Cluster-wide settings

All current applied cluster settings can be read by querying the sys.cluster.settings column. Most cluster settings can be changed at runtime. This is documented at each setting.

Non-runtime cluster-wide settings

Cluster wide settings which cannot be changed at runtime need to be specified in the configuration of each node in the cluster.

Caution

Cluster settings specified via node configurations are required to be exactly the same on every node in the cluster for proper operation of the cluster.

Collecting stats

stats.enabled

Default: true

Runtime: yes

A boolean indicating whether or not to collect statistical information about the cluster.

Caution

The collection of statistical information incurs a slight performance penalty, as details about every job and operation across the cluster will cause data to be inserted into the corresponding system tables.

stats.jobs_log_size

Default: 10000

Runtime: yes

The maximum number of job records kept to be kept in the sys.jobs_log table on each node.

A job record corresponds to a single SQL statement to be executed on the cluster. These records are used for performance analytics. A larger job log produces more comprehensive stats, but uses more RAM.

Older job records are deleted as newer records are added, once the limit is reached.

Setting this value to 0 disables collecting job information.

stats.jobs_log_expiration

Default: 0s (disabled)

Runtime: yes

The job record expiry time in seconds.

Job records in the sys.jobs_log table are periodically cleared if they are older than the expiry time. This setting overrides stats.jobs_log_size.

If the value is set to 0, time based log entry eviction is disabled.

Note

If both the stats.operations_log_size and stats.operations_log_expiration settings are disabled, jobs will not be recorded.

stats.jobs_log_filter

Default: true (Include everything)

Runtime: yes

An :ref:expression <gloss-expression>` to determine if a job should be recorded into sys.jobs_log. The expression must evaluate to a boolean. If it evaluates to true the statement will show up in sys.jobs_log until it’s evicted due to one of the other rules. (expiration or size limit reached).

The expression may reference all columns contained in sys.jobs_log. A common use case is to include only jobs that took a certain amount of time to execute:

cr> SET GLOBAL "stats.jobs_log_filter" = 'ended - started > 100';

stats.jobs_log_persistent_filter

Default: false (Include nothing)

Runtime: yes

An expression to determine if a job should also be recorded to the regular CrateDB log. Entries that match this filter will be logged under the StatementLog logger with the INFO level.

This is similar to stats.jobs_log_filter except that these entries are persisted to the log file. This should be used with caution and shouldn’t be set to an expression that matches many queries as the logging operation will block on IO and can therefore affect performance.

A common use case is to use this for slow query logging.

stats.operations_log_size

Default: 10000

Runtime: yes

The maximum number of operations records to be kept in the sys.operations_log table on each node.

A job consists of one or more individual operations. Operations records are used for performance analytics. A larger operations log produces more comprehensive stats, but uses more RAM.

Older operations records are deleted as newer records are added, once the limit is reached.

Setting this value to 0 disables collecting operations information.

stats.operations_log_expiration

Default: 0s (disabled)

Runtime: yes

Entries of sys.operations_log are cleared by a periodically job when they are older than the specified expire time. This setting overrides stats.operations_log_size. If the value is set to 0 the time based log entry eviction is disabled.

Note

If both setttings stats.operations_log_size and stats.operations_log_expiration are disabled, no job information will be collected.

stats.service.interval

Default: 24h

Runtime: yes

Defines the refresh interval to refresh tables statistics used to produce optimal query execution plans.

This field expects a time value either as a bigint or double precision or alternatively as a string literal with a time suffix (ms, s, m, h, d, w).

If the value provided is 0 then the refresh is disabled.

Caution

Using a very small value can cause a high load on the cluster.

Shard limits

cluster.max_shards_per_node

Default: 1000

Runtime: yes

The maximum amount of shards per node.

Any operations that would result in the creation of additional shard copies that would exceed this limit are rejected.

For example. If you have 999 shards in the current cluster and you try to create a new table, the create table operation will fail.

Similarly, if a write operation would lead to the creation of a new partition, the statement will fail.

