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Elastic Docs ›Elasticsearch Guide [1.5] ›Modules

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. The example below sets the number of processors to 4, which means that the default search thread pool size is 4 x 3 = 12.

processors: 4

This setting is important when running multiple node instances on a single bare-metal machine. Each node will detect that it has the full number of processors. But in reality, they are sharing processors on the single machine. In other words, it is advised to lower the processors setting accordingly. For example, on a 24 core machine and running 3 nodes, set processors to 8.

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

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