[[data-streams-change-mappings-and-settings]]
== Change mappings and settings of backing indices
++++
<titleabbrev>Change mappings and settings</titleabbrev>
++++

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. However, if you later need to
change the mappings or settings of a data stream's backing indices, you have a
couple options:

* To apply changes to future backing indices, simply update the index
template used by the data stream. Mapping and setting changes will be
automatically applied to any backing indices created after the update.
+
.*Example*
[%collapsible]
====
`logs_data_stream` is an existing index template used by the
`logs` data stream.

The following <<indices-templates,put index template API>> makes several
changes to the `logs_data_stream` template:

* It changes the `@timestamp` field mapping from the `date` field datatype to
  the `date_nanos` datatype.
* It adds new `sort.field` and `sort.order` index settings.

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

PUT /_index_template/logs_data_stream
{
  "index_patterns": [ "logs*" ],
  "data_stream": {
    "timestamp_field": "@timestamp"
  },
  "template": {
    "mappings": {
      "properties": {
        "@timestamp": {
          "type": "date"
        }
      }
    },
    "settings": {
      "index.lifecycle.name": "logs_policy"
    }
  }
}

PUT /logs/_bulk?refresh
{"create":{"_index" : "logs"}}
{ "@timestamp": "2020-12-08T11:04:05.000Z" }
{"create":{"_index" : "logs"}}
{ "@timestamp": "2020-12-08T11:06:07.000Z" }
{"create":{"_index" : "logs"}}
{ "@timestamp": "2020-12-09T11:07:08.000Z" }
----
////

[source,console]
----
PUT /_index_template/logs_data_stream
{
  "index_patterns": [ "logs*" ],
  "data_stream": {
    "timestamp_field": "@timestamp"
  },
  "template": {
    "mappings": {
      "properties": {
        "@timestamp": {
          "type": "date_nanos"                 <1>
        }
      }
    },
    "settings": {
      "index.lifecycle.name": "logs_policy",
      "sort.field" : [ "@timestamp"],          <2>
      "sort.order" : [ "desc"]                 <3>
    }
  }
}
----
// TEST[continued]

<1>  Changes the `@timestamp` field mapping to the `date_nanos` datatype.
<2>  Adds the `sort.field` index setting.
<3>  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 new mappings and settings to the data stream's
write index. This affects any new data added to the stream after the rollover.
+
.*Example*
[%collapsible]
====
The following <<indices-rollover-index,rollover API>> request rolls over the
`logs` data stream. This creates a new write index with mappings and index
settings from the recently updated `logs_data_stream` template.

[source,console]
----
POST /logs/_rollover/
----
// TEST[continued]
====
+
IMPORTANT: You cannot use these methods to change the mapping of a data stream's
<<create-a-data-stream-template,timestamp field>>. To change the timestamp
field's mapping, you must reindex the data stream. See
<<data-streams-use-reindex-to-change-mappings-settings>>.

* To apply mapping and setting changes to all existing backing indices and
future ones, 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

To change the mappings or settings for every backing index in a data stream, you
must first create or update an index template so that it contains the
changes. You can then reindex the existing data stream into a new one matching
the template. This applies the mapping and setting changes in the template
to each document and backing index of the data stream destination. These changes
also affect any future backing index created by the new stream.

Follow these steps:

. Choose a name or wildcard (`*`) 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.
+
.*Example*
[%collapsible]
====
The following resolve index API request checks for any existing indices, index
aliases, or data streams that start with `new_logs`. If not, the `new_logs*`
wildcard pattern can be used to create a new data stream.

[source,console]
----
GET /_resolve/index/new_logs*
----
// TEST[continued]

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

[source,console-result]
----
{
  "indices" : [ ],
  "aliases" : [ ],
  "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 wildcard 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.
+
.*Example*
[%collapsible]
====
`logs_data_stream` is an existing index template used by the
`logs` data stream.