Each shard on a node requires some memory and increases the size of the cluster state. Having too many shards per node will impact the clusters stability and it is therefore discouraged to raise the limit above 1000.

Usage data collector

The settings of the Usage Data Collector are read-only and cannot be set during runtime. Please refer to Usage Data Collector to get further information about its usage.

udc.enabled

Default: true

Runtime: no

true: Enables the Usage Data Collector.

false: Disables the Usage Data Collector.

udc.initial_delay

Default: 10m

Runtime: no

The delay for first ping after start-up.

This field expects a time value either as a bigint or double precision or alternatively as a string literal with a time suffix (ms, s, m, h, d, w).

udc.interval

Default: 24h

Runtime: no

The interval a UDC ping is sent.

• This field expects a time value either as a bigint or

  double precision or alternatively as a string literal with a time suffix (ms, s, m, h, d, w).

udc.url

Default: https://udc.crate.io

Runtime: no

The URL the ping is sent to.

Graceful stop

By default, when the CrateDB process stops it simply shuts down, possibly making some shards unavailable which leads to a red cluster state and lets some queries fail that required the now unavailable shards. In order to safely shutdown a CrateDB node, the graceful stop procedure can be used.

The following cluster settings can be used to change the shutdown behaviour of nodes of the cluster:

cluster.graceful_stop.min_availability

Default: primaries

Runtime: yes

Allowed values: none | primaries | full

none: No minimum data availability is required. The node may shut down even if records are missing after shutdown.

primaries: At least all primary shards need to be available after the node has shut down. Replicas may be missing.

full: All records and all replicas need to be available after the node has shut down. Data availability is full.

Note

This option is ignored if there is only 1 node in a cluster!

cluster.graceful_stop.timeout

Default: 2h

Runtime: yes

Defines the maximum waiting time in milliseconds for the reallocation process to finish. The force setting will define the behaviour when the shutdown process runs into this timeout.

The timeout expects a time value either as a bigint or double precision or alternatively as a string literal with a time suffix (ms, s, m, h, d, w).

cluster.graceful_stop.force

Default: false

Runtime: yes

Defines whether graceful stop should force stopping of the node if it runs into the timeout which is specified with the cluster.graceful_stop.timeout setting.

Bulk operations

SQL DML Statements involving a huge amount of rows like COPY FROM, INSERT or UPDATE can take an enormous amount of time and resources. The following settings change the behaviour of those queries.

bulk.request_timeout

Default: 1m

Runtime: yes

Defines the timeout of internal shard-based requests involved in the execution of SQL DML Statements over a huge amount of rows.

Discovery

Data sharding and work splitting are at the core of CrateDB. This is how we manage to execute very fast queries over incredibly large datasets. In order for multiple CrateDB nodes to work together a cluster needs to be formed. The process of finding other nodes with which to form a cluster is called discovery. Discovery runs when a CrateDB node starts and when a node is not able to reach the master node and continues until a master node is found or a new master node is elected.

discovery.seed_hosts

Default: 127.0.0.1

Runtime: no

In order to form a cluster with CrateDB instances running on other nodes a list of seed master-eligible nodes needs to be provided. This setting should normally contain the addresses of all the master-eligible nodes in the cluster. In order to seed the discovery process the nodes listed here must be live and contactable. This setting contains either an array of hosts or a comma-delimited string. By default a node will bind to the available loopback and scan for local ports between 4300 and 4400 to try to connect to other nodes running on the same server. This default behaviour provides local auto clustering without any configuration. Each value should be in the form of host:port or host (where port defaults to the setting transport.tcp.port).

