INVERTED

When you need to perform frequent filter queries on your data, INVERTED indexes can dramatically improve query performance. Instead of scanning through all documents, Zilliz Cloud uses inverted indexes to quickly locate the exact records that match your filter conditions.

When to use INVERTED indexes

Use INVERTED indexes when you need to:

• Filter by specific values: Find all records where a field equals a specific value (e.g., category == "electronics")

• Filter text content: Perform efficient searches on VARCHAR fields

• Query JSON field values: Filter on specific keys within JSON structures

Performance benefit: INVERTED indexes can reduce query time from seconds to milliseconds on large datasets by eliminating the need for full collection scans.

How INVERTED indexes work

An INVERTED index in Zilliz Cloud maps each unique field value (term) to the set of document IDs where that value occurs. This structure enables fast lookups for fields with repeated or categorical values.

As shown in the diagram, the process works in two steps:

1. Forward mapping (ID → Term): Each document ID points to the field value it contains.

2. Inverted mapping (Term → IDs): Zilliz Cloud collects unique terms and builds a reverse mapping from each term to all IDs that contain it.

For example, the value "electronics" maps to IDs 1 and 3, while "books" maps to IDs 2 and 5.

When you filter for a specific value (e.g., category == "electronics"), Zilliz Cloud simply looks up the term in the index and retrieves the matching IDs directly. This avoids scanning the full dataset and enables fast filtering, especially for categorical or repeated values.

INVERTED indexes support all scalar field types, such as BOOL, INT8, INT16, INT32, INT64, FLOAT, DOUBLE, VARCHAR, JSON, and ARRAY. However, the index parameters for indexing a JSON field are slightly different from regular scalar fields.

Create indexes on non-JSON fields

To create an index on a non-JSON field, follow these steps:

1. Prepare your index parameters:

   Python

   python

   from pymilvus import MilvusClient
   
   client = MilvusClient(uri="YOUR_CLUSTER_ENDPOINT") # Replace with your server address
   
   # Create an empty index parameter object
   index_params = client.prepare_index_params()

   Java

   java

   import io.milvus.v2.client.ConnectConfig;
   import io.milvus.v2.client.MilvusClientV2;
   
   // Initialize Milvus client
   MilvusClientV2 client = new MilvusClientV2(ConnectConfig.builder()
           .uri("YOUR_CLUSTER_ENDPOINT") // Replace with your server address
           .build());

   Go

   go

   import (
       "context"
       "fmt"
   
       "github.com/milvus-io/milvus/client/v3/milvusclient"
   )
   
   ctx, cancel := context.WithCancel(context.Background())
   defer cancel()
   
   // Initialize Milvus client
   client, err := milvusclient.New(ctx, &milvusclient.ClientConfig{
       Address: "YOUR_CLUSTER_ENDPOINT", // Replace with your server address
   })
   if err != nil {
       fmt.Println(err.Error())
       // handle error
   }

   Rust

   rust

   use milvus::v2::prelude::*;
   
   // Initialize Milvus client
   let config = ConnectConfig::new().uri("YOUR_CLUSTER_ENDPOINT"); // Replace with your server address
   let client = ClientV2::new(&config).await?;

   C++

   c++

   #include "milvus/MilvusClientV2.h"
   
   // Initialize Milvus client
   auto client = milvus::MilvusClientV2::Create();
   auto status = client->Connect(milvus::ConnectParam("YOUR_CLUSTER_ENDPOINT")); // Replace with your server address
   if (!status.IsOk()) {
       std::cout << status.Message() << std::endl;
   }

   NodeJS

   javascript

   import { MilvusClient } from "@zilliz/milvus2-sdk-node";
   
   // Initialize Milvus client
   const client = new MilvusClient({
       address: "YOUR_CLUSTER_ENDPOINT", // Replace with your server address
   });

   cURL

   bash

   export CLUSTER_ENDPOINT="YOUR_CLUSTER_ENDPOINT" # Replace with your server address
   export TOKEN="YOUR_CLUSTER_TOKEN"

