# Update similarity measure for existing index
**URL:** https://discuss.elastic.co/t/update-similarity-measure-for-existing-index/20163
**Category:** Elasticsearch
**Created:** [October 9, 2014, 1:58pm UTC](https://discuss.elastic.co/t/update-similarity-measure-for-existing-index/20163 "2014-10-09T13:58:47Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@CC1](https://discuss.elastic.co/u/CC1)
#### Post date: [October 9, 2014, 1:58pm UTC](https://discuss.elastic.co/t/update-similarity-measure-for-existing-index/20163/1 "2014-10-09T13:58:47Z")
I have an existing index for which the default ElasticSearch similarity is
used for all fields. I would like to update this index and set some other
type of similarity, like BM25. The query I tried is:
curl -XPOST '[http://localhost:9200/myindex/](http://localhost:9200/myindex/)' -d '{"settings":{"similarity":{"newSimilarity":{"type":"BM25"}}}}'
However, this crashes with an IndexAlreadyExists exception. Still, is it
possible to update the similarity measure for all fields inside this index
without having to reindex the data?
Thanks!
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### Author:  [@Ivan](https://discuss.elastic.co/u/Ivan)
#### Post date: [October 9, 2014, 5:44pm UTC](https://discuss.elastic.co/t/update-similarity-measure-for-existing-index/20163/2 "2014-10-09T17:44:38Z")
You cannot change the similarity on an existing index. There is no
technical measure why it could not occur, it appears to be simply a method
in place to prevent users from creating potentially huge errors. I say that
developers should have the option to shoot themselves in the foot!
Cheers,
Ivan
On Thu, Oct 9, 2014 at 6:58 AM, CC [cr1st1na.garbacea@gmail.com](mailto:cr1st1na.garbacea@gmail.com) wrote:
> I have an existing index for which the default Elasticsearch similarity is
> used for all fields. I would like to update this index and set some other
> type of similarity, like BM25. The query I tried is:
>
> curl -XPOST '[http://localhost:9200/myindex/](http://localhost:9200/myindex/)' -d '{"settings":{"similarity":{"newSimilarity":{"type":"BM25"}}}}'
>
> However, this crashes with an IndexAlreadyExists exception. Still, is it
> possible to update the similarity measure for all fields inside this index
> without having to reindex the data?
>
> Thanks!
>
> --
> You received this message because you are subscribed to the Google Groups
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> To view this discussion on the web visit
> [https://groups.google.com/d/msgid/elasticsearch/d6463b4f-129b-41de-8fbc-bbc446887b54%40googlegroups.com](https://groups.google.com/d/msgid/elasticsearch/d6463b4f-129b-41de-8fbc-bbc446887b54%40googlegroups.com)
> [https://groups.google.com/d/msgid/elasticsearch/d6463b4f-129b-41de-8fbc-bbc446887b54%40googlegroups.com?utm\_medium=email&utm\_source=footer](https://groups.google.com/d/msgid/elasticsearch/d6463b4f-129b-41de-8fbc-bbc446887b54%40googlegroups.com?utm_medium=email&utm_source=footer)
> .
> For more options, visit [https://groups.google.com/d/optout](https://groups.google.com/d/optout).
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### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [July 6, 2017, 12:57am UTC](https://discuss.elastic.co/t/update-similarity-measure-for-existing-index/20163/3 "2017-07-06T00:57:14Z")