Index segments API

Returns low-level information about the Lucene segments in index shards. For data streams, the API returns information about the stream’s backing indices.

GET /my-index-000001/_segments

Request

GET /<target>/_segments

GET /_segments

Path parameters

<target>

(Optional, string) Comma-separated list of data streams, indices, and index aliases used to limit the request. Wildcard expressions (*) are supported.

To target all data streams and indices in a cluster, omit this parameter or use _all or *.

Query parameters

allow_no_indices

(Optional, boolean) If true, the request does not return an error if a wildcard expression or _all value retrieves only missing or closed indices.

This parameter also applies to index aliases that point to a missing or closed index.

Defaults to true.

expand_wildcards

(Optional, string) Controls what kind of indices that wildcard expressions can expand to. Multiple values are accepted when separated by a comma, as in open,hidden. Valid values are:

• all

  Expand to open and closed indices, including hidden indices.

  open

  Expand only to open indices.

  closed

  Expand only to closed indices.

  hidden

  Expansion of wildcards will include hidden indices. Must be combined with open, closed, or both.

  none

  Wildcard expressions are not accepted.

Defaults to open.

ignore_unavailable

(Optional, boolean) If true, missing or closed indices are not included in the response. Defaults to false.

verbose

[experimental] This functionality is experimental and may be changed or removed completely in a future release. Elastic will take a best effort approach to fix any issues, but experimental features are not subject to the support SLA of official GA features. (Optional, boolean) If true, the response includes detailed information about Lucene’s memory usage. Defaults to false.

Response body

<segment>

(String) Name of the segment, such as _0. The segment name is derived from the segment generation and used internally to create file names in the directory of the shard.

generation

(Integer) Generation number, such as 0. Elasticsearch increments this generation number for each segment written. Elasticsearch then uses this number to derive the segment name. Generation number, such as 0. Elasticsearch increments this generation number for each segment written. Elasticsearch then uses this number to derive the segment name.

num_docs

(Integer) The number of documents as reported by Lucene. This excludes deleted documents and counts any nested documents separately from their parents. It also excludes documents which were indexed recently and do not yet belong to a segment.

deleted_docs

(Integer) The number of deleted documents as reported by Lucene, which may be higher or lower than the number of delete operations you have performed. This number excludes deletes that were performed recently and do not yet belong to a segment. Deleted documents are cleaned up by the automatic merge process if it makes sense to do so. Also, Elasticsearch creates extra deleted documents to internally track the recent history of operations on a shard.

size_in_bytes

(Integer) Disk space used by the segment, such as 50kb.

memory_in_bytes

(Integer) Bytes of segment data stored in memory for efficient search, such as 1264.

A value of -1 indicates Elasticsearch was unable to compute this number.

committed

(Boolean) If true, the segments is synced to disk. Segments that are synced can survive a hard reboot.

If false, the data from uncommitted segments is also stored in the transaction log so that Elasticsearch is able to replay changes on the next start.

search

(Boolean) If true, the segment is searchable.

If false, the segment has most likely been written to disk but needs a refresh to be searchable.

version

(String) Version of Lucene used to write the segment.

compound

(Boolean) If true, Lucene merged all files from the segment into a single file to save file descriptors.

attributes

(Object) Contains information about whether high compression was enabled.

Examples

Get segment information for a specific data stream or index

GET /test/_segments

Get segment information for several data streams and indices

GET /test1,test2/_segments

Get segment information for all data streams and indices in a cluster

GET /_segments

The API returns the following response:

{
  "_shards": ...
  "indices": {
    "test": {
      "shards": {
        "0": [
          {
            "routing": {
              "state": "STARTED",
              "primary": true,
              "node": "zDC_RorJQCao9xf9pg3Fvw"
            },
            "num_committed_segments": 0,
            "num_search_segments": 1,
            "segments": {
              "_0": {
                "generation": 0,
                "num_docs": 1,
                "deleted_docs": 0,
                "size_in_bytes": 3800,
                "memory_in_bytes": 1410,
                "committed": false,
                "search": true,
                "version": "7.0.0",
                "compound": true,
                "attributes": {
                }
              }
            }
          }
        ]
      }
    }
  }
}

Verbose mode

To add additional information that can be used for debugging, use the verbose flag.

This functionality is experimental and may be changed or removed completely in a future release. Elastic will take a best effort approach to fix any issues, but experimental features are not subject to the support SLA of official GA features.

GET /test/_segments?verbose=true

The API returns the following response:

{
  ...
    "_0": {
      ...
      "ram_tree": [
        {
          "description": "postings [PerFieldPostings(format=1)]",
          "size_in_bytes": 2696,
          "children": [
            {
              "description": "format 'Lucene50_0' ...",
              "size_in_bytes": 2608,
              "children" :[ ... ]
            },
            ...
          ]
        },
        ...
      ]
    }
  ...
}