2. Add the INVERTED index:

   Python

   python

   index_params.add_index(
       field_name="category",           # Name of the field to index
       index_type="INVERTED",          # Specify INVERTED index type
       index_name="category_index"     # Give your index a name
   )

   Java

   java

   import io.milvus.v2.common.IndexParam;
   
   // Add the INVERTED index
   IndexParam indexParam = IndexParam.builder()
           .fieldName("category") // Name of the field to index
           .indexType(IndexParam.IndexType.INVERTED) // Specify INVERTED index type
           .indexName("category_index") // Give your index a name
           .build();

   Go

   go

   import "github.com/milvus-io/milvus/client/v3/index"
   
   // Add the INVERTED index
   idx := index.NewInvertedIndex() // Specify INVERTED index type
   idx.WithIndexName("category_index") // Give your index a name

   Rust

   rust

   // Add the INVERTED index
   let index_params = vec![
       IndexParam::new()
           .field_name("category") // Name of the field to index
           .index_type(IndexType::Inverted) // Specify INVERTED index type
           .index_name("category_index"), // Give your index a name
   ];

   C++

   c++

   // Add the INVERTED index
   milvus::IndexDesc index_desc("category", "category_index", milvus::IndexType::INVERTED); // field name, index name, index type

   NodeJS

   javascript

   import { IndexType } from "@zilliz/milvus2-sdk-node";
   
   // Add the INVERTED index
   const indexParams = {
       field_name: "category", // Name of the field to index
       index_type: IndexType.INVERTED, // Specify INVERTED index type
       index_name: "category_index", // Give your index a name
   };

   cURL

   bash

   # Add the INVERTED index
   export indexParams='[
       {
           "fieldName": "category", # Name of the field to index
           "indexName": "category_index", # Give your index a name
           "params": {
               "index_type": "INVERTED" # Specify INVERTED index type
           }
       }
   ]'

3. Create the index:

   Python

   python

   client.create_index(
       collection_name="my_collection", # Replace with your collection name
       index_params=index_params
   )

   Java

   java

   import io.milvus.v2.service.index.request.CreateIndexReq;
   import java.util.Collections;
   
   // Create the index
   client.createIndex(CreateIndexReq.builder()
           .collectionName("my_collection") // Replace with your collection name
           .indexParams(Collections.singletonList(indexParam))
           .build());

   Go

   go

   import "github.com/milvus-io/milvus/client/v3/milvusclient"
   
   // Create the index
   _, err = client.CreateIndex(ctx, milvusclient.NewCreateIndexOption("my_collection", "category", idx)) // Replace with your collection name
   if err != nil {
       fmt.Println(err.Error())
       // handle error
   }

   Rust

   rust

   // Create the index
   client
       .create_index(
           CreateIndexRequest::builder()
               .collection_name("my_collection") // Replace with your collection name
               .index_params(index_params)
               .build()?,
       )
       .await?;

   C++

   c++

   // Create the index
   status = client->CreateIndex(milvus::CreateIndexRequest()
                                    .WithCollectionName("my_collection") // Replace with your collection name
                                    .WithIndexes({std::move(index_desc)}));
   if (!status.IsOk()) {
       std::cout << status.Message() << std::endl;
   }

   NodeJS

   javascript

   // Create the index
   await client.createIndex({
       collection_name: "my_collection", // Replace with your collection name
       field_name: indexParams.field_name,
       index_type: indexParams.index_type,
       index_name: indexParams.index_name,
   });

   cURL

   bash

   # Create the index
   curl --request POST \
   --url "${CLUSTER_ENDPOINT}/v2/vectordb/indexes/create" \
   --header "Authorization: Bearer ${TOKEN}" \
   --header "Content-Type: application/json" \
   -d "{
       \"collectionName\": \"my_collection\", # Replace with your collection name
       \"indexParams\": $indexParams
   }"

