Elasticsearch  Efficiently Counting Items in an Elasticsearch Index

By Opster Team

Updated: Jul 6, 2023

| 3 min read

Introduction

Counting items in an Elasticsearch index is a common operation that can be performed using various methods. In this article, we will discuss different approaches to count items in an index, their advantages, and limitations. We will also provide examples to help you understand how to use these methods effectively. If you want to learn about Elasticsearch – many index get requests with missing documents, check out this guide.

Using the Count API

The Count API is a simple and efficient way to count the number of documents in an index or a subset of documents that match a specific query. The Count API returns the count of documents without returning the actual documents, making it faster and more resource-efficient than using a search query with a size of 0.

Here’s an example of using the Count API to count all documents in an index named `my_index`:

GET /my_index/_count

To count documents that match a specific query, you can include the query in the request body:

GET /my_index/_count
{
  "query": {
    "match": {
      "field_name": "value"
    }
  }
}

Using the Search API with size 0

Another approach to count documents in an index is to use the Search API with a size of 0. This method returns the total number of documents that match a query without returning the actual documents. Although this method is less efficient than the Count API, it can be useful in certain scenarios where you need additional information, such as aggregations.

Here’s an example of using the Search API with a size of 0 to count all documents in an index named `my_index`:

GET /my_index/_search
{
  "size": 0
}

Note that if your index contains more than 10000 documents and you need an exact count, you need to include `”track_total_hits”: true` as shown below (note that depending on your index size, this can be costly):

GET /my_index/_search
{
  "size": 0,
  "track_total_hits": true
}

To count documents that match a specific query, you can include the query in the request body:

GET /my_index/_search
{
  "size": 0,
  "query": {
    "match": {
      "field_name": "value"
    }
  }
}

Using the Cat API

The Cat API provides a human-readable format for various Elasticsearch operations, including counting documents in an index. The Cat API is useful for quick checks and debugging purposes.

Here’s an example of using the Cat API to count documents in an index named `my_index`:

GET /_cat/indices/my_index?v&h=docs.count

Beware, though, if you have nested documents, `docs.count` will also include the nested documents count in the result, which will differ from what you would get using the previous methods.

Comparing the Methods

Each method has its advantages and limitations:

1. **Count API**: The Count API is the most efficient method for counting documents in an index, as it returns only the count without the actual documents. It is suitable for both simple and complex queries.

2. **Search API with size 0**: Using the Search API with a size of 0 is less efficient than the Count API, but it can be useful in scenarios where you need additional information, such as aggregations. This method is suitable for complex queries and when additional information is required.
3. **Cat API**: The Cat API provides a human-readable format for counting documents in an index, making it useful for quick checks and debugging purposes. However, it may not be suitable for programmatic use due to its output format.

Monitoring and Optimizing Count Operations

Counting items in an Elasticsearch index can be resource-intensive, especially for large indices and complex queries. To ensure optimal performance, consider the following best practices:

1. **Use the Count API**: Whenever possible, use the Count API instead of the Search API with a size of 0, as it is more efficient.

2. **Optimize your queries**: Make sure your queries are optimized and use filters instead of queries when possible. Filters are faster and cacheable, which can improve performance.

3. **Cat API**: The Cat API provides a human-readable format for counting documents in an index, making it useful for quick checks and debugging purposes. However, if you have nested documents, the count will be the sum of the number of top-level documents and the number of nested documents.

Conclusion

In conclusion, counting items in an Elasticsearch index can be achieved using various methods, each with its advantages and limitations. By understanding these methods and following best practices, you can efficiently count items in your indices and ensure optimal performance for your Elasticsearch cluster.