# Using painless scripting to re-implement BM25 scoring
**URL:** https://discuss.elastic.co/t/using-painless-scripting-to-re-implement-bm25-scoring/195802
**Category:** Elasticsearch
**Tags:** painless
**Created:** [August 19, 2019, 7:06pm UTC](https://discuss.elastic.co/t/using-painless-scripting-to-re-implement-bm25-scoring/195802 "2019-08-19T19:06:45Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@dpappas](https://discuss.elastic.co/u/dpappas)
#### Post date: [August 19, 2019, 7:06pm UTC](https://discuss.elastic.co/t/using-painless-scripting-to-re-implement-bm25-scoring/195802/1 "2019-08-19T19:06:45Z")
Hello everyone
I have indexed a few hundreds of millions of data into ElasticSearch using the default parameters of b and k1. It is prohibitive for me to reindex the data however i would like to optimize the parameters b and k1 of bm25 for better scoring.
To my understanding there are some functions in Painless scripting that could compute/fetch tf and idf scores of a token in a document.
Could you please reproduce BM25 in Painless scripting so that i could tune the b and k1 parameters?
Thank you all in advance
Dimitris
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### Author:  [@rjernst](https://discuss.elastic.co/u/rjernst)
#### Post date: [August 19, 2019, 10:10pm UTC](https://discuss.elastic.co/t/using-painless-scripting-to-re-implement-bm25-scoring/195802/2 "2019-08-19T22:10:15Z")
In Elasticsearch the module implementing textual scoring is called similarity. There isn't a need to write a painless script, since b and k1 can be [customized](https://www.elastic.co/guide/en/elasticsearch/reference/current/index-modules-similarity.html#index-modules-similarity). However if you are intent on using painless, you can write a [similarity script](https://www.elastic.co/guide/en/elasticsearch/reference/current/index-modules-similarity.html#scripted_similarity).
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### Author:  [@dpappas](https://discuss.elastic.co/u/dpappas)
#### Post date: [August 19, 2019, 10:28pm UTC](https://discuss.elastic.co/t/using-painless-scripting-to-re-implement-bm25-scoring/195802/3 "2019-08-19T22:28:55Z")
Unfortunately this will not work.
As i mentioned i do not want to reindex.
I have hundreds of millions of data.
i just need to optimize the values of b and k1.
I just want to replicate bm25 with painless scripting so to just change thw values of b and k1 as needed.
Thank you again
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### Author:  [@rjernst](https://discuss.elastic.co/u/rjernst)
#### Post date: [August 19, 2019, 11:27pm UTC](https://discuss.elastic.co/t/using-painless-scripting-to-re-implement-bm25-scoring/195802/4 "2019-08-19T23:27:16Z")
The similarity can be changed on an existing index, no reindexing necessary. What do you see implying reindexing would be needed?
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### Author:  [@dpappas](https://discuss.elastic.co/u/dpappas)
#### Post date: [August 20, 2019, 9:44am UTC](https://discuss.elastic.co/t/using-painless-scripting-to-re-implement-bm25-scoring/195802/5 "2019-08-20T09:44:50Z")
I thought that "PUT /index ..." is a creation of an index.
Dont i need to re-index the data once i change the mapping/settings ?
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### Author:  [@rjernst](https://discuss.elastic.co/u/rjernst)
#### Post date: [August 21, 2019, 12:16am UTC](https://discuss.elastic.co/t/using-painless-scripting-to-re-implement-bm25-scoring/195802/6 "2019-08-21T00:16:33Z")
While some settings cannot be changed (eg `number_of_shards`) many settings can be, like the configured similarity. Use the [update settings api](https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-update-settings.html).
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### Author:  [@rjernst](https://discuss.elastic.co/u/rjernst)
#### Post date: [August 21, 2019, 12:17am UTC](https://discuss.elastic.co/t/using-painless-scripting-to-re-implement-bm25-scoring/195802/7 "2019-08-21T00:17:45Z")
> Dont i need to re-index the data once i change the mapping/settings ?
Since the similarity settings are not baked into the index, changing these parameters does not requiring reindexing.
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### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [September 18, 2019, 12:17am UTC](https://discuss.elastic.co/t/using-painless-scripting-to-re-implement-bm25-scoring/195802/8 "2019-09-18T00:17:49Z")
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