﻿---
title: Index sorting settings
description: When creating a new index in Elasticsearch it is possible to configure how the segments inside each shard will be sorted. By default Lucene does not apply...
url: https://www.elastic.co/elastic/docs-builder/docs/2826/reference/elasticsearch/index-settings/sorting
products:
  - Elasticsearch
applies_to:
  - Elastic Cloud Serverless: Generally available
  - Elastic Stack: Generally available
---

# Index sorting settings
When creating a new index in Elasticsearch it is possible to configure how the segments inside each shard will be sorted. By default Lucene does not apply any sort. The `index.sort.*` settings define which fields should be used to sort the documents inside each Segment.
<warning>
  It is allowed to apply index sorting to mappings with nested objects, so long as the `index.sort.*` setting contains no nested fields.
</warning>

For instance the following example shows how to define a sort on a single field:
```json

{
  "settings": {
    "index": {
      "sort.field": "date", <1>
      "sort.order": "desc"  <2>
    }
  },
  "mappings": {
    "properties": {
      "date": {
        "type": "date"
      }
    }
  }
}
```

It is also possible to sort the index by more than one field:
```json

{
  "settings": {
    "index": {
      "sort.field": [ "username", "date" ], <1>
      "sort.order": [ "asc", "desc" ]       <2>
    }
  },
  "mappings": {
    "properties": {
      "username": {
        "type": "keyword",
        "doc_values": true
      },
      "date": {
        "type": "date"
      }
    }
  }
}
```

Index sorting supports the following settings:
<definitions>
  <definition term="">
    The list of fields used to sort the index. Only `boolean`, `numeric`, `date` and `keyword` fields with `doc_values` are allowed here.
  </definition>
  <definition term="">
    The sort order to use for each field. The order option can have the following values:
    - `asc`:  For ascending order.
    - `desc`: For descending order.
    When `index.sort.field` is set but `index.sort.order` is not explicitly provided, each field defaults to `asc`.
  </definition>
  <definition term="">
    Elasticsearch supports sorting by multi-valued fields. The mode option controls what value is picked to sort the document. The mode option can have the following values:
    - `min`: 	Pick the lowest value.
    - `max`: 	Pick the highest value.
    When `index.sort.order` is set to `asc`, `index.sort.mode` defaults to `min`. If you set the order to `desc`, the mode defaults to `max`.
  </definition>
  <definition term="">
    The missing parameter specifies how docs which are missing the field should be treated. The missing value can have the following values:
    - `_last`: Documents without value for the field are sorted last.
    - `_first`: Documents without value for the field are sorted first.
    Documents missing the sort field are always sorted last by default, regardless of sort order.
  </definition>
</definitions>

<warning>
  Index sorting can be defined only once at index creation. It is not allowed to add or update a sort on an existing index. Index sorting also has a cost in terms of indexing throughput since documents must be sorted at flush and merge time. You should test the impact on your application before activating this feature.
</warning>


## Early termination of search request

By default in Elasticsearch a search request must visit every document that matches a query to retrieve the top documents sorted by a specified sort. Though when the index sort and the search sort are the same it is possible to limit the number of documents that should be visited per segment to retrieve the N top ranked documents globally. For example, let’s say we have an index that contains events sorted by a timestamp field:
```json

{
  "settings": {
    "index": {
      "sort.field": "timestamp",
      "sort.order": "desc" <1>
    }
  },
  "mappings": {
    "properties": {
      "timestamp": {
        "type": "date"
      }
    }
  }
}
```

You can search for the last 10 events with:
```json

{
  "size": 10,
  "sort": [
    { "timestamp": "desc" }
  ]
}
```

Elasticsearch will detect that the top docs of each segment are already sorted in the index and will only compare the first N documents per segment. The rest of the documents matching the query are collected to count the total number of results and to build aggregations.
If you’re only looking for the last 10 events and have no interest in the total number of documents that match the query you can set `track_total_hits` to false:
```json

{
  "size": 10,
  "sort": [ <1>
      { "timestamp": "desc" }
  ],
  "track_total_hits": false
}
```

This time, Elasticsearch will not try to count the number of documents and will be able to terminate the query as soon as N documents have been collected per segment.
```json
{
  "_shards": ...
   "hits" : {  
      "max_score" : null,
      "hits" : []
  },
  "took": 20,
  "timed_out": false
}
```

<note>
  Aggregations will collect all documents that match the query regardless of the value of `track_total_hits`
</note>