Note

IPv6 hosts must be bracketed.

cluster.initial_master_nodes

Default: not set

Runtime: no

Contains a list of node names, full-qualified hostnames or IP addresses of the master-eligible nodes which will vote in the very first election of a cluster that’s bootstrapping for the first time. By default this is not set, meaning it expects this node to join an already formed cluster. In development mode, with no discovery settings configured, this step is performed by the nodes themselves, but this auto-bootstrapping is designed to aim development and is not safe for production. In production you must explicitly list the names or IP addresses of the master-eligible nodes whose votes should be counted in the very first election.

discovery.type

Default: zen

Runtime: no

Allowed values: zen | single-node

Specifies whether CrateDB should form a multiple-node cluster. By default, CrateDB discovers other nodes when forming a cluster and allows other nodes to join the cluster later. If discovery.type is set to single-node, CrateDB forms a single-node cluster and the node won’t join any other clusters. This can be useful for testing. It is not recommend to use this for production setups. The single-node mode also skips bootstrap checks.

Caution

If a node is started without any initial_master_nodes or a discovery_type set to single-node (e.g., the default configuration), it will never join a cluster even if the configuration is subsequently changed.

It is possible to force the node to forget its current cluster state by using the crate-node CLI tool. However, be aware that this may result in data loss.

Unicast host discovery

As described above, CrateDB has built-in support for statically specifying a list of addresses that will act as the seed nodes in the discovery process using the discovery.seed_hosts setting.

CrateDB also has support for several different mechanisms of seed nodes discovery. Currently there are three other discovery types: via DNS, via EC2 API and via Microsoft Azure mechanisms.

When a node starts up with one of these discovery types enabled, it performs a lookup using the settings for the specified mechanism listed below. The hosts and ports retrieved from the mechanism will be used to generate a list of unicast hosts for node discovery.

The same lookup is also performed by all nodes in a cluster whenever the master is re-elected (see Cluster Meta Data).

discovery.seed_providers

Default: not set

Runtime: no

Allowed values: srv, ec2, azure

See also: Discovery.

Discovery via DNS

Crate has built-in support for discovery via DNS. To enable DNS discovery the discovery.seed_providers setting needs to be set to srv.

The order of the unicast hosts is defined by the priority, weight and name of each host defined in the SRV record. For example:

_crate._srv.example.com. 3600 IN SRV 2 20 4300 crate1.example.com.
_crate._srv.example.com. 3600 IN SRV 1 10 4300 crate2.example.com.
_crate._srv.example.com. 3600 IN SRV 2 10 4300 crate3.example.com.

would result in a list of discovery nodes ordered like:

crate2.example.com:4300, crate3.example.com:4300, crate1.example.com:4300

discovery.srv.query

Runtime: no

The DNS query that is used to look up SRV records, usually in the format _service._protocol.fqdn If not set, the service discovery will not be able to look up any SRV records.

discovery.srv.resolver

Runtime: no

The hostname or IP of the DNS server used to resolve DNS records. If this is not set, or the specified hostname/IP is not resolvable, the default (system) resolver is used.

Optionally a custom port can be specified using the format hostname:port.

Discovery on Amazon EC2

CrateDB has built-in support for discovery via the EC2 API. To enable EC2 discovery the discovery.seed_providers settings needs to be set to ec2.

discovery.ec2.access_key

Runtime: no

The access key ID to identify the API calls.

discovery.ec2.secret_key

Runtime: no

The secret key to identify the API calls.

Following settings control the discovery:

discovery.ec2.groups

Runtime: no

A list of security groups; either by ID or name. Only instances with the given group will be used for unicast host discovery.

discovery.ec2.any_group

Default: true

Runtime: no

Defines whether all (false) or just any (true) security group must be present for the instance to be used for discovery.

discovery.ec2.host_type

Default: private_ip

Runtime: no

Allowed values: private_ip, public_ip, private_dns, public_dns

Defines via which host type to communicate with other instances.

discovery.ec2.availability_zones

Runtime: no

A list of availability zones. Only instances within the given availability zone will be used for unicast host discovery.

discovery.ec2.tag.<name>

Runtime: no

EC2 instances for discovery can also be filtered by tags using the discovery.ec2.tag. prefix plus the tag name.

E.g. to filter instances that have the environment tags with the value dev your setting will look like: discovery.ec2.tag.environment: dev.

discovery.ec2.endpoint

Runtime: no

If you have your own compatible implementation of the EC2 API service you can set the endpoint that should be used.

