Field data

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The field data cache is used mainly when sorting on or aggregating 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.

Setting Description

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.

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.

Circuit Breaker

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Elasticsearch contains multiple circuit breakers used to prevent operations from causing an OutOfMemoryError. Each breaker specifies a limit for how much memory it can use. Additionally, there is a parent-level breaker that specifies the total amount of memory that can be used across all breakers.

The parent-level breaker can be configured with the following setting:

indices.breaker.total.limit
Starting limit for overall parent breaker, defaults to 70% of JVM heap

All circuit breaker settings can be changed dynamically using the cluster update settings API.

Field data circuit breaker

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The field data circuit breaker allows Elasticsearch to estimate the amount of memory a field will require to be loaded into memory. It can then prevent the field data loading by raising an exception. By default the limit is configured to 60% of the maximum JVM heap. It can be configured with the following parameters:

indices.breaker.fielddata.limit
Limit for fielddata breaker, defaults to 60% of JVM heap
indices.breaker.fielddata.overhead
A constant that all field data estimations are multiplied with to determine a final estimation. Defaults to 1.03

Request circuit breaker

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The request circuit breaker allows Elasticsearch to prevent per-request data structures (for example, memory used for calculating aggregations during a request) from exceeding a certain amount of memory.

indices.breaker.request.limit
Limit for request breaker, defaults to 40% of JVM heap
indices.breaker.request.overhead
A constant that all request estimations are multiplied with to determine a final estimation. Defaults to 1

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