Exact KNN queries not cached

Elastic Stack Elasticsearch
1

Hi Folks,

I have a cluster with vectors indexed in a knn index and I'd like to find exact K-nearest neighbors for a given vector using score_script. There are about 500K documents in total.

I'm using the following query to find the id of top 10 nearest neighbors(documents) of the test_vector after filtering documents that match test_key

{
          "size": 10,
          "_source": false,
          "fields": ["id"],
          "query": {
            "script_score": {
              "query": {
                "match": {
                  "key.keyword": {{test_key}}
                }
              },
              "script": {
                "source": "knn_score",
                "lang": "knn",
                "params": {
                  "field": "vector",
                  "query_value": {{test_vector}},
                  "space_type": "innerproduct"
                }
              }
            }
          }
 }

Following are my questions

  1. I observe that request_cache and query_cache is not used at all. I confirmed query_cache and request_cache are enabled. I pulled the index stats before and after I queried and I see no change.
    1.1 Can I expect score_script queries to be cached anywhere?
    1.2 Can I update my search query in anyway to utilize caches and inturn improve search latency?
  2. Updating match query to match "key.keyword" from "key" did not improve the latency. Initially, I used match query on just key field to filter documents matching test_key. I found unexpected document ids in the result. So, I changed the query to match on key.keyword and expected it to reduce the search latency because matching on just key returned a lot more documents compared to key.keyword. I understand that the ideal solution will be to use explicit mapping for the key field to be interpreted as Keyword type and use Term queries for exact match. However, I was expecting this change to improve latency. Am i missing something here?

Thanks for your time in advance. Please let me know if you need more info. from my side.

Thanks