elasticsearch/docs/reference/modules/indices/fielddata.asciidoc

[[modules-fielddata]]
=== Fielddata

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
    <<fielddata-circuit-breaker>>.

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

[float]
[[fielddata-monitoring]]
==== Monitoring field data

You can monitor memory usage for field data as well as the field data circuit
breaker using
<<cluster-nodes-stats,Nodes Stats API>>