What it does
The Script Score Query modifies the standard relevance score of matching documents by executing a script for each document. This script can access various document fields, query parameters, and even perform calculations to produce a custom score that is then combined with the original query score.
Syntax
{
"script_score": {
"query": { <wrapped query> },
"script": {
"source": "...",
"params": { ... }
}
}
}
For more details, refer to the official Elasticsearch documentation on Script Score Query.
Example Query
GET /my-index/_search
{
"query": {
"script_score": {
"query": {
"match": { "title": "elasticsearch" }
},
"script": {
"source": "doc['popularity'].value / 10 + _score",
"params": {
"a": 5,
"b": 1.2
}
}
}
}
}
This example combines the document's popularity field with the original text relevance score.
Common Issues
- Performance impact: Complex scripts can slow down query execution.
- Script errors: Syntax errors or logic issues in scripts can cause query failures.
- Field data loading: Ensure required fields are available for script execution.
- Security concerns: Be cautious with user-provided scripts to prevent potential vulnerabilities.
Best Practices
- Use script caching to improve performance for frequently used scripts.
- Prefer painless scripting language for better performance and security.
- Use params to pass variables to scripts for better reusability and performance.
- Monitor script execution times and optimize when necessary.
- Consider using function score query for simpler scoring adjustments when possible.
Frequently Asked Questions
Q: How does Script Score Query affect the overall relevance scoring?
A: The Script Score Query modifies the relevance score by multiplying the original query score with the script's output. This allows for custom boosting or penalizing of documents based on specific criteria.
Q: Can I access external data sources in a Script Score Query?
A: While it's not recommended for performance reasons, you can potentially access external data through Elasticsearch's HTTP client in scripts. However, it's generally better to preprocess and index such data.
Q: Is there a way to debug Script Score Queries?
A: Yes, you can use the explain API to see how scores are calculated. Additionally, you can add logging statements in your script for debugging purposes.
Q: Are there any limitations on what can be done in a Script Score Query?
A: While powerful, Script Score Queries are subject to the limitations of the scripting engine. There are restrictions on available libraries and operations for security reasons. Always refer to the latest documentation for current limitations.
Q: How can I optimize the performance of Script Score Queries?
A: To optimize performance, use script caching, minimize the complexity of your scripts, utilize params instead of hardcoding values, and ensure that fields used in scripts are efficiently stored and retrieved (e.g., using doc values when appropriate).
