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2fa6448a15
This commit introduces a new thread pool, `system_read`, which is intended for use by system indices for all read operations (get and search). The `system_read` pool is a fixed thread pool with a maximum number of threads equal to lesser of half of the available processors or 5. Given the combination of both get and read operations in this thread pool, the queue size has been set to 2000. The motivation for this change is to allow system read operations to be serviced in spite of the number of user searches. In order to avoid a significant performance hit due to pattern matching on all search requests, a new metadata flag is added to mark indices as system or non-system. Previously created system indices will have flag added to their metadata upon upgrade to a version with this capability. Additionally, this change also introduces a new class, `SystemIndices`, which encapsulates logic around system indices. Currently, the class provides a method to check if an index is a system index and a method to find a matching index descriptor given the name of an index. Relates #50251 Relates #37867 Backport of #57936
225 lines
8.1 KiB
Plaintext
225 lines
8.1 KiB
Plaintext
[[modules-threadpool]]
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=== Thread pools
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A node uses several thread pools to manage memory consumption.
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Queues associated with many of the thread pools enable pending requests
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to be held instead of discarded.
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There are several thread pools, but the important ones include:
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`generic`::
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For generic operations (for example, background node discovery).
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Thread pool type is `scaling`.
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[[search-threadpool]]
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`search`::
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For count/search/suggest operations. Thread pool type is
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`fixed_auto_queue_size` with a size of `int((`<<node.processors,
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`# of allocated processors`>>`pass:[ * ]3) / 2) + 1`, and initial queue_size of
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`1000`.
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[[search-throttled]]`search_throttled`::
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For count/search/suggest/get operations on `search_throttled indices`.
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Thread pool type is `fixed_auto_queue_size` with a size of `1`, and initial
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queue_size of `100`.
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`get`::
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For get operations. Thread pool type is `fixed`
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with a size of <<node.processors, `# of allocated processors`>>,
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queue_size of `1000`.
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`analyze`::
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For analyze requests. Thread pool type is `fixed` with a size of `1`, queue
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size of `16`.
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`write`::
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For single-document index/delete/update and bulk requests. Thread pool type
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is `fixed` with a size of <<node.processors, `# of allocated processors`>>,
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queue_size of `10000`. The maximum size for this pool is
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`pass:[1 + ]`<<node.processors, `# of allocated processors`>>.
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`snapshot`::
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For snapshot/restore operations. Thread pool type is `scaling` with a
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keep-alive of `5m` and a max of `min(5, (`<<node.processors,
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`# of allocated processors`>>`) / 2)`.
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`warmer`::
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For segment warm-up operations. Thread pool type is `scaling` with a
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keep-alive of `5m` and a max of `min(5, (`<<node.processors,
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`# of allocated processors`>>`) / 2)`.
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`refresh`::
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For refresh operations. Thread pool type is `scaling` with a
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keep-alive of `5m` and a max of `min(10, (`<<node.processors,
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`# of allocated processors`>>`) / 2)`.
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`listener`::
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Mainly for java client executing of action when listener threaded is set to
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`true`. Thread pool type is `scaling` with a default max of
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`min(10, (`<<node.processors, `# of allocated processors`>>`) / 2)`.
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`fetch_shard_started`::
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For listing shard states.
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Thread pool type is `scaling` with keep-alive of `5m` and a default maximum
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size of `pass:[2 * ]`<<node.processors, `# of allocated processors`>>.
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`fetch_shard_store`::
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For listing shard stores.
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Thread pool type is `scaling` with keep-alive of `5m` and a default maximum
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size of `pass:[2 * ]`<<node.processors, `# of allocated processors`>>.
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`flush`::
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For <<indices-flush,flush>>, <<indices-synced-flush-api,synced flush>>, and
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<<index-modules-translog, translog>> `fsync` operations. Thread pool type is
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`scaling` with a keep-alive of `5m` and a default maximum size of `min(5, (`
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<<node.processors, `# of allocated processors`>>`) / 2)`.
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`force_merge`::
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For <<indices-forcemerge,force merge>> operations.
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Thread pool type is `fixed` with a size of 1 and an unbounded queue size.
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`management`::
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For cluster management.
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Thread pool type is `scaling` with a keep-alive of `5m` and a default
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maximum size of `5`.
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`system_read`::
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For read operations on system indices.
