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Vector Search (Single-Vector and Multi-Vector)

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Terakhir diperbarui: 2026-08-12 18:13:52
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This document introduces the key points of k-nearest neighbor (kNN) search. For more details, refer to the related document.

Single-Vector Search

This is the most basic vector search method, which performs a similarity search on a single vector field.
GET /book-index/_search
{
   "knn": {
      "field": "title_vector",
      "query_vector": [0.1, 0.2, 0.3 ...],
      "k": 10,  // Number of top k results to return
      "num_candidates": 100  // Number of candidate vectors to search on each shard
  }
  "fields": ["id", "title_text", "category"],
  "_source": false,
}

Parameter description:
field: name of the vector field to search
query_vector: query vector. Its dimension must match the field definition.
k: number of the most similar documents to return
num_candidates: number of candidate vectors considered on each shard. A larger value improves accuracy but reduces performance.
You can also directly input the query text to generate the query vector through online inference (same below):
GET /book-index/_search
{
  "knn": {
    "field": "title_vector",
    "query_vector_builder": {
      "text_embedding": {
          "model_id": "model-bge-base",
          "model_text": "Sapiens: A Brief History of Humankind"
      }
    },
    "k": 10,  // Number of top k results to return
    "num_candidates": 100  // Number of candidate vectors to search on each shard
  },
  "fields": ["id", "title_text", "category"],
  "_source": false
}


Multi-Vector Search

ES supports searching multiple vector fields simultaneously and merging the results.
GET /book-index/_search
{
  "query": {
    "bool": {
      "should": [
        {
          "knn": {
            "field": "title_vector",
            "query_vector": [0.1, 0.2, 0.3 ...], 
            "k": 5,
            "num_candidates": 50,
            "boost": 0.8
          }
        },
        {
          "knn": {
            "field": "content_vector", 
            "query_vector": [0.1, 0.2, 0.3, ...], 
            "k": 5,
            "num_candidates": 50,
            "boost": 0.2
          }
        }
      ]
    }
  }
}
Features:
Two search methods are executed in parallel.
The results are merged and sorted by score.
You can use the boost parameter to adjust the weight of each field.
When the same document appears in different search results, the highest score is used.
Topik sebelumnya: Data WritingTopik selanjutnya: Hybrid Search (Pre-Filtering/Post-Filtering/Parallel Search)

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