Create indexes on JSON fields

You can also create INVERTED indexes on specific paths within JSON fields. This requires additional parameters to specify the JSON path and data type:

Python

python

# Build index params
index_params.add_index(
    field_name="metadata",                    # JSON field name
    index_type="INVERTED",
    index_name="metadata_category_index",
    params={
        "json_path": "metadata[\"category\"]",    # Path to the JSON key
        "json_cast_type": "varchar"              # Data type to cast to during indexing
    }
)

# Create index
client.create_index(
    collection_name="my_collection", # Replace with your collection name
    index_params=index_params
)

Java

java

import io.milvus.v2.common.IndexParam;
import io.milvus.v2.service.index.request.CreateIndexReq;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

// Build index params
Map<String, Object> extraParams = new HashMap<>();
extraParams.put("json_path", "metadata[\"category\"]"); // Path to the JSON key
extraParams.put("json_cast_type", "varchar"); // Data type to cast to during indexing

IndexParam jsonIndexParam = IndexParam.builder()
        .fieldName("metadata") // JSON field name
        .indexType(IndexParam.IndexType.INVERTED)
        .indexName("metadata_category_index")
        .extraParams(extraParams)
        .build();

// Create index
client.createIndex(CreateIndexReq.builder()
        .collectionName("my_collection") // Replace with your collection name
        .indexParams(Collections.singletonList(jsonIndexParam))
        .build());

Go

go

import (
    "github.com/milvus-io/milvus/client/v3/index"
    "github.com/milvus-io/milvus/client/v3/milvusclient"
)

// Build index params
jsonIdx := index.NewJSONPathIndex(index.Inverted, "varchar", "metadata[\"category\"]") // indexType, json_cast_type, json_path
jsonIdx.WithIndexName("metadata_category_index")

// Create index
_, err = client.CreateIndex(ctx, milvusclient.NewCreateIndexOption("my_collection", "metadata", jsonIdx)) // Replace with your collection name
if err != nil {
    fmt.Println(err.Error())
    // handle error
}

Rust

rust

use std::collections::HashMap;

// Build index params
let json_index_params = vec![
    IndexParam::new()
        .field_name("metadata") // JSON field name
        .index_type(IndexType::Inverted)
        .index_name("metadata_category_index")
        .extra_params(HashMap::from([
            ("json_path".into(), "metadata[\"category\"]".into()), // Path to the JSON key
            ("json_cast_type".into(), "varchar".into()), // Data type to cast to during indexing
        ])),
];

// Create index
client
    .create_index(
        CreateIndexRequest::builder()
            .collection_name("my_collection") // Replace with your collection name
            .index_params(json_index_params)
            .build()?,
    )
    .await?;

C++

c++

// Build index params
milvus::IndexDesc json_index_desc("metadata", "metadata_category_index", milvus::IndexType::INVERTED); // JSON field name, index name, index type
json_index_desc.AddExtraParam("json_path", "metadata[\"category\"]"); // Path to the JSON key
json_index_desc.AddExtraParam("json_cast_type", "varchar"); // Data type to cast to during indexing

// Create index
status = client->CreateIndex(milvus::CreateIndexRequest()
                                 .WithCollectionName("my_collection") // Replace with your collection name
                                 .WithIndexes({std::move(json_index_desc)}));
if (!status.IsOk()) {
    std::cout << status.Message() << std::endl;
}

NodeJS

javascript

import { IndexType } from "@zilliz/milvus2-sdk-node";

// Build index params
await client.createIndex({
    collection_name: "my_collection", // Replace with your collection name
    field_name: "metadata", // JSON field name
    index_type: IndexType.INVERTED,
    index_name: "metadata_category_index",
    params: {
        json_path: "metadata[\"category\"]", // Path to the JSON key
        json_cast_type: "varchar", // Data type to cast to during indexing
    },
});

cURL

bash

# Build index params
curl --request POST \
--url "${CLUSTER_ENDPOINT}/v2/vectordb/indexes/create" \
--header "Authorization: Bearer ${TOKEN}" \
--header "Content-Type: application/json" \
-d '{
    "collectionName": "my_collection", # Replace with your collection name
    "indexParams": [
        {
            "fieldName": "metadata", # JSON field name
            "indexName": "metadata_category_index",
            "params": {
                "index_type": "INVERTED",
                "json_path": "metadata[\"category\"]", # Path to the JSON key
                "json_cast_type": "varchar" # Data type to cast to during indexing
            }
        }
    ]
}'

