53 lines
3.8 KiB
XML
53 lines
3.8 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!-- ============================================================================= -->
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<!-- Licensed to the Apache Software Foundation (ASF) under one or more -->
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<!-- contributor license agreements. See the NOTICE file distributed with -->
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<!-- this work for additional information regarding copyright ownership. -->
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<!-- The ASF licenses this file to You under the Apache License, Version 2.0 -->
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<!-- (the "License"); you may not use this file except in compliance with -->
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<!-- the License. You may obtain a copy of the License at -->
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<!-- -->
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<!-- http://www.apache.org/licenses/LICENSE-2.0 -->
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<!-- -->
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<!-- Unless required by applicable law or agreed to in writing, software -->
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<!-- distributed under the License is distributed on an "AS IS" BASIS, -->
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<!-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. -->
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<!-- See the License for the specific language governing permissions and -->
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<!-- limitations under the License. -->
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<!-- ============================================================================= -->
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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % BOOK_ENTITIES SYSTEM "ActiveMQ_User_Manual.ent">
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%BOOK_ENTITIES;
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]>
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<chapter id="slow-consumers">
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<title>Detecting Slow Consumers</title>
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<para>In this section we will discuss how ActiveMQ can be configured to deal with slow consumers. A slow consumer with
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a server-side queue (e.g. JMS topic subscriber) can pose a significant problem for broker performance. If messages
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build up in the consumer's server-side queue then memory will begin filling up and the broker may enter paging
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mode which would impact performance negatively. However, criteria can be set so that consumers which don't
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acknowledge messages quickly enough can 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 subscription and all of its messages freeing up
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valuable server resources.
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</para>
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<section id="slow.consumer.configuration">
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<title>Configuration required for detecting slow consumers</title>
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<para>By default the server will not detect slow consumers. If slow consumer detection is desired then see
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<xref linkend="queue-attributes.address-settings"/>
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for more details.
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</para>
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<para>The calculation to determine whether or not a consumer is slow only inspects the number of messages a
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particular consumer has <emphasis>acknowledged</emphasis>. It doesn't take into account whether or not flow
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control has been enabled on the consumer, whether or not the consumer is streaming a large message, etc. Keep
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this in mind when configuring slow consumer detection.
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</para>
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<para>Please note that slow consumer checks are performed using the scheduled thread pool and that each queue on
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the broker with slow consumer detection enabled will cause a new entry in the internal
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<literal>java.util.concurrent.ScheduledThreadPoolExecutor</literal> instance. If there are a high number of
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queues and the <literal>slow-consumer-check-period</literal> is relatively low then there may be delays in
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executing some of the checks. However, this will not impact the accuracy of the calculations used by the
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detection algorithm. See <xref linkend="server.scheduled.thread.pool"/> for more details about this pool.
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</para>
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</section>
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</chapter>
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