Fielddata

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The field data cache is used mainly when sorting on or computing aggregations on a field. It loads all the field values to memory in order to provide fast document based access to those values. The field data cache can be expensive to build for a field, so its recommended to have enough memory to allocate it, and to keep it loaded.

The amount of memory used for the field data cache can be controlled using indices.fielddata.cache.size. Note: reloading the field data which does not fit into your cache will be expensive and perform poorly.

indices.fielddata.cache.size
The max size of the field data cache, eg 30% of node heap space, or an absolute value, eg 12GB. Defaults to unbounded. Also see Field data circuit breaker.
indices.fielddata.cache.expire
[preview] This functionality is in technical preview and may be changed or removed in a future release. Elastic will work to fix any issues, but features in technical preview are not subject to the support SLA of official GA features. A time based setting that expires field data after a certain time of inactivity. Defaults to -1. For example, can be set to 5m for a 5 minute expiry.

These are static settings which must be configured on every data node in the cluster.

Monitoring field data

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You can monitor memory usage for field data as well as the field data circuit breaker using Nodes Stats API