The Script Query in Elasticsearch allows you to use scripts to create custom, dynamic queries. This powerful feature enables you to write complex logic for filtering documents based on runtime calculations or conditions that cannot be expressed using other query types.
Syntax
The basic syntax for a Script Query is:
{
"script": {
"script": {
"source": "SCRIPT_SOURCE",
"lang": "OPTIONAL_SCRIPT_LANGUAGE",
"params": {
"OPTIONAL_PARAMETERS": "VALUES"
}
}
}
}
For more details, refer to the official Elasticsearch documentation on Script Query.
Example Query
Here's an example of a Script Query that filters documents based on a custom condition:
GET /my-index/_search
{
"query": {
"script": {
"script": {
"source": "doc['price'].value < params.max_price && doc['in_stock'].value == true",
"lang": "painless",
"params": {
"max_price": 100
}
}
}
}
}
This query returns documents where the price is less than 100 and the item is in stock.
Common Issues
- Performance impact: Script queries can be slower than other query types, especially for large datasets.
- Script compilation: Frequent changes to scripts can lead to recompilation overhead.
- Security risks: Improperly secured scripts can pose security threats.
- Complexity: Writing and maintaining complex scripts can be challenging.
Best Practices
- Use script queries sparingly and only when necessary.
- Optimize scripts for performance by minimizing loops and complex operations.
- Leverage script caching to improve performance for frequently used scripts.
- Use parameterization to make scripts more flexible and reusable.
- Implement proper security measures, such as script sandboxing and access controls.
Frequently Asked Questions
Q: Can I use Script Query to access external resources?
A: Generally, no. For security reasons, Elasticsearch restricts scripts from accessing external resources. You should pass any required data as parameters to the script.
Q: How can I improve the performance of Script Queries?
A: Use script caching, optimize your script logic, and consider using stored scripts for frequently used queries. Also, limit the use of script queries to scenarios where other query types are insufficient.
Q: Are there alternatives to Script Query for custom scoring?
A: Yes, you can use function_score query or custom similarity plugins for advanced scoring without relying on scripts.
Q: What languages can I use in Script Queries?
A: Painless is the default and recommended scripting language for Elasticsearch. Other supported languages may include Lucene expressions and mustache templates, depending on your Elasticsearch version and configuration.
Q: How do I debug Script Queries?
A: Use the Explain API to see how your script is evaluated for specific documents. You can also log intermediate results within your script for debugging purposes.
