[[modules-threadpool]]
== Thread Pool

A node holds several thread pools in order to improve how threads are
managed and memory consumption within a node. There are several thread
pools, but the important ones include:

[horizontal]
`index`:: 
    For index/delete operations, defaults to `fixed`, 
    size `# of available processors`. 
    queue_size `200`.

`search`:: 
    For count/search operations, defaults to `fixed`,
    size `3x # of available processors`. 
    queue_size `1000`.

`suggest`::
    For suggest operations, defaults to `fixed`,
    size `# of available processors`.
    queue_size `1000`.

`get`:: 
    For get operations, defaults to `fixed`
    size `# of available processors`.
    queue_size `1000`.

`bulk`::
    For bulk operations, defaults to `fixed`
    size `# of available processors`.
    queue_size `50`.

`percolate`::
    For percolate operations, defaults to `fixed`
    size `# of available processors`.
    queue_size `1000`.

`snapshot`::
    For snapshot/restore operations, defaults to `scaling`
    keep-alive `5m`,
    size `(# of available processors)/2`.

`snapshot_data`::
    For snapshot/restore operations on data files, defaults to `scaling`
    with a `5m` keep-alive,
    size `5`.

`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.

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:

[source,js]
--------------------------------------------------
threadpool:
    index:
        type: fixed
        size: 30
--------------------------------------------------

NOTE: you can update threadpool settings live using
      <<cluster-update-settings>>.


[float]
[[types]]
=== Thread pool types

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

[float]
==== `cache`

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:

[source,js]
--------------------------------------------------
threadpool:
    index:
        type: cached
--------------------------------------------------

[float]
==== `fixed`

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.

[source,js]
--------------------------------------------------
threadpool:
    index:
        type: fixed
        size: 30
        queue_size: 1000
--------------------------------------------------

[float]
[[processors]]
=== Processors setting
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.