Eager global ordinals

The eager_global_ordinals mapping parameter controls when global ordinals are built for a field. When enabled, global ordinals are computed during index refresh rather than “lazily” during query execution. This can improve performance for operations that rely on global ordinals, for example, sorting and aggregations on keyword fields. However, it may also increase index refresh times and memory usage.

Global ordinals represent a mapping from term values to integer identifiers and are used internally to quickly execute aggregations and sort operations. By loading them “eagerly,” the system reduces query latency at the cost of additional upfront processing during indexing.

By default, eager_global_ordinals are disabled, ensuring that the cluster is optimized for indexing speed.

Global ordinals are stored in the field data cache and consume heap memory. Fields with high cardinality can consume a large amount of heap memory. To prevent memory-related issues, it is important to carefully configure the field data circuit breaker settings.

When global ordinals are used

Global ordinals are used if a search includes any of the following:

• Bucket aggregations on keyword, ip, and flattened fields. This includes terms, composite, diversified_sampler, and significant_terms aggregations.
• Aggregations on text fields that require fielddata to be enabled.
• Parent/child queries using a join field, such as has_child queries or parent aggregations.

Enabling eager global ordinals on a field

The following request creates an index named products with eager_global_ordinals enabled:

PUT /products
{
  "mappings": {
    "properties": {
      "size": {
        "type": "keyword",
        "eager_global_ordinals": true
      }
    }
  }
}

The following request indexes a document:

PUT /products/_doc/1
{
  "size": "ABC123"
}

The following request runs a terms aggregation:

POST /products/_search
{
  "size": 0,
  "aggs": {
    "size_agg": {
      "terms": {
        "field": "size"
      }
    }
  }
}