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Circuit breaker settings

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Circuit breaker settings

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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.

Except where noted otherwise, these settings can be dynamically updated on a live cluster with the cluster-update-settings API.

For information about circuit breaker errors, see Circuit breaker errors.

Parent circuit breaker

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

indices.breaker.total.use_real_memory: (Static) Determines whether the parent breaker should take real memory usage into account (true) or only consider the amount that is reserved by child circuit breakers (false). Defaults to true.

indices.breaker.total.limit: (Dynamic) Starting limit for overall parent breaker. Defaults to 70% of JVM heap if indices.breaker.total.use_real_memory is false. If indices.breaker.total.use_real_memory is true, defaults to 95% of the JVM heap.

Field data circuit breaker

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The field data circuit breaker estimates the heap memory required to load a field into the field data cache. If loading the field would cause the cache to exceed a predefined memory limit, the circuit breaker stops the operation and returns an error.

indices.breaker.fielddata.limit: (Dynamic) Limit for fielddata breaker. Defaults to 40% of JVM heap.

indices.breaker.fielddata.overhead: (Dynamic) 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: (Dynamic) Limit for request breaker, defaults to 60% of JVM heap.

indices.breaker.request.overhead: (Dynamic) A constant that all request estimations are multiplied with to determine a final estimation. Defaults to 1.

In flight requests circuit breaker

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The in flight requests circuit breaker allows Elasticsearch to limit the memory usage of all currently active incoming requests on transport or HTTP level from exceeding a certain amount of memory on a node. The memory usage is based on the content length of the request itself. This circuit breaker also considers that memory is not only needed for representing the raw request but also as a structured object which is reflected by default overhead.

network.breaker.inflight_requests.limit: (Dynamic) Limit for in flight requests breaker, defaults to 100% of JVM heap. This means that it is bound by the limit configured for the parent circuit breaker.
network.breaker.inflight_requests.overhead: (Dynamic) A constant that all in flight requests estimations are multiplied with to determine a final estimation. Defaults to 2.

Accounting requests circuit breaker

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The accounting circuit breaker allows Elasticsearch to limit the memory usage of things held in memory that are not released when a request is completed. This includes things like the Lucene segment memory.

indices.breaker.accounting.limit: (Dynamic) Limit for accounting breaker, defaults to 100% of JVM heap. This means that it is bound by the limit configured for the parent circuit breaker.
indices.breaker.accounting.overhead: (Dynamic) A constant that all accounting estimations are multiplied with to determine a final estimation. Defaults to 1

Script compilation circuit breaker

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Slightly different than the previous memory-based circuit breaker, the script compilation circuit breaker limits the number of inline script compilations within a period of time.

See the "prefer-parameters" section of the scripting documentation for more information.

script.max_compilations_rate: (Dynamic) Limit for the number of unique dynamic scripts within a certain interval that are allowed to be compiled. Defaults to 150/5m, meaning 150 every 5 minutes.

If the cluster regularly hits the given max_compilation_rate, it’s possible the script cache is undersized, use Nodes Stats to inspect the number of recent cache evictions, script.cache_evictions_history and compilations script.compilations_history. If there are a large number of recent cache evictions or compilations, the script cache may be undersized, consider doubling the size of the script cache via the setting script.cache.max_size.

Regex circuit breaker

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Poorly written regular expressions can degrade cluster stability and performance. The regex circuit breaker limits the use and complexity of regex in Painless scripts.

script.painless.regex.enabled

(Static) Enables regex in Painless scripts. Accepts:

limited (Default): Enables regex but limits complexity using the script.painless.regex.limit-factor cluster setting.
true: Enables regex with no complexity limits. Disables the regex circuit breaker.
false: Disables regex. Any Painless script containing a regular expression returns an error.

script.painless.regex.limit-factor

(Static) Limits the number of characters a regular expression in a Painless script can consider. Elasticsearch calculates this limit by multiplying the setting value by the script input’s character length.

For example, the input foobarbaz has a character length of 9. If script.painless.regex.limit-factor is 6, a regular expression on foobarbaz can consider up to 54 (9 * 6) characters. If the expression exceeds this limit, it triggers the regex circuit breaker and returns an error.

Elasticsearch only applies this limit if script.painless.regex.enabled is limited.

EQL circuit breaker

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When a sequence query is executed, the node handling the query needs to keep some structures in memory, which are needed by the algorithm implementing the sequence matching. When large amounts of data need to be processed, and/or a large amount of matched sequences is requested by the user (by setting the size query param), the memory occupied by those structures could potentially exceed the available memory of the JVM. This would cause an OutOfMemory exception which would bring down the node.

To prevent this from happening, a special circuit breaker is used, which limits the memory allocation during the execution of a sequence query. When the breaker is triggered, an org.elasticsearch.common.breaker.CircuitBreakingException is thrown and a descriptive error message is returned to the user.

This circuit breaker can be configured using the following settings:

breaker.eql_sequence.limit

(Dynamic) The limit for circuit breaker used to restrict the memory utilisation during the execution of an EQL sequence query. This value is defined as a percentage of the JVM heap. Defaults to 50%. If the parent circuit breaker is set to a value less than 50%, this setting uses that value as its default instead.

breaker.eql_sequence.overhead

(Dynamic) A constant that sequence query memory estimates are multiplied by to determine a final estimate. Defaults to 1.

breaker.eql_sequence.type

(Static) Circuit breaker type. Valid values are:

memory (Default): The breaker limits memory usage for EQL sequence queries.
noop: Disables the breaker.

Machine learning circuit breaker

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breaker.model_inference.limit: (Dynamic) The limit for the trained model circuit breaker. This value is defined as a percentage of the JVM heap. Defaults to 50%. If the parent circuit breaker is set to a value less than 50%, this setting uses that value as its default instead.
breaker.model_inference.overhead: (Dynamic) A constant that all trained model estimations are multiplied by to determine a final estimation. See Circuit breaker settings. Defaults to 1.
breaker.model_inference.type: (Static) The underlying type of the circuit breaker. There are two valid options: noop and memory. noop means the circuit breaker does nothing to prevent too much memory usage. memory means the circuit breaker tracks the memory used by trained models and can potentially break and prevent OutOfMemory errors. The default value is memory.

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