Discovery on Microsoft Azure

CrateDB has built-in support for discovery via the Azure Virtual Machine API. To enable Azure discovery set the discovery.seed_providers setting to azure.

cloud.azure.management.resourcegroup.name

Runtime: no

The name of the resource group the CrateDB cluster is running on.

All nodes need to be started within the same resource group.

cloud.azure.management.subscription.id

Runtime: no

The subscription ID of your Azure account.

You can find the ID on the Azure Portal.

cloud.azure.management.tenant.id

Runtime: no

The tenant ID of the Active Directory application.

cloud.azure.management.app.id

Runtime: no

The application ID of the Active Directory application.

cloud.azure.management.app.secret

Runtime: no

The password of the Active Directory application.

discovery.azure.method

Default: vnet

Runtime: no

Allowed values: vnet | subnet

Defines the scope of the discovery. vnet will discover all VMs within the same virtual network (default), subnet will discover all VMs within the same subnet of the CrateDB instance.

Routing allocation

cluster.routing.allocation.enable

Default: all

Runtime: yes

Allowed values: all | none | primaries | new_primaries

all allows all shard allocations, the cluster can allocate all kinds of shards.

none allows no shard allocations at all. No shard will be moved or created.

primaries only primaries can be moved or created. This includes existing primary shards.

new_primaries allows allocations for new primary shards only. This means that for example a newly added node will not allocate any replicas. However it is still possible to allocate new primary shards for new indices. Whenever you want to perform a zero downtime upgrade of your cluster you need to set this value before gracefully stopping the first node and reset it to all after starting the last updated node.

Note

This allocation setting has no effect on the recovery of primary shards! Even when cluster.routing.allocation.enable is set to none, nodes will recover their unassigned local primary shards immediatelly after restart.

cluster.routing.rebalance.enable

Default: all

Runtime: yes

Allowed values: all | none | primaries | replicas

Enables or disables rebalancing for different types of shards:

• all allows shard rebalancing for all types of shards.

• none disables shard rebalancing for any types.

• primaries allows shard rebalancing only for primary shards.

• replicas allows shard rebalancing only for replica shards.

cluster.routing.allocation.allow_rebalance

Default: indices_all_active

Runtime: yes

Allowed values: always | indices_primary_active | indices_all_active

Defines when rebalancing will happen based on the total state of all the indices shards in the cluster.

Defaults to indices_all_active to reduce chatter during initial recovery.

cluster.routing.allocation.cluster_concurrent_rebalance

Default: 2

Runtime: yes

Defines how many concurrent rebalancing tasks are allowed across all nodes.

cluster.routing.allocation.node_initial_primaries_recoveries

Default: 4

Runtime: yes

Defines how many concurrent primary shard recoveries are allowed on a node.

Since primary recoveries use data that is already on disk (as opposed to inter-node recoveries), recovery should be fast and so this setting can be higher than node_concurrent_recoveries.

cluster.routing.allocation.node_concurrent_recoveries

Default: 2

Runtime: yes

Defines how many concurrent recoveries are allowed on a node.

Shard balancing

You can configure how CrateDB attempts to balance shards across a cluster by specifying one or more property weights. CrateDB will consider a cluster to be balanced when no further allowed action can bring the weighted properties of each node closer together.

Note

Balancing may be restricted by other settings (e.g., attribute-based and disk-based shard allocation).

cluster.routing.allocation.balance.shard

Default: 0.45f

Runtime: yes

Defines the weight factor for shards allocated on a node (float). Raising this raises the tendency to equalize the number of shards across all nodes in the cluster.

cluster.routing.allocation.balance.index

Default: 0.55f

Runtime: yes

Defines a factor to the number of shards per index allocated on a specific node (float). Increasing this value raises the tendency to equalize the number of shards per index across all nodes in the cluster.

cluster.routing.allocation.balance.threshold

Default: 1.0f

Runtime: yes

Minimal optimization value of operations that should be performed (non negative float). Increasing this value will cause the cluster to be less aggressive about optimising the shard balance.

