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diff --git a/doc/book/src/java-broker/How-to-Use-SlowConsumerDisconnect.xml b/doc/book/src/java-broker/How-to-Use-SlowConsumerDisconnect.xml deleted file mode 100644 index 4e0ce0f7e0..0000000000 --- a/doc/book/src/java-broker/How-to-Use-SlowConsumerDisconnect.xml +++ /dev/null @@ -1,280 +0,0 @@ -<?xml version="1.0" encoding="utf-8"?> -<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" - "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"> -<!-- - - Licensed to the Apache Software Foundation (ASF) under one - or more contributor license agreements. See the NOTICE file - distributed with this work for additional information - regarding copyright ownership. The ASF licenses this file - to you under the Apache License, Version 2.0 (the - "License"); you may not use this file except in compliance - with the License. You may obtain a copy of the License at - - http://www.apache.org/licenses/LICENSE-2.0 - - Unless required by applicable law or agreed to in writing, - software distributed under the License is distributed on an - "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY - KIND, either express or implied. See the License for the - specific language governing permissions and limitations - under the License. - ---> -<section id="Java-Broker-Slow-Consumer-Disconnect"> - <title>Slow Consumer Disconnect - User Guide</title> - - <section> -<title>Introduction</title> - <para>Slow Consumer Disconnect (SCD) is a new feature in Qpid that provides a configurable - mechanism to prevent a single slow consumer from causing a back up of unconsumed messages on - the broker. </para> - - <para>This is most relevant where Topics are in use, since a published message is not removed - from the broker's memory until all subscribers have acknowledged that message. </para> - - <para>Cases where a consumer is 'slow' can arise due to one of the following: poor network - connectivity exists; a transient system issue affects a single client; a single subscriber - written by a client team is behaving incorrectly and not acknowledging messages; a - downstream resource such as a database is non-responsive. </para> - - <para>SCD will enable the application owner to configure limits for a given consumer's queue and - the behaviour to execute when those limits are reached. </para> - - </section> - - <section> -<title>What can it do?</title> - <para>SCD is only applicable to topics or durable subscriptions and can be configured on either - a topic or a subscription name. </para> - - <para>On triggering of a specified threshold the offending client will be disconnected from the - broker with a 506 error code wrapped in a JMSException returned to the client via the - ExceptionListener registered on the Connection object. </para> - - <para>Note that it is essential that an ExceptionListener be specified by the client on - creation of the connection and that exceptions coming back on that listener are handled - correctly. </para> - - </section> - - <section> -<title>Frequency of SCD Checking</title> - <section> -<title><emphasis role='bold'>Configuring Frequency</emphasis></title> - <para>You can configure the frequency with which the SCD process will check for slow consumers, - along with the unit of time used to specify that frequency. </para> - - <para>The <emphasis role="italic">virtualhosts.virtualhost.hostname.slow-consumer-detection</emphasis> - elements <emphasis role="italic">delay</emphasis> and <emphasis role="italic">timeunit</emphasis> - are used to specify the frequency and timeunit respectively in the virtualhosts.xml - file e.g. </para> - -<programlisting> -<virtualhosts> - <default>test</default> - <virtualhost> - <name>test</name> - <test> - <slow-consumer-detection> - <delay>60<delay/> - <timeunit>seconds<timeunit/> - <slow-consumer-detection/> - </test> - </virtualhost> -</virtualhosts> -</programlisting> - - </section> - - <section> -<title><emphasis role='bold'>SCD Log output</emphasis></title> - <para>When the SCD component finds a queue with a configured threshold to check, the operational - logging component (if enabled) will output the following line:</para> - - <programlisting> - SCD-1003 : Checking Status of Queue - </programlisting> - - </section> - - </section> - - <section> -<title>Client Exception<emphasis role='bold'>s</emphasis></title> - <para>When a Slow Consumer is disconnected, the client receives a 506 error from the broker - wrapped in a JMSException and the Session and Connection are closed:</para> - -<programlisting> -Dispatcher-Channel-1 2010-09-01 16:23:34,206 INFO [qpid.client.AMQSession.Dispatcher] - Dispatcher-Channel-1 thread terminating for channel 1:org.apache.qpid.client.AMQSession_0_8@1de8aa8 -pool-2-thread-3 2010-09-01 16:23:34,238 INFO [apache.qpid.client.AMQConnection] Closing AMQConnection due to - :org.apache.qpid.AMQChannelClosedException: Error: Consuming to slow. [error code 506: resource error] -javax.jms.JMSException: 506 -at org.apache.qpid.client.AMQConnection.exceptionReceived(AMQConnection.java:1396) -at org.apache.qpid.client.protocol.AMQProtocolHandler.exception(AMQProtocolHandler.java:329) -at org.apache.qpid.client.protocol.AMQProtocolHandler.methodBodyReceived(AMQProtocolHandler.java:536) -at org.apache.qpid.client.protocol.AMQProtocolSession.methodFrameReceived(AMQProtocolSession.java:453) -at org.apache.qpid.framing.AMQMethodBodyImpl.handle(AMQMethodBodyImpl.java:93) -at org.apache.qpid.client.protocol.AMQProtocolHandler$1.run(AMQProtocolHandler.java:462) -at org.apache.qpid.pool.Job.processAll(Job.java:110) -at org.apache.qpid.pool.Job.run(Job.java:149) -at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885) -at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907) -at java.lang.Thread.run(Thread.java:619) -Caused by: org.apache.qpid.AMQChannelClosedException: Error: Consuming to slow. [error code 506: resource error] -at org.apache.qpid.client.handler.ChannelCloseMethodHandler.methodReceived(ChannelCloseMethodHandler.java:96) -at org.apache.qpid.client.handler.ClientMethodDispatcherImpl.dispatchChannelClose(ClientMethodDispatcherImpl.java:163) -at org.apache.qpid.framing.amqp_8_0.ChannelCloseBodyImpl.execute(ChannelCloseBodyImpl.java:140) -at org.apache.qpid.client.state.AMQStateManager.methodReceived(AMQStateManager.java:112) -at org.apache.qpid.client.protocol.AMQProtocolHandler.methodBodyReceived(AMQProtocolHandler.java:511) -... 