For detailed information about JSON field indexing, including supported paths, data types, and limitations, refer to JSON Indexing.

Drop an index

Use the drop_index() method to remove an existing index from a collection.

Notes

In your cluster compatible with Milvus v2.6.x, you can drop a scalar index directly once it’s no longer needed—no need to release the collection first.

Python

python

client.drop_index(
    collection_name="my_collection",   # Name of the collection
    index_name="category_index" # Name of the index to drop
)

Java

java

import io.milvus.v2.client.ConnectConfig;
import io.milvus.v2.client.MilvusClientV2;
import io.milvus.v2.service.index.request.DropIndexReq;

MilvusClientV2 client = new MilvusClientV2(ConnectConfig.builder()
        .uri("YOUR_CLUSTER_ENDPOINT")
        .token("YOUR_CLUSTER_TOKEN")
        .build());

client.dropIndex(DropIndexReq.builder()
        .collectionName("my_collection")
        .indexName("category_index")
        .build());

Go

go

import "github.com/milvus-io/milvus/client/v3/milvusclient"

err := client.DropIndex(ctx, milvusclient.NewDropIndexOption("my_collection", "category_index"))
if err != nil {
    log.Fatal(err)
}

Rust

rust

use milvus::v2::prelude::*;

let client = ClientV2::new(&ConnectConfig::new().uri("YOUR_CLUSTER_ENDPOINT").token("YOUR_CLUSTER_TOKEN")).await?;

client
    .drop_index(
        DropIndexRequest::builder()
            .collection_name("my_collection")
            .index_name("category_index")
            .build()?,
    )
    .await?;

C++

c++

#include <iostream>
#include "milvus/MilvusClientV2.h"

auto client = milvus::MilvusClientV2::Create();

milvus::ConnectParam connect_param{"YOUR_CLUSTER_ENDPOINT", "YOUR_CLUSTER_TOKEN"};
auto status = client->Connect(connect_param);
if (!status.IsOk()) {
    std::cout << status.Message() << std::endl;
}

status = client->DropIndex(milvus::DropIndexRequest()
                           .WithCollectionName("my_collection")
                           .WithIndexName("category_index"));
if (!status.IsOk()) {
    std::cout << status.Message() << std::endl;
}

NodeJS

javascript

import { MilvusClient } from "@zilliz/milvus2-sdk-node";

const client = new MilvusClient({
    address: "YOUR_CLUSTER_ENDPOINT",
    token: "YOUR_CLUSTER_TOKEN"
});

await client.dropIndex({
    collection_name: "my_collection",
    index_name: "category_index"
});

cURL

bash

export CLUSTER_ENDPOINT="YOUR_CLUSTER_ENDPOINT"
export TOKEN="YOUR_CLUSTER_TOKEN"

curl --request POST \
--url "${CLUSTER_ENDPOINT}/v2/vectordb/indexes/drop" \
--header "Authorization: Bearer ${TOKEN}" \
--header "Content-Type: application/json" \
-d '{
    "collectionName": "my_collection",
    "indexName": "category_index"
}'

Best practices

• Create indexes after loading data: Build indexes on collections that already contain data for better performance

• Use descriptive index names: Choose names that clearly indicate the field and purpose

• Monitor index performance: Check query performance before and after creating indexes

• Consider your query patterns: Create indexes on fields you frequently filter by

Next steps

• Learn about AUTOINDEX.

• See JSON Indexing for advanced JSON indexing scenarios