Attribute-based shard allocation

You can control how shards are allocated to specific nodes by setting custom attributes on each node (e.g., server rack ID or node availability zone). After doing this, you can define cluster-wide attribute awareness and then configure cluster-wide attribute filtering.

See also

For an in-depth example of using custom node attributes, check out the multi-zone setup how-to guide.

Cluster-wide attribute awareness

To make use of custom attributes for attribute-based shard allocation, you must configure cluster-wide attribute awareness.

cluster.routing.allocation.awareness.attributes

Runtime: no

You may define custom node attributes which can then be used to do awareness based on the allocation of a shard and its replicas.

For example, let’s say we want to use an attribute named rack_id. We start two nodes with node.attr.rack_id set to rack_one. Then we create a single table with five shards and one replica. The table will be fully deployed on the current nodes (five shards and one replica each, making a total of 10 shards).

Now, if we start two more nodes with node.attr.rack_id set to rack_two, CrateDB will relocate shards to even out the number of shards across the nodes. However, a shard and its replica will not be allocated to nodes sharing the same rack_id value.

The awareness.attributes setting supports using several values.

cluster.routing.allocation.awareness.force.*.values

Runtime: no

Attributes on which shard allocation will be forced. Here, * is a placeholder for the awareness attribute, which can be configured using the cluster.routing.allocation.awareness.attributes setting.

For example, let’s say we configured forced shard allocation for an awareness attribute named zone with values set to zone1, zone2. Start two nodes with node.attr.zone set to zone1. Then, create a table with five shards and one replica. The table will be created, but only five shards will be allocated (with no replicas). The replicas will only be allocated when when we start one or more nodes with node.attr.zone set to zone2.

Cluster-wide attribute filtering

To control how CrateDB uses custom attributes for attribute-based shard allocation, you must configure cluster-wide attribute filtering.

Note

CrateDB will retroactively enforce filter definitions. If a new filter would prevent newly created matching shards from being allocated to a node, CrateDB would also move any existing matching shards away from that node.

cluster.routing.allocation.include.*

Runtime: yes

Only allocate shards on nodes where one of the specified values matches the attribute.

For example:

cluster.routing.allocation.include.zone: "zone1,zone2"`

cluster.routing.allocation.exclude.*

Runtime: yes

Only allocate shards on nodes where none of the specified values matches the attribute.

For example:

cluster.routing.allocation.exclude.zone: "zone1"

cluster.routing.allocation.require.*

Runtime: yes

Used to specify a number of rules, which all MUST match for a node in order to allocate a shard on it. This is in contrast to include which will include a node if ANY rule matches.

Disk-based shard allocation

cluster.routing.allocation.disk.threshold_enabled

Default: true

Runtime: yes

Prevent shard allocation on nodes depending of the disk usage.

cluster.routing.allocation.disk.watermark.low

Default: 85%

Runtime: yes

Defines the lower disk threshold limit for shard allocations. New shards will not be allocated on nodes with disk usage greater than this value. It can also be set to an absolute bytes value (like e.g. 500mb) to prevent the cluster from allocating new shards on node with less free disk space than this value.

cluster.routing.allocation.disk.watermark.high

Default: 90%

Runtime: yes

Defines the higher disk threshold limit for shard allocations. The cluster will attempt to relocate existing shards to another node if the disk usage on a node rises above this value. It can also be set to an absolute bytes value (like e.g. 500mb) to relocate shards from nodes with less free disk space than this value.

cluster.routing.allocation.disk.watermark.flood_stage

Default: 95%

Runtime: yes

Defines the threshold on which CrateDB enforces a read-only block on every index that has at least one shard allocated on a node with at least one disk exceeding the flood stage.

