Configuring Enhanced Aggregation for an OpenSearch Cluster

CSS OpenSearch clusters enhance aggregation performance in the face of large data volumes by leveraging vectorization and optimized clustering, enabling faster analytics and decision-making in complex situations.

How the Feature Works

Enhanced aggregation works by pre-sorting and physically clustering data using carefully selected sorting and clustering keys, thereby minimizing data scanning and computational overheads during aggregation.

Sorting key: A field (such as timestamps) used to physically order documents on disk, ensuring that documents with identical or similar sorting key values are stored contiguously.
Clustering key: A subset of fields from the sorting key that groups related documents into contiguous physical blocks. This way, aggregations can process contiguous data blocks, instead of scattered documents.

**Table 1** Common scenarios for enhanced aggregation
Scenario	Description
Aggregation of low-cardinality fields	Aggregates fields that have a small number of unique values. In this case, grouping is used. One example is counting the number of orders per city. A clustering operation can easily achieve this purpose.
Aggregation of high-cardinality fields	Aggregates fields that have a large number of unique values. Histogram aggregation is typically used. One example is counting the hourly visits. A clustering key can be used to accelerate data aggregation by a specified scope or range.
Hybrid aggregation of low- and high-cardinality fields	Groups and aggregates low-cardinality fields first (for example, orders per city), and then creates a histogram using high-cardinality fields (for example, timestamps). Multi-level clustering improves the efficiency of hybrid queries.

Constraints

Only OpenSearch 2.19.0 clusters support this feature.

Aggregation of Low-Cardinality Fields

Generally, low-cardinality fields use grouping as a way of aggregation. With appropriate sorting keys, grouping prepares the data for batch vectorization.

For example, to aggregate two low-cardinality fields city and product, perform the following steps:

Run the following command to set the index testindex:

PUT testindex
{
  "mappings": {
    "properties": {
      "date": {
        "type": "date",
        "format": "yyyy-MM-dd"
      },
      "city": {
        "type": "keyword"
      },
      "product": {
        "type": "keyword"
      },
      "trade": {
        "type": "double"
      }
    }
  },
  "settings": {
    "index": {
      "search": {
        "turbo": {
          "enabled": "true" 
        }
      },
      "sort": {
        "field": [
          "city",
          "product"
        ]
      },
      "cluster": {
        "field": [
          "city",
          "product"
        ]
      }
    }
  }
}

**Table 2** Parameters for low-cardinality field aggregation
Parameter	Type	Description
index.search.turbo.enabled	Boolean	Whether to enable enhanced aggregation. Normally, enhanced aggregation must be enabled where aggregations are used. The value can be: false (default): Disable enhanced aggregation. true: Enable enhanced aggregation.
index.sort.field	Array of strings	Specify sorting keys. Sorting keys are fields used to sequence or rank documents. You can specify one or multiple fields as sorting keys. When multiple fields are specified, they will apply in the sequence in which they are specified. Documents are first ranked by the first field, then the initial result set is ranked by the second field, and so on. Value range: The value must be fields contained in the index.
index.cluster.field	Array of strings	Specify clustering keys. Clustering keys determine which documents are collected into the same clusters. During an aggregation operation, documents in the same cluster can be processed in batches, significantly enhancing aggregation performance. Constraint: The clustering keys must be a subset of the sorting keys. Value range: The value must be fields contained in the index.

Run the following command to import sample data.

PUT /_bulk
{ "index": { "_index": "testindex", "_id": "1" } }
{ "date": "2025-01-01", "city": "cityA", "product": "books", "trade": 3000.0}
{ "index": { "_index": "testindex", "_id": "2" } }
{ "date": "2025-01-02", "city": "cityA", "product": "books", "trade": 1000.0}
{ "index": { "_index": "testindex", "_id": "3" } }
{ "date": "2025-01-01", "city": "cityA", "product": "bottles", "trade": 100.0}
{ "index": { "_index": "testindex", "_id": "4" } }
{ "date": "2025-01-02", "city": "cityA", "product": "bottles", "trade": 300.0}
{ "index": { "_index": "testindex", "_id": "5" } }
{ "date": "2025-01-01", "city": "cityB", "product": "books", "trade": 7000.0}
{ "index": { "_index": "testindex", "_id": "6" } }
{ "date": "2025-01-02", "city": "cityB", "product": "books", "trade": 1000.0}

Run the following query command to aggregate low-cardinality fields.

POST testindex/_search
{
  "size": 0,
  "aggs": {
    "groupby_city": {
      "terms": {
        "field": "city"
      },
      "aggs": {
        "groupby_product": {
          "terms": {
            "field": "product"
          },
          "aggs": {
            "avg_trade": {
              "avg": {
                "field": "trade"
              }
            }
          }
        }
      }
    }
  }
}

Aggregation of High-Cardinality Fields

High-cardinality fields commonly use histogram aggregation, which facilitates data processing per range or scope.

