Elasticsearch Bucket Script Aggregation - Syntax, Example, and Tips

The Bucket Script Aggregation is a sibling pipeline aggregation that allows you to perform calculations across multiple buckets using scripts. This aggregation is particularly useful when you need to compute new values based on the metrics of multiple buckets.

Syntax

{
  "bucket_script": {
    "buckets_path": {
      "var1": "agg1",
      "var2": "agg2"
    },
    "script": "params.var1 / params.var2"
  }
}

For more details, refer to the official Elasticsearch documentation.

Example Usage

Here's an example that calculates the average price per unit for each product category:

{
  "aggs": {
    "categories": {
      "terms": {
        "field": "category"
      },
      "aggs": {
        "total_sales": {
          "sum": {
            "field": "sales"
          }
        },
        "total_units": {
          "sum": {
            "field": "units_sold"
          }
        },
        "avg_price_per_unit": {
          "bucket_script": {
            "buckets_path": {
              "sales": "total_sales",
              "units": "total_units"
            },
            "script": "params.sales / params.units"
          }
        }
      }
    }
  }
}

Common Issues

1. Script errors: Ensure that your script syntax is correct and all variables are properly defined in the buckets_path.
2. Division by zero: When dividing, make sure to handle cases where the denominator might be zero.
3. Missing buckets: The script will fail if any of the referenced buckets are missing. Use gap_policy to handle missing buckets.

Best Practices

1. Use meaningful variable names in your buckets_path to make scripts more readable.
2. Leverage Painless scripting language for complex calculations.
3. Consider using gap_policy to handle missing or incomplete buckets.
4. Monitor script execution times, as complex scripts can impact query performance.

Frequently Asked Questions

Q: Can I use Bucket Script Aggregation with nested aggregations?
A: Yes, you can use Bucket Script Aggregation with nested aggregations. Just make sure to properly reference the path to the nested metrics in your buckets_path.

Q: How do I handle division by zero in Bucket Script Aggregation?
A: You can use a conditional statement in your script to check for zero values. For example: params.denominator == 0 ? 0 : params.numerator / params.denominator

Q: Can I use Bucket Script Aggregation to perform calculations across different index patterns?
A: No, Bucket Script Aggregation operates on buckets within the same index pattern. For cross-index calculations, you might need to use other techniques like index aliases or join queries.

Q: Is there a limit to the complexity of scripts I can use in Bucket Script Aggregation?
A: While there's no strict limit, complex scripts can impact performance. It's recommended to keep scripts as simple as possible and consider moving very complex logic to a pre-processing step if needed.

Q: Can I use Bucket Script Aggregation in combination with other pipeline aggregations?
A: Yes, you can combine Bucket Script Aggregation with other pipeline aggregations. This allows for powerful and flexible analysis of your data across multiple dimensions.