What is index.warmer.enabled doing?


I’m looking for an explanation or documentation what the option index.warmer.enabled is toggling. When I set this option to false, I see the following changes in my ES clusters:

  • Heap requirement goes down by about 15-20GB (from 90GB).
  • The crazy amount of warmer finished operations disappears.
  • About half CPU usage.
  • About half of total network traffice.

Best regards,


Please check out this issue [1], tldr; for the context, the data warmer is used for two things:

  • To load the global ordinals if eager_global_ordinals is set on the field.
  • To load the bitset filters for all nested fields present in the mapping.

[1] https://github.com/elastic/elasticsearch/issues/29529