For example, to aggregate the typical high-cardinality field date, perform the following steps:

Run the following command to set the index testindex:

PUT testindex
{
  "mappings": {
    "properties": {
      "timestamp": {
        "type": "date",
        "format": "yyyy-MM-dd"
      },
      "score": {
        "type": "double"
      }
    }
  },
  "settings": {
    "index": {
      "search": {
        "turbo": {
          "enabled": "true" 
        }
      },
      "sort": {
        "field": [
          "timestamp"
        ]
      }
    }
  }
}

**Table 3** Parameters for high-cardinality field aggregation
Parameter	Type	Description
index.search.turbo.enabled	Boolean	Whether to enable enhanced aggregation. Normally, enhanced aggregation must be enabled where aggregations are used. The value can be: false (default): Disable enhanced aggregation. true: Enable enhanced aggregation.
index.sort.field	Array of strings	Specify sorting keys. Sorting keys are fields used to sequence or rank documents. You can specify one or multiple fields as sorting keys. When multiple fields are specified, they will apply in the sequence in which they are specified. Documents are first ranked by the first field, then the initial result set is ranked by the second field, and so on. Value range: The value must be fields contained in the index.

Run the following command to import sample data.

PUT /_bulk
{ "index": { "_index": "testindex", "_id": "1" } }
{ "date": "2025-01-01", "score": "12.0"}
{ "index": { "_index": "testindex", "_id": "2" } }
{ "date": "2025-01-02","score": "24.0"}
{ "index": { "_index": "testindex", "_id": "3" } }
{ "date": "2025-01-01","score": "53.0"}
{ "index": { "_index": "testindex", "_id": "4" } }
{ "date": "2025-01-02", "score": "22.0"}
{ "index": { "_index": "testindex", "_id": "5" } }
{ "date": "2025-01-01", "score": "99.0"}
{ "index": { "_index": "testindex", "_id": "6" } }
{ "date": "2025-01-02","score": "26.0"}

Run the following query command to aggregate high-cardinality fields.

This query groups the date field using a histogram and then calculates the average score.

POST testindex/_search?pretty
{
  "size": 0,
  "aggs": {
    "groupbytime": {
      "date_histogram": {
        "field": "date",
        "calendar_interval": "day"
      },
      "aggs": {
        "avg_score": {
          "avg": {
            "field": "score"
          }
        }
      }
    }
  }
}

Hybrid Aggregation of Low- and High-Cardinality Fields

Where low-cardinality and high-cardinality fields are mixed, first groups and aggregates low-cardinality fields, and then aggregates high-cardinality fields using histograms.

For example, to first group the low-cardinality field city, then group the low-cardinality field product, and then group the high-cardinality field date into a histogram, perform the following steps:

Run the following command to set the index testindex:

PUT testindex
{
  "mappings": {
    "properties": {
      "date": {
        "type": "date",
        "format": "yyyy-MM-dd"
      },
      "city": {
        "type": "keyword"
      },
      "product": {
        "type": "keyword"
      },
      "trade": {
        "type": "double"
      }
    }
  },
  "settings": {
    "index": {
      "search": {
        "turbo": {
          "enabled": "true"
        }
      },
      "sort": { 
        "field": [
          "city",
          "product",
          "date"
        ]
      },
      "cluster": {
        "field": [
          "city",
          "product"
        ]
      }
    }
  }
}

**Table 4** Parameters for hybrid aggregation of low- and high-cardinality fields
Parameter	Type	Description
index.search.turbo.enabled	Boolean	Whether to enable enhanced aggregation. Normally, enhanced aggregation must be enabled where aggregations are used. The value can be: false (default): Disable enhanced aggregation. true: Enable enhanced aggregation.
index.sort.field	Array of strings	Specify sorting keys. Sorting keys are fields used to sequence or rank documents. You can specify one or multiple fields as sorting keys. When multiple fields are specified, they will apply in the sequence in which they are specified. Documents are first ranked by the first field, then the initial result set is ranked by the second field, and so on. Constraint: High-cardinality fields must be among the sorting keys, and must follow the last low-cardinality field. Value range: The value must be fields contained in the index.
index.cluster.field	Array of strings	Specify clustering keys. Clustering keys determine which documents are collected into the same clusters. During an aggregation operation, documents in the same cluster can be processed in batches, significantly enhancing aggregation performance. Constraint: The clustering keys must be a subset of the sorting keys. Value range: The value must be fields contained in the index.

Run the following command to import sample data.

PUT /_bulk
{ "index": { "_index": "testindex", "_id": "1" } }
{ "date": "2025-01-01", "city": "cityA", "product": "books", "trade": 3000.0}
{ "index": { "_index": "testindex", "_id": "2" } }
{ "date": "2025-01-02", "city": "cityA", "product": "books", "trade": 1000.0}
{ "index": { "_index": "testindex", "_id": "3" } }
{ "date": "2025-01-01", "city": "cityA", "product": "bottles", "trade": 100.0}
{ "index": { "_index": "testindex", "_id": "4" } }
{ "date": "2025-01-02", "city": "cityA", "product": "bottles", "trade": 300.0}
{ "index": { "_index": "testindex", "_id": "5" } }
{ "date": "2025-01-01", "city": "cityB", "product": "books", "trade": 7000.0}
{ "index": { "_index": "testindex", "_id": "6" } }
{ "date": "2025-01-02", "city": "cityB", "product": "books", "trade": 1000.0}

Run the following query command to perform a hybrid aggregation of low- and high-cardinality fields.

POST testindex/_search
{
  "size": 0,
  "aggs": {
    "groupby_region": {
      "terms": {
        "field": "city"
      },
      "aggs": {
        "groupby_host": {
          "terms": {
            "field": "product"
          },
          "aggs": {
            "groupby_timestamp": {
              "date_histogram": {
                "field": "date",
                "interval": "day"
              },
              "aggs": {
                "avg_score": {
                  "avg": {
                    "field": "trade"
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

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