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#21209: Added docs for cpu-idle and large messages

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Endre Sándor Varga 2016-09-29 16:05:38 +02:00
parent a0f2120e8b
commit 4112206974
1 changed files with 46 additions and 4 deletions
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akka-docs/rst/scala/remoting-artery.rst
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@ -399,10 +399,39 @@ demonstrates both remote deployment and look-up of remote actors.
Performance tuning
------------------
Dedicated lane for large messages
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Dedicated subchannel for large messages
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TODO
All the communication between user defined remote actors are isolated from the channel of Akka internal messages so
a large user message cannot block an urgent system message. While this provides good isolation for Akka services, all
user communications by default happen through a shared network connection (an Aeron stream). When some actors
send large messages this can cause other messages to suffer higher latency as they need to wait until the full
message has been transported on the shared channel (and hence, shared bottleneck). In these cases it is usually
helpful to separate actors that have different QoS requirements: large messages vs. low latency.
Akka remoting provides a dedicated channel for large messages if configured. Since actor message ordering must
not be violated the channel is actually dedicated for *actors* instead of messages, to ensure all of the messages
arrive in send order. It is possible to assign actors on given paths to use this dedicated channel by using
path patterns:
akka.remote.artery.large-message-destinations = [
"/user/largeMessageActor",
"/user/largeMessagesGroup/*",
"/user/anotherGroup/*/largeMesssages",
"/user/thirdGroup/**",
]
This means that all messages sent to the following actors will pass through the dedicated, large messages channel:
* ``/user/largeMessageActor``
* ``/user/largeMessageActorGroup/actor1``
* ``/user/largeMessageActorGroup/actor2``
* ``/user/anotherGroup/actor1/largeMessages``
* ``/user/anotherGroup/actor2/largeMessages``
* ``/user/thirdGroup/actor3/``
* ``/user/thirdGroup/actor4/actor5``
Messages destined for actors not matching any of these patterns are sent using the default channel as before.
External, shared Aeron media driver
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@ -412,7 +441,20 @@ TODO
Fine-tuning CPU usage latency tradeoff
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TODO
Artery has been designed for low latency and as a result it can be CPU hungry when the system is mostly idle.
This is not always desirable. It is possible to tune the tradeoff between CPU usage and latency with
the following configuration:
# Values can be from 1 to 10, where 10 strongly prefers latency
# and 1 strongly prefers less CPU usage
akka.remote.artery.advanced.idle-cpu-level = 1
By setting this value to a lower number, it tells Akka to do longer "sleeping" periods on its thread dedicated
for `spin-waiting <https://en.wikipedia.org/wiki/Busy_waiting>`_ and hence reducing CPU load when there is no
immediate task to execute at the cost of a longer reaction time to an event when it actually happens. It is worth
to be noted though that during a continuously high-throughput period this setting makes not much difference
as the thread mostly has tasks to execute. This also means that under high throughput (but below maximum capacity)
the system might have less latency than at low message rates.
Remote Configuration
--------------------