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Thread Pool

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Thread Pool

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A node holds several thread pools in order to improve how threads memory consumption are managed within a node. Many of these pools also have queues associated with them, which allow pending requests to be held instead of discarded.

There are several thread pools, but the important ones include:

`index`	For index/delete operations. Defaults to `fixed` with a size of `# of available processors`, queue_size of `200`.
`search`	For count/search operations. Defaults to `fixed` with a size of `3x # of available processors`, queue_size of `1000`.
`suggest`	For suggest operations. Defaults to `fixed` with a size of `# of available processors`, queue_size of `1000`.
`get`	For get operations. Defaults to `fixed` with a size of `# of available processors`, queue_size of `1000`.
`bulk`	For bulk operations. Defaults to `fixed` with a size of `# of available processors`, queue_size of `50`.
`percolate`	For percolate operations. Defaults to `fixed` with a size of `# of available processors`, queue_size of `1000`.
`snapshot`	For snapshot/restore operations. Defaults to `scaling`, keep-alive `5m` with a size of `(# of available processors)/2`.
`warmer`	For segment warm-up operations. Defaults to `scaling` with a `5m` keep-alive.
`refresh`	For refresh operations. Defaults to `scaling` with a `5m` keep-alive.
`listener`	Mainly for java client executing of action when listener threaded is set to true. Default size of `(# of available processors)/2`, max at 10.

Changing a specific thread pool can be done by setting its type and specific type parameters, for example, changing the index thread pool to have more threads:

threadpool:
    index:
        type: fixed
        size: 30

you can update threadpool settings live using Cluster Update Settings.

Thread pool types

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The following are the types of thread pools that can be used and their respective parameters:

`cache`

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The cache thread pool is an unbounded thread pool that will spawn a thread if there are pending requests. Here is an example of how to set it:

threadpool:
    index:
        type: cached

`fixed`

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The fixed thread pool holds a fixed size of threads to handle the requests with a queue (optionally bounded) for pending requests that have no threads to service them.

The size parameter controls the number of threads, and defaults to the number of cores times 5.

The queue_size allows to control the size of the queue of pending requests that have no threads to execute them. By default, it is set to -1 which means its unbounded. When a request comes in and the queue is full, it will abort the request.

threadpool:
    index:
        type: fixed
        size: 30
        queue_size: 1000

Processors setting

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The number of processors is automatically detected, and the thread pool settings are automatically set based on it. Sometimes, the number of processors are wrongly detected, in such cases, the number of processors can be explicitly set using the processors setting.

In order to check the number of processors detected, use the nodes info API with the os flag.

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