Note

Read-only blocks are not automatically removed from the indices if the disk space is freed and the threshold is undershot. To remove the block, execute ALTER TABLE ... SET ("blocks.read_only_allow_delete" = FALSE) for affected tables (see blocks.read_only_allow_delete).

cluster.routing.allocation.disk.watermark settings may be defined as percentages or bytes values. However, it is not possible to mix the value types.

By default, the cluster will retrieve information about the disk usage of the nodes every 30 seconds. This can also be changed by setting the cluster.info.update.interval setting.

Note

The watermark settings are also used for the Routing allocation disk watermark low and Routing allocation disk watermark high node check.

Setting cluster.routing.allocation.disk.threshold_enabled to false will disable the allocation decider, but the node checks will still be active and warn users about running low on disk space.

cluster.routing.allocation.total_shards_per_node

Default: -1

Runtime: yes

Limits the number of shards that can be allocated per node. A value of -1 means unlimited.

Setting this to 1000, for example, will prevent CrateDB from assigning more than 1000 shards per node. A node with 1000 shards would be excluded from allocation decisions and CrateDB would attempt to allocate shards to other nodes, or leave shards unassigned if no suitable node can be found.

Recovery

indices.recovery.max_bytes_per_sec

Default: 40mb

Runtime: yes

Specifies the maximum number of bytes that can be transferred during shard recovery per seconds. Limiting can be disabled by setting it to 0. This setting allows to control the network usage of the recovery process. Higher values may result in higher network utilization, but also faster recovery process.

indices.recovery.retry_delay_state_sync

Default: 500ms

Runtime: yes

Defines the time to wait after an issue caused by cluster state syncing before retrying to recover.

indices.recovery.retry_delay_network

Default: 5s

Runtime: yes

Defines the time to wait after an issue caused by the network before retrying to recover.

indices.recovery.internal_action_timeout

Default: 15m

Runtime: yes

Defines the timeout for internal requests made as part of the recovery.

indices.recovery.internal_action_long_timeout

Default: 30m

Runtime: yes

Defines the timeout for internal requests made as part of the recovery that are expected to take a long time. Defaults to twice internal_action_timeout.

indices.recovery.recovery_activity_timeout

Default: 30m

Runtime: yes

Recoveries that don’t show any activity for more then this interval will fail. Defaults to internal_action_long_timeout.

indices.recovery.max_concurrent_file_chunks

Default: 2

Runtime: yes

Controls the number of file chunk requests that can be sent in parallel per recovery. As multiple recoveries are already running in parallel, controlled by cluster.routing.allocation.node_concurrent_recoveries, increasing this expert-level setting might only help in situations where peer recovery of a single shard is not reaching the total inbound and outbound peer recovery traffic as configured by indices.recovery.max_bytes_per_sec, but is CPU-bound instead, typically when using transport-level security or compression.

Memory management

memory.allocation.type

Default: on-heap

Runtime: yes

Supported values are on-heap and off-heap. This influences if memory is preferably allocated in the heap space or in the off-heap/direct memory region.

Setting this to off-heap doesn’t imply that the heap won’t be used anymore. Most allocations will still happen in the heap space but some operations will be allowed to utilize off heap buffers.

Warning

Using off-heap is considered experimental.

Query circuit breaker

The Query circuit breaker will keep track of the used memory during the execution of a query. If a query consumes too much memory or if the cluster is already near its memory limit it will terminate the query to ensure the cluster keeps working.

indices.breaker.query.limit

Default: 60%

Runtime: yes

Specifies the limit for the query breaker. Provided values can either be absolute values (interpreted as a number of bytes), byte sizes (eg. 1mb) or percentage of the heap size (eg. 12%). A value of -1 disables breaking the circuit while still accounting memory usage.

indices.breaker.query.overhead

Default: 1.00

Runtime: no

Caution

This setting is deprecated and has no effect.

