# What is in Segments Memory?
**URL:** https://discuss.elastic.co/t/what-is-in-segments-memory/61651
**Category:** Elasticsearch
**Created:** [September 28, 2016, 4:22am UTC](https://discuss.elastic.co/t/what-is-in-segments-memory/61651 "2016-09-28T04:22:29Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@Michael\_Sander](https://discuss.elastic.co/u/Michael_Sander)
#### Post date: [September 28, 2016, 4:22am UTC](https://discuss.elastic.co/t/what-is-in-segments-memory/61651/1 "2016-09-28T04:22:29Z")
###What is in segments memory?
```
GET _stats/?pretty&human
{
"segments" : {
"count" : 160,
"memory" : "24.5gb",
} ...
}
```
I thought segments were stored as files, cached by the OS, and did not reside in ES's heap. However, that does not seem to be the case. The [documentation only says](https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-segments.html) that "[s]egments need to store some data into memory in order to be searchable efficiently." What is this "some data"?
---
### Author:  [@mikemccand](https://discuss.elastic.co/u/mikemccand)
#### Post date: [September 30, 2016, 6:28am UTC](https://discuss.elastic.co/t/what-is-in-segments-memory/61651/2 "2016-09-30T06:28:42Z")
There is an in-memory terms index, stored as an FST, that Lucene uses to quickly determine which on-disk block might contain a requested term.
Dimensional points for numeric range filters (coming in 5.0) also has a small in memory tree structure.
Deleted documents bitset (only if there are deletions).
Doc values and stored fields codec formats also have small in-memory structures.
Recent versions of ES break out more details if you pass `&verbose=true` to the Indices Segments API:
[https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-segments.html](https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-segments.html)
Mike McCandless
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [July 5, 2017, 10:15pm UTC](https://discuss.elastic.co/t/what-is-in-segments-memory/61651/3 "2017-07-05T22:15:54Z")