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

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

[source,console]
----
PUT /_index_template/new_logs_data_stream
{
  "index_patterns": [ "new_logs*" ],
  "data_stream": {
    "timestamp_field": "@timestamp"
  },
  "template": {
    "mappings": {
      "properties": {
        "@timestamp": {
          "type": "date_nanos"                 <1>
        }
      }
    },
    "settings": {
      "index.lifecycle.name": "logs_policy",
      "sort.field" : [ "@timestamp"],          <2>
      "sort.order" : [ "desc"]                 <3>
    }
  }
}
----
// TEST[continued]

<1>  Changes the `@timestamp` field mapping to the `date_nanos` field datatype.
<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 name or
wildcard pattern defined in the new template's `index_patterns` property.
+
We do not recommend <<index-documents-to-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.
====
+
.*Example*
[%collapsible]
====
The following create data stream API request targets `new_logs`, which matches
the wildcard pattern for the `new_logs_data_stream` template. Because no
existing index or data stream uses this name, this request creates the
`new_logs` data stream.

[source,console]
----
PUT /_data_stream/new_logs
----
// TEST[continued]
====

. 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.
+
.*Example*
[%collapsible]
====
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"
  }
}
----
// TEST[continued]

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

DELETE /_data_stream/new_logs

DELETE /_index_template/logs_data_stream

DELETE /_index_template/new_logs_data_stream

DELETE /_ilm/policy/logs_policy
----
// TEST[continued]
////
====

. 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.
+
.*Example*
[%collapsible]
====
You plan to reindex data from the `logs` data stream into the newly created
`new_logs` data stream. However, you want to submit a separate reindex request
for each backing index in the `logs` 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 the `logs`
data stream, including a list of its backing indices.

[source,console]
----
GET /_data_stream/logs
----
// TEST[skip: shard failures]

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

[source,console-result]
----
[
  {
    "name": "logs",
    "timestamp_field": "@timestamp",
    "indices": [
      {
        "index_name": ".ds-logs-000001",
        "index_uuid": "DXAE-xcCQTKF93bMm9iawA"
      },
      {
        "index_name": ".ds-logs-000002",
        "index_uuid": "Wzxq0VhsQKyPxHhaK3WYAg"
      }
    ],
    "generation": 2
  }
]
----
// TESTRESPONSE[skip:unable to assert responses with top level array]

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

////
[source,console]
----
PUT /_index_template/logs_data_stream
{
  "index_patterns": [ "logs*" ],
  "data_stream": {
    "timestamp_field": "@timestamp"
  },
  "template": {
    "mappings": {
      "properties": {
        "@timestamp": {
          "type": "date"
        }
      }
    }
  }
}

PUT /_index_template/new_logs_data_stream
{
  "index_patterns": [ "new_logs*" ],
  "data_stream": {
    "timestamp_field": "@timestamp"
  },
  "template": {
    "mappings": {
      "properties": {
        "@timestamp": {
          "type": "date"
        }
      }
    }
  }
}

PUT /_data_stream/logs

PUT /_data_stream/new_logs
----
////

[source,console]
----
POST /_reindex
{
  "source": {
    "index": ".ds-logs-000001"
  },
  "dest": {
    "index": "new_logs",
    "op_type": "create"
  }
}
----
// TEST[continued]
====
+
You can also use a query to reindex only a subset of documents with each
request.
+
.*Example*
[%collapsible]
====
The following <<docs-reindex,reindex API>> request copies documents from the
`logs` data stream to the `new_logs` 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": "logs",
    "query": {
      "range": {
        "@timestamp": {
          "gte": "now-7d/d",
          "lte": "now/d"
        }
      }
    }
  },
  "dest": {
    "index": "new_logs",
    "op_type": "create"
  }
}
----
// TEST[continued]
====

. 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.
+
.*Example*
[%collapsible]
====
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
  }
}
----
// TEST[continued]
====

. 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.
+
.*Example*
[%collapsible]
====
The following <<indices-delete-data-stream,delete data stream API>> request
deletes the `logs` data stream. This request also deletes the stream's backing
indices and any data they contain.

[source,console]
----
DELETE /_data_stream/logs
----
// TEST[continued]
====

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

DELETE /_index_template/logs_data_stream

DELETE /_index_template/new_logs_data_stream
----
// TEST[continued]
////
