How is total storage per index calculated in OpenSearch?

OpenSearch
,
1

Hi everyone, I trust you all are well!

I’m trying to understand how OpenSearch calculates the total storage used per index. Specifically, I want to clarify whether the following components are considered in the storage cost:

  1. Option 1: Total document size on the cluster is based only on the field size.

  2. Option 2: Total storage includes both _source and field data.

For reference, I’m using the following query:

GET sample_indexing_test/_search

{

“size”: 10,

“stored_fields”: [“_size”],

“query”: {

"match_all": {}

},

“fields”: [“*”],

“_source”: true

}

And here’s a sample response:

{

“_index”: “sample_indexing_test”,

“_id”: “WV91o5gBUI7NisIKDqg5”,

“_score”: 1,

“_size”: 170,

“_source”: {

"title": "OpenSearch for Beginners",

"category": "Books",

"description": "A complete guide to OpenSearch basics.",

"price": 29.99,

"sku": "BK-OS-001"

},

“fields”: {

"price": \[29.99\],

"description": \["A complete guide to OpenSearch basics."\],

"title": \["OpenSearch for Beginners"\],

"sku": \["BK-OS-001"\],

"category": \["Books"\]

}

}

Given this, I’d like to understand whether the _size value reflects just the _source, just the fields, or both. And ultimately, how does this relate to the actual storage footprint of the index?

Any insights or references to documentation would be greatly appreciated.

Thanks in advance!