Where should I adjust the k1 and b parameters of BM25?

[PKQ1688]

When using BM25Retriever, how can I adjust the values of K1 and b?

[masci]

That ultimately depends on the Document Store you are using. For ElasticsearchDocumentStore and OpensearchDocumentStore you can pass a field called custom_mapping to the constructor that will be used to create the documents index. There you can pass the BM25 parameters you want. Do not forget to also pass the default mappings and configs required by Haystack, you can see what they are here:

haystack/haystack/document_stores/elasticsearch.py

Line 423 in 7db025a

mapping = {