41 lines
2.0 KiB
Markdown
41 lines
2.0 KiB
Markdown
# Detecting Slow Consumers
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In this section we will discuss how Apache ActiveMQ Artemis can be configured to deal
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with slow consumers. A slow consumer with a server-side queue (e.g. JMS
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topic subscriber) can pose a significant problem for broker performance.
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If messages build up in the consumer's server-side queue then memory
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will begin filling up and the broker may enter paging mode which would
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impact performance negatively. However, criteria can be set so that
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consumers which don't acknowledge messages quickly enough can
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potentially be disconnected from the broker which in the case of a
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non-durable JMS subscriber would allow the broker to remove the
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subscription and all of its messages freeing up valuable server
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resources.
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## Configuration required for detecting slow consumers
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By default the server will not detect slow consumers. If slow consumer
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detection is desired then see [address model chapter](address-model.md)
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for more details on the required address settings.
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The calculation to determine whether or not a consumer is slow only
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inspects the number of messages a particular consumer has
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*acknowledged*. It doesn't take into account whether or not flow control
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has been enabled on the consumer, whether or not the consumer is
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streaming a large message, etc. Keep this in mind when configuring slow
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consumer detection.
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Please note that slow consumer checks are performed using the scheduled
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thread pool and that each queue on the broker with slow consumer
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detection enabled will cause a new entry in the internal
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`java.util.concurrent.ScheduledThreadPoolExecutor` instance. If there
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are a high number of queues and the `slow-consumer-check-period` is
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relatively low then there may be delays in executing some of the checks.
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However, this will not impact the accuracy of the calculations used by
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the detection algorithm. See [thread pooling](thread-pooling.md) for more details about this pool.
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## Example
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See the [examples](examples.md) chapter for an example which shows how to detect a slow consumer
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with Apache ActiveMQ Artemis.
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