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WARNING: Version 6.2 of Elasticsearch has passed its EOL date.

This documentation is no longer being maintained and may be removed. If you are running this version, we strongly advise you to upgrade. For the latest information, see the current release documentation.

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Elastic Docs ›Elasticsearch Reference [6.2] ›Indices APIs

Indices Segments

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Indices Segments

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Provide low level segments information that a Lucene index (shard level) is built with. Allows to be used to provide more information on the state of a shard and an index, possibly optimization information, data "wasted" on deletes, and so on.

Endpoints include segments for a specific index:

GET /test/_segments
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For several indices:

GET /test1,test2/_segments
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Or for all indices:

GET /_segments
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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": {
                }
              }
            }
          }
        ]
      }
    }
  }
}
_0
The key of the JSON document is the name of the segment. This name is used to generate file names: all files starting with this segment name in the directory of the shard belong to this segment.
generation
A generation number that is basically incremented when needing to write a new segment. The segment name is derived from this generation number.
num_docs
The number of non-deleted documents that are stored in this segment.
deleted_docs
The number of deleted documents that are stored in this segment. It is perfectly fine if this number is greater than 0, space is going to be reclaimed when this segment gets merged.
size_in_bytes
The amount of disk space that this segment uses, in bytes.
memory_in_bytes
Segments need to store some data into memory in order to be searchable efficiently. This number returns the number of bytes that are used for that purpose. A value of -1 indicates that Elasticsearch was not able to compute this number.
committed
Whether the segment has been sync’ed on disk. Segments that are committed would survive a hard reboot. No need to worry in case of 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
Whether the segment is searchable. A value of false would most likely mean that the segment has been written to disk but no refresh occurred since then to make it searchable.
version
The version of Lucene that has been used to write this segment.
compound
Whether the segment is stored in a compound file. When true, this means that Lucene merged all files from the segment in a single one in order to save file descriptors.
attributes
Contains information about whether high compression was enabled

Verbose mode

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

The format of the additional detail information is labelled as experimental in Lucene and it may change in the future.

GET /test/_segments?verbose=true
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Response:

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

        }
    ...
}
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