# Using multiple similarity metrics on an existing index
**URL:** https://discuss.elastic.co/t/using-multiple-similarity-metrics-on-an-existing-index/296274
**Category:** Elasticsearch
**Created:** [February 4, 2022, 10:03am UTC](https://discuss.elastic.co/t/using-multiple-similarity-metrics-on-an-existing-index/296274 "2022-02-04T10:03:54Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@mkaze](https://discuss.elastic.co/u/mkaze)
#### Post date: [February 4, 2022, 10:03am UTC](https://discuss.elastic.co/t/using-multiple-similarity-metrics-on-an-existing-index/296274/1 "2022-02-04T10:03:55Z")
I was wondering if it's possible to use multiple similarity metrics for an index in Elasticsearch. Let's assume I have already defined an index with a customized BM25 similarity metric (say, with `b=1`), and now I would like to **add another** similarity metric (say, BM25 with `b=0`) to this index. Is this possible? If so, does this imply a re-index? Unfortunately I couldn't find any examples in documentation or elsewhere which uses multiple similarity metrics for the same index; so I was in doubt if this is possible at all?!
Example scenario:
```auto
"index": {
"similarity": {
"BM25_v1": {
"type": "BM25",
"b": 1.0
},
# add a new metric on this index.
"BM25_v2": {
"type": "BM25",
"b": 0.0
}
}
}
```
And its usage:
```auto
{
'some_field': {
'type': 'text',
'norms': 'true',
'similarity': 'BM25_v1' # old metric
},
'another_field': {
'type': 'text',
'norms': 'true',
'similarity': 'BM25_v2' # new metric
},
}
```
---
### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [March 4, 2022, 10:04am UTC](https://discuss.elastic.co/t/using-multiple-similarity-metrics-on-an-existing-index/296274/2 "2022-03-04T10:04:55Z")
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