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Thread Pool
editThread Pool
editA 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:
|
For index/delete operations. Defaults to |
|
For count/search operations. Defaults to |
|
For suggest operations. Defaults to |
|
For get operations. Defaults to |
|
For bulk operations. Defaults to |
|
For percolate operations. Defaults to |
|
For snapshot/restore operations. Defaults to |
|
For segment warm-up operations. Defaults to |
|
For refresh operations. Defaults to |
|
Mainly for java client executing of action when listener threaded is set to true.
Default size of |
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
editThe following are the types of thread pools that can be used and their respective parameters:
cache
editThe 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
editThe 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
editThe number of processors is automatically detected, and the thread pool
settings are automatically set based on it. In some cases it can be
useful to override the number of detected processors. This can be done
by explicitly setting the processors
setting.
processors: 4
There are a few use-cases for explicitly overriding the processors
setting:
-
If you are running multiple instances of Elasticsearch on the same
host but want Elasticsearch to size its thread pools as if it only has a
fraction of the CPU, you should override the
processors
setting to the desired fraction (e.g., if you’re running two instances of Elasticsearch on a 16-core machine, setprocessors
to 8). Note that this is an expert-level use-case and there’s a lot more involved than just setting theprocessors
setting as there are other considerations like changing the number of garbage collector threads, pinning processes to cores, etc. -
The number of processors is by default bounded to 32. This means that
on systems that have more than 32 processors, Elasticsearch will size
its thread pools as if there are only 32 processors present. This
limitation was added to avoid creating too many threads on systems that
have not properly adjusted the
ulimit
for max number of processes. In cases where you’ve adjusted theulimit
appropriately, you can override this bound by explicitly setting theprocessors
setting. -
Sometimes the number of processors is wrongly detected and in such
cases explicitly setting the
processors
setting will workaround such issues.
In order to check the number of processors detected, use the nodes info
API with the os
flag.