ElasticSearch _knn_search query on multiple fields - elasticsearch

Question

I'm using ES 8.2. I'd like to use approximate method of _knn_search on more than 1 vector. Below I've attached my current code searching on a single vector. So far as I've read _knn_search does not support search on nested fields.
Alternatively, I can use multi index search. One index, one vector, one search, sum up all results together. However, I need to store all these vectors together in one index as I need also to perform filtration on some other fields besides vectors for knn search.
Thus, the question is if there is a work around how I can perform _knn_search on more than 1 vector?
search_vector = np.zeros(512).tolist()
es_query = {
"knn": {
"field": "feature_vector_1.vector",
"query_vector": search_vector,
"k": 100,
"num_candidates": 1000
},
"filter": [
{
"range": {
"feature_vector_1.match_prc": {
"gt": 10
}
}
}
],
"_source": {
"excludes": ["feature_vector_1.vector", "feature_vector_2.vector"]
}
}

Answer 1

The last working query that I've end up with is
es_query = {
"knn": {
"field": "feature_vector_1.vector",
"query_vector": search_vector,
"k": 1000,
"num_candidates": 1000
},
"filter": [
{
"function_score": {
"query": {
"match_all": {}
},
"script_score": {
"script": {
"source": """
double value = dotProduct(params.queryVector, 'feature_vector_2.vector');
return 100 * (1 + value) / 2;
""",
"params": {
"queryVector": search_vector
}
},
}
}
}
],
"_source": {
"excludes": ["feature_vector_1.vector", "feature_vector_2.vector"]
}
}
However, it is not true AKNN on 2 vectors but still working option if performance of such query satisfies your expectations.

Answer 2

the below seems to be working for me for combining KNN searches, taking the average of multiple cosine similarity scores. Note that this is a little different than the original request, since it performs a brute force search, but you can still filter the results up front by replacing the match_all bit.
GET my-index/_search
{
"query": {
"script_score": {
"query": {
"match_all": {}
},
"script": {
"source": "(cosineSimilarity(params.vector1, 'my-vector1') + cosineSimilarity(params.vector2, 'my-vector2'))/2 + 1.0",
"params": {
"vector1": [
1.3012068271636963,
...
0.23468133807182312
],
"vector2": [
-0.49404603242874146,
...
-0.15835021436214447
]
}
}
}
}
}