[[cat-segments]]
== cat segments

The `segments` command provides low level information about the segments
in the shards of an index. It provides information similar to the
link:indices-segments.html[_segments] endpoint.

[source,sh]
--------------------------------------------------
% curl 'http://localhost:9200/_cat/segments?v'
index shard prirep ip            segment generation docs.count [...]
test  4     p      192.168.2.105 _0               0          1
test1 2     p      192.168.2.105 _0               0          1
test1 3     p      192.168.2.105 _2               2          1
--------------------------------------------------

[source,sh]
--------------------------------------------------
[...] docs.deleted  size size.memory committed searchable version compound
                 0 2.9kb        7818 false     true       4.10.2  true
                 0 2.9kb        7818 false     true       4.10.2  true
                 0 2.9kb        7818 false     true       4.10.2  true
--------------------------------------------------

The output shows information about index names and shard numbers in the first
two columns.

If you only want to get information about segments in one particular index,
you can add the index name in the URL, for example `/_cat/segments/test`. Also,
several indexes can be queried like `/_cat/segments/test,test1`


The following columns provide additional monitoring information:

prirep::        Whether this segment belongs to a primary or replica shard.

ip::            The ip address of the segments shard.

segment::       A segment name, derived from the segment generation. The name
                is internally used to generate the file names in the directory
                of the shard this segment belongs to.

generation::    The generation number is incremented with each segment that is written.
                The name of the segment is derived from this generation number.

docs.count::    The number of non-deleted documents that are stored in this segment.

docs.deleted::  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::          The amount of disk space that this segment uses.

size.memory::   Segments store some data into memory in order to be searchable efficiently.
                This column shows the number of bytes in memory that are used.

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.

searchable::    True if 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.
