Elasticsearch index.max_result_window Setting

The index.max_result_window setting in Elasticsearch controls the maximum number of results that can be returned from a single search query. It effectively limits the pagination depth for search results, preventing excessive memory usage and potential performance issues when dealing with large result sets.

• Default value: 10,000
• Possible values: Any positive integer
• Recommendations: Keep the default unless you have a specific need for deeper pagination and understand the performance implications

This setting defines the maximum value of from + size for a query. The from parameter specifies the starting point of the results, while size determines how many results to return. By default, Elasticsearch limits this sum to 10,000 to protect against queries that might consume excessive memory or cause performance degradation.

Example

To increase the index.max_result_window to allow for deeper pagination:

PUT /my_index/_settings
{
  "index.max_result_window": 20000
}

Reason for change: You need to paginate beyond 10,000 results for a specific use case.

Effects: Allows retrieval of results beyond the 10,000 limit, but may increase memory usage and query time for large result sets.

Common Issues and Misuses

• Setting an excessively high value can lead to out-of-memory errors or significantly slower query performance.
• Using deep pagination instead of more efficient alternatives like search after for real-time data.
• Relying on deep pagination for analytics or bulk data retrieval instead of using more appropriate methods like scroll API or aggregations.

Do's and Don'ts

Do's:

• Keep the default value unless absolutely necessary to change it.
• Consider alternative pagination methods like search_after for real-time data access.
• Use the scroll API for processing large amounts of data.
• Implement proper caching strategies if deep pagination is required.

Don'ts:

• Don't set an arbitrarily high value without understanding the performance implications.
• Avoid using deep pagination for analytics or reporting purposes.
• Don't rely on deep pagination for real-time data access in user interfaces.

Frequently Asked Questions

Q: Why is there a limit on the result window?
A: The limit exists to prevent excessive memory usage and maintain performance. Fetching and sorting large result sets can be resource-intensive and slow down the cluster.

Q: How can I retrieve more than 10,000 results?
A: For bulk data retrieval, use the scroll API. For real-time access to deep results, consider using the search_after parameter instead of offset-based pagination.

Q: Will increasing index.max_result_window affect all queries?
A: No, it only affects queries that attempt to access results beyond the current limit. Queries within the limit will behave as usual.

Q: Can index.max_result_window be set differently for each index?
A: Yes, this setting can be configured on a per-index basis, allowing you to have different limits for different indices based on their specific requirements.

Q: How does changing index.max_result_window impact cluster performance?
A: Increasing this value can lead to higher memory usage and longer query times, especially for queries that fetch a large number of results. It's important to monitor cluster performance after making changes to this setting.