Field data circuit breaker

These settings are deprecated and will be removed in CrateDB 5.0. They don’t have any effect anymore.

indices.breaker.fielddata.limit

Default: 60%

Runtime: yes

indices.breaker.fielddata.overhead

Default: 1.03

Runtime: yes

Request circuit breaker

The request circuit breaker allows an estimation of required heap memory per request. If a single request exceeds the specified amount of memory, an exception is raised.

indices.breaker.request.limit

Default: 60%

Runtime: yes

Specifies the JVM heap limit for the request circuit breaker.

indices.breaker.request.overhead

Default: 1.0

Runtime: yes

Caution

This setting is deprecated and has no effect.

Accounting circuit breaker

Tracks things that are held in memory independent of queries. For example the memory used by Lucene for segments.

indices.breaker.accounting.limit

Default: 100%

Runtime: yes

Specifies the JVM heap limit for the accounting circuit breaker

indices.breaker.accounting.overhead

Default: 1.0

Runtime: yes

Caution

This setting is deprecated and has no effect.

Stats circuit breakers

Settings that control the behaviour of the stats circuit breaker. There are two breakers in place, one for the jobs log and one for the operations log. For each of them, the breaker limit can be set.

stats.breaker.log.jobs.limit

Default: 5%

Runtime: yes

The maximum memory that can be used from CRATE_HEAP_SIZE for the sys.jobs_log table on each node.

When this memory limit is reached, the job log circuit breaker logs an error message and clears the sys.jobs_log table completely.

stats.breaker.log.operations.limit

Default: 5%

Runtime: yes

The maximum memory that can be used from CRATE_HEAP_SIZE for the sys.operations_log table on each node.

When this memory limit is reached, the operations log circuit breaker logs an error message and clears the sys.operations_log table completely.

Total circuit breaker

indices.breaker.total.limit

Default: 95%

Runtime: yes

The maximum memory that can be used by all aforementioned circuit breakers together.

Even if an individual circuit breaker doesn’t hit its individual limit, queries might still get aborted if several circuit breakers together would hit the memory limit configured in indices.breaker.total.limit.

Thread pools

Every node holds several thread pools to improve how threads are managed within a node. There are several pools, but the important ones include:

• write: For index, update and delete operations, defaults to fixed

• search: For count/search operations, defaults to fixed

• get: For queries on sys.shards and sys.nodes, defaults to fixed.

• refresh: For refresh operations, defaults to cache

thread_pool.<name>.type

Runtime: no

Allowed values: fixed | scaling

fixed holds a fixed size of threads to handle the requests. It also has a queue for pending requests if no threads are available.

scaling ensures that a thread pool holds a dynamic number of threads that are proportional to the workload.

Settings for fixed thread pools

If the type of a thread pool is set to fixed there are a few optional settings.

thread_pool.<name>.size

Runtime: no

Number of threads. The default size of the different thread pools depend on the number of available CPU cores.

thread_pool.<name>.queue_size

Default write: 200

Default search: 1000

Default get: 100

Runtime: no

Size of the queue for pending requests. A value of -1 sets it to unbounded.

Metadata

cluster.info.update.interval

Default: 30s

Runtime: yes

Defines how often the cluster collect metadata information (e.g. disk usages etc.) if no concrete event is triggered.

Metadata gateway

The following settings can be used to configure the behavior of the metadata gateway.

gateway.expected_nodes

Default: -1

Runtime: no

The setting gateway.expected_nodes defines the number of nodes that should be waited for until the cluster state is recovered immediately. The value of the setting should be equal to the number of nodes in the cluster, because you only want the cluster state to be recovered after all nodes are started.

gateway.recover_after_time

Default: 0ms

Runtime: no

The gateway.recover_after_time setting defines the time to wait before starting the recovery once the number of nodes defined in gateway.recover_after_nodes are started. The setting is relevant if gateway.recover_after_nodes is less than gateway.expected_nodes.

gateway.recover_after_nodes

Default: -1

Runtime: no

The gateway.recover_after_nodes setting defines the number of nodes that need to be started before the cluster state recovery will start. Ideally the value of the setting should be equal to the number of nodes in the cluster, because you only want the cluster state to be recovered once all nodes are started. However, the value must be bigger than the half of the expected number of nodes in the cluster.