8 more -main 2010-09-01 16:23:34,316 INFO [apache.qpid.client.AMQSession] Closing session: - org.apache.qpid.client.AMQSession_0_8@ffeef1 -</programlisting> - - </section> - - <section> -<title>Disconnection Thresholds</title> - <section> -<title>Topic Subscriptions</title> - <para>One key feature of SCD is the disconnection of a consuming client when a specified - threshold is exceeded. For a pub-sub model using topics, this means that messages will no - longer be delivered to the private queue which was associated with that consuming client, - thus reducing any associated backlog in the broker. </para> - - </section> - - <section> -<title>Durable Topic Subscriptions</title> - <para>For durable subscriptions, simply disconnecting the consuming client will not suffice - since the associated queue is by definition durable and messages would continue to flow to - it after disconnection, potentially worsening any backing up of data on the broker. </para> - - <para>The solution is to configure durable subscriptions to delete the underlying queue on - disconnection. This means that messages will no longer be delivered to the private queue - associated with the subscription, thus preventing any backlog. </para> - - <para>Full details of how to configure the thresholds are provided below. </para> - - </section> - - <section> -<title>Message Age Threshold</title> - <para>You can configure SCD to be triggered on a topic or subscription when the oldest message - in the associated private queue for the consumer ages beyond the specified value, in - milliseconds. </para> - - </section> - - <section> -<title>Queue Depth Threshold</title> - <para>You can opt to use the depth of the queue in bytes as a threshold. SCD will be triggered - by a queue depth greater than the threshold specified i.e. when a broker receives a - message that takes the queue depth over the threshold. </para> - - </section> - - <section> -<title>Message Count Threshold</title> - <para>You can use the message count for the consumer's queue as the trigger, where a count - higher than that specified will trigger disconnection. </para> - - </section> - - <section> -<title><emphasis role='bold'>Delete Policy</emphasis></title> - <para>You can configure the policy you wish to apply in your broker configuration. There are - currently 2 policies available: </para> - - <para> -<emphasis role='bold'>Delete Temporary Queues Only</emphasis> - </para> - - <para>If you do not specify a <topicDelete/> element in your configuration, then only temporary - queues associated with a topic subscription will be deleted on client disconnect. This is - the default behaviour. </para> - <para/> - - <para> -<emphasis role='bold'>Delete Durable Subscription Queues</emphasis> - </para> - - <para>If you add the <topicDelete/> element with the sub-element - <delete-persistent/> to your config, then the persistent queue which is associated - with durable subscriptions to a topic will also be deleted. This is an important - consideration since without deleting the underlying queue the client's unconsumed data - will grow indefinitely while they will be unable to reconnect to that queue due to the SCD - threshold configured, potentially having an adverse effect on the application or broker in - use.</para> - <para/> - - <para><emphasis role="bold"> Example Topic Configuration </emphasis></para> - - <para/> - - <para> -The following steps are required to configure SCD: - </para> - -<itemizedlist> - <listitem> - <para>Enable SCD checking for your virtual host</para> - </listitem> - <listitem> - <para>Specify frequency for SCD checking</para> - </listitem> - <listitem> - <para>Define thresholds for the topic</para> - </listitem> - <listitem> - <para>Define the policy to apply on trigger </para> - </listitem> -</itemizedlist> - - <para>The example below shows a simple definition, with all three thresholds specified and a - simple disconnection, with deletion of any temporary queue, defined. </para> - - <para>For a durable subscription to this topic, no queue deletion would be applied on disconnect - - which is likely to be undesirable (see section above). </para> - -<programlisting> -<topics> - <topic> - <name>stocks.us.*</name> - <slow-consumer-detection> - <!-- The maximum depth before which --> - <!-- the policy will be applied--> - <depth>4235264</depth> - <!-- The maximum message age before which --> - <!-- the policy will be applied--> - <messageAge>600000</messageAge> - <!-- The maximum number of message before --> - <!-- which the policy will be applied--> - <messageCount>50</messageCount> - <!-- Policy Selection --> - <policy name="TopicDelete"/> - </slow-consumer-detection> - </topic> -</topics> -</programlisting> - - </section> - - </section> - - <section> -<title>Important Points To Note</title> - <para> Client application developers should be educated about how to correctly handle being - disconnected with a 506 error code, to avoid them getting into a thrashing state where they - continually attempt to connect, fail to consume fast enough and are disconnected again. </para> - - <para>Clients affected by slow consumer disconnect configuration should always use transactions - where duplicate processing of an incoming message would have adverse affects, since they may - receive a message more than once if disconnected before acknowledging a message in flight. </para> - - </section> - - </section> - |