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Thread pool type is `fixed` and a default maximum size of
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`min(5, (`<<node.processors, `# of allocated processors`>>`) / 2)`.
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Changing a specific thread pool can be done by setting its type-specific
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parameters; for example, changing the number of threads in the `write` thread
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pool:
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[source,yaml]
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--------------------------------------------------
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thread_pool:
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write:
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size: 30
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--------------------------------------------------
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[[thread-pool-types]]
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==== Thread pool types
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The following are the types of thread pools and their respective parameters:
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[[fixed-thread-pool]]
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===== `fixed`
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The `fixed` thread pool holds a fixed size of threads to handle the
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requests with a queue (optionally bounded) for pending requests that
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have no threads to service them.
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The `size` parameter controls the number of threads.
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The `queue_size` allows to control the size of the queue of pending
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requests that have no threads to execute them. By default, it is set to
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`-1` which means its unbounded. When a request comes in and the queue is
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full, it will abort the request.
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[source,yaml]
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--------------------------------------------------
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thread_pool:
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write:
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size: 30
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queue_size: 1000
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--------------------------------------------------
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[[fixed-auto-queue-size]]
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===== `fixed_auto_queue_size`
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experimental[]
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deprecated[7.7.0,The experimental `fixed_auto_queue_size` thread pool type is
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deprecated and will be removed in 8.0.]
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The `fixed_auto_queue_size` thread pool holds a fixed size of threads to handle
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the requests with a bounded queue for pending requests that have no threads to
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service them. It's similar to the `fixed` threadpool, however, the `queue_size`
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automatically adjusts according to calculations based on
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https://en.wikipedia.org/wiki/Little%27s_law[Little's Law]. These calculations
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will potentially adjust the `queue_size` up or down by 50 every time
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`auto_queue_frame_size` operations have been completed.
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The `size` parameter controls the number of threads.
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The `queue_size` allows to control the initial size of the queue of pending
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requests that have no threads to execute them.
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The `min_queue_size` setting controls the minimum amount the `queue_size` can be
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adjusted to.
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The `max_queue_size` setting controls the maximum amount the `queue_size` can be
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adjusted to.
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The `auto_queue_frame_size` setting controls the number of operations during
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which measurement is taken before the queue is adjusted. It should be large
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enough that a single operation cannot unduly bias the calculation.
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The `target_response_time` is a time value setting that indicates the targeted
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average response time for tasks in the thread pool queue. If tasks are routinely
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above this time, the thread pool queue will be adjusted down so that tasks are
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rejected.
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[source,yaml]
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--------------------------------------------------
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thread_pool:
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search:
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size: 30
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queue_size: 500
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min_queue_size: 10
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max_queue_size: 1000
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auto_queue_frame_size: 2000
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target_response_time: 1s
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--------------------------------------------------
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[[scaling-thread-pool]]
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===== `scaling`
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The `scaling` thread pool holds a dynamic number of threads. This
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number is proportional to the workload and varies between the value of
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the `core` and `max` parameters.
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The `keep_alive` parameter determines how long a thread should be kept
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around in the thread pool without it doing any work.
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[source,yaml]
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--------------------------------------------------
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thread_pool:
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warmer:
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core: 1
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max: 8
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keep_alive: 2m
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--------------------------------------------------
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[[node.processors]]
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==== Allocated processors setting
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The number of processors is automatically detected, and the thread pool settings
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are automatically set based on it. In some cases it can be useful to override
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the number of detected processors. This can be done by explicitly setting the
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`node.processors` setting.
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[source,yaml]
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--------------------------------------------------
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node.processors: 2
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--------------------------------------------------
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There are a few use-cases for explicitly overriding the `node.processors`
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setting:
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. If you are running multiple instances of {es} on the same host but want want
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{es} to size its thread pools as if it only has a fraction of the CPU, you
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should override the `node.processors` setting to the desired fraction, for
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example, if you're running two instances of {es} on a 16-core machine, set
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`node.processors` to 8. Note that this is an expert-level use case and there's
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a lot more involved than just setting the `node.processors` setting as there are
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other considerations like changing the number of garbage collector threads,
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pinning processes to cores, and so on.
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. Sometimes the number of processors is wrongly detected and in such cases
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explicitly setting the `node.processors` setting will workaround such issues.
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In order to check the number of processors detected, use the nodes info
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API with the `os` flag.
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