# Similarity Measure Change

**URL:** <https://discuss.elastic.co/t/similarity-measure-change/153358>\
**Category:** Elasticsearch\
**Created:** [October 22, 2018, 9:23am UTC](https://discuss.elastic.co/t/similarity-measure-change/153358 "2018-10-22T09:23:47Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Digant\_Tyagi](https://avatars.discourse-cdn.com/v4/letter/d/b4bc9f/32.png) [@Digant\_Tyagi](https://discuss.elastic.co/u/Digant_Tyagi)\
**Post date:** [October 22, 2018, 9:23am UTC](https://discuss.elastic.co/t/similarity-measure-change/153358/1 "2018-10-22T09:23:47Z")

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Does changing the similarity measure from Classic (based on TF/IDF) in Elastic 2.x to OKapi BM25 in Elastic 6.4 has any impact on overall Elastic search performance?

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**Author:** ![Mark\_Harwood](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/mark_harwood/32/10538_2.png) [@Mark\_Harwood](https://discuss.elastic.co/u/Mark_Harwood)\
**Post date:** [October 22, 2018, 9:35am UTC](https://discuss.elastic.co/t/similarity-measure-change/153358/2 "2018-10-22T09:35:47Z")

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Doesn't look like it. Benchmarks here for a variety of queries:  
[https://home.apache.org/~mikemccand/lucenebench/](https://home.apache.org/~mikemccand/lucenebench/)

Shift drag to scroll graphs to the left and look for the "BI" change in the timeline

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**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [November 19, 2018, 9:35am UTC](https://discuss.elastic.co/t/similarity-measure-change/153358/3 "2018-11-19T09:35:49Z")

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Closed on November 19, 2018, 9:35am UTC

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