_uuid": "Gpdiyq8sRuK9WuthvAdFbw"
        },
        {
          "index_name": ".ds-my-data-stream-000002",
          "index_uuid": "_eEfRrFHS9OyhqWntkgHAQ"
        }
      ],
      "generation": 2,
      "status": "GREEN",
      "template": "my-data-stream-template"
    }
  ]
}
----
// TESTRESPONSE[s/"index_uuid": "Gpdiyq8sRuK9WuthvAdFbw"/"index_uuid": $body.data_streams.0.indices.0.index_uuid/]
// TESTRESPONSE[s/"index_uuid": "_eEfRrFHS9OyhqWntkgHAQ"/"index_uuid": $body.data_streams.0.indices.1.index_uuid/]
// TESTRESPONSE[s/"status": "GREEN"/"status": "YELLOW"/]

<1> First item in the `indices` array for `my-data-stream`. This
item contains information about the stream's oldest backing index,
`.ds-my-data-stream-000001`.

The following <<docs-reindex,reindex API>> request copies documents from
`.ds-my-data-stream-000001` to `new-data-stream`. Note the request's `op_type`
is `create`.

[source,console]
----
POST /_reindex
{
  "source": {
    "index": ".ds-my-data-stream-000001"
  },
  "dest": {
    "index": "new-data-stream",
    "op_type": "create"
  }
}
----
--
+
You can also use a query to reindex only a subset of documents with each
request.
+
--
The following <<docs-reindex,reindex API>> request copies documents from
`my-data-stream` to `new-data-stream`. The request
uses a <<query-dsl-range-query,`range` query>> to only reindex documents with a
timestamp within the last week. Note the request's `op_type` is `create`.

[source,console]
----
POST /_reindex
{
  "source": {
    "index": "my-data-stream",
    "query": {
      "range": {
        "@timestamp": {
          "gte": "now-7d/d",
          "lte": "now/d"
        }
      }
    }
  },
  "dest": {
    "index": "new-data-stream",
    "op_type": "create"
  }
}
----
--

. If you previously changed your {ilm-init} poll interval, change it back to its
original value when reindexing is complete. This prevents unnecessary load on
the master node.
+
--
The following update cluster settings API request resets the
`indices.lifecycle.poll_interval` setting to its default value, 10 minutes.

[source,console]
----
PUT /_cluster/settings
{
  "transient": {
    "indices.lifecycle.poll_interval": null
  }
}
----
--

. Resume indexing using the new data stream. Searches on this stream will now
query your new data and the reindexed data.

. Once you have verified that all reindexed data is available in the new
data stream, you can safely remove the old stream.
+
--
The following <<indices-delete-data-stream,delete data stream API>> request
deletes `my-data-stream`. This request also deletes the stream's
backing indices and any data they contain.

[source,console]
----
DELETE /_data_stream/my-data-stream
----
--
