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Posted to commits@qpid.apache.org by or...@apache.org on 2016/12/28 10:37:57 UTC
[37/51] [partial] qpid-site git commit: Update site for 6.1.1 release
of Qpid Java
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+
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+ <h3>Messaging APIs</h3>
+
+ <ul>
+ <li><a href="/proton/index.html">Qpid Proton</a></li>
+ <li><a href="/components/jms/index.html">Qpid JMS</a></li>
+ <li><a href="/components/messaging-api/index.html">Qpid Messaging API</a></li>
+ </ul>
+ </section>
+
+ <section>
+ <h3>Servers and tools</h3>
+
+ <ul>
+ <li><a href="/components/java-broker/index.html">Broker for Java</a></li>
+ <li><a href="/components/cpp-broker/index.html">C++ broker</a></li>
+ <li><a href="/components/dispatch-router/index.html">Dispatch router</a></li>
+ </ul>
+ </section>
+
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+ <h3>Resources</h3>
+
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+ <li><a href="/dashboard.html">Dashboard</a></li>
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+ <ul id="-path-navigation"><li><a href="/index.html">Home</a></li><li><a href="/releases/index.html">Releases</a></li><li><a href="/releases/qpid-java-6.1.1/index.html">Qpid for Java 6.1.1</a></li><li><a href="/releases/qpid-java-6.1.1/java-broker/book/index.html">Apache Qpid Broker for Java</a></li><li>9.4. Handing Undeliverable Messages</li></ul>
+
+ <div id="-middle-content">
+ <div class="docbook"><div class="navheader"><table summary="Navigation header" width="100%"><tr><th align="center" colspan="3">9.4. Handing Undeliverable Messages</th></tr><tr><td align="left" width="20%"><a accesskey="p" href="Java-Broker-Runtime-Producer-Transaction-Timeout.html">Prev</a> </td><th align="center" width="60%">Chapter 9. Runtime</th><td align="right" width="20%"> <a accesskey="n" href="Java-Broker-Runtime-Close-Connection-When-No-Route.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="Java-Broker-Runtime-Handling-Undeliverable-Messages"></a>9.4. Handing Undeliverable Messages</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Runtime-Handling-Undeliverable-Messages-Introduction"></a>9.4.1. Introduction</h3></div></div></div><p> Messages that cannot be delivered successfu
lly to a consumer (for instance, because the
+ client is using a transacted session and rolls-back the transaction) can be made available on
+ the queue again and then subsequently be redelivered, depending on the precise session
+ acknowledgement mode and messaging model used by the application. This is normally desirable
+ behaviour that contributes to the ability of a system to withstand unexpected errors. However, it
+ leaves open the possibility for a message to be repeatedly redelivered (potentially indefinitely),
+ consuming system resources and preventing the delivery of other messages. Such undeliverable
+ messages are sometimes known as poison messages.</p><p>For an example, consider a stock ticker application that has been designed to consume prices
+ contained within JMS TextMessages. What if inadvertently a BytesMessage is placed onto the queue?
+ As the ticker application does not expect the BytesMessage, its processing might fail and cause it
+ to roll-back the transaction, however the default behavior of the Broker would mean that the
+ BytesMessage would be delivered over and over again, preventing the delivery of other legitimate
+ messages, until an operator intervenes and removes the erroneous message from the queue. </p><p>Qpid has maximum delivery count and dead-letter queue (DLQ) features which can be used in
+ concert to construct a system that automatically handles such a condition. These features are
+ described in the following sections.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Runtime-Handling-Undeliverable-Messages-Maximum-Delivery-Count"></a>9.4.2. Maximum Delivery Count</h3></div></div></div><p> Maximum delivery count is a property of a queue. If a consumer application is unable to
+ process a message more than the specified number of times, then the broker will either route the
+ message to a dead-letter queue (if one has been defined), or will discard the message. </p><p> In order for a maximum delivery count to be enforced, the consuming client
+ <span class="emphasis"><em>must</em></span> call <a class="link" href="http://docs.oracle.com/javaee/6/api/javax/jms/Session.html#rollback()" target="_top">Session#rollback()</a> (or <a class="link" href="http://docs.oracle.com/javaee/6/api/javax/jms/Session.html#recover()" target="_top">Session#recover()</a> if the session is not transacted). It is during the Broker's
+ processing of Session#rollback() (or Session#recover()) that if a message has been seen
+ at least the maximum number of times then it will move the message to the DLQ or discard the
+ message.</p><p>If the consuming client fails in another manner, for instance, closes the connection, the
+ message will not be re-routed and consumer application will see the same poison message again
+ once it reconnects.</p><p> If the consuming application is using AMQP 0-9-1, 0-9, or 0-8 protocols, it is necessary to
+ set the client system property <code class="varname">qpid.reject.behaviour</code> or connection or binding
+ URL option <code class="varname">rejectbehaviour</code> to the value <code class="literal">server</code>.</p><p>It is possible to determine the number of times a message has been sent to a consumer via
+ the Management interfaces, but is not possible to determine this information from a message client.
+ Specifically, the optional JMS message header <span class="property">JMSXDeliveryCount</span> is not
+ supported.</p><p>Maximum Delivery Count can be specified when a new queue is created or using the the
+ queue declare property <span class="property">x-qpid-maximum-delivery-count</span></p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Runtime-Handling-Undeliverable-Messages-Dead-Letter-Queues"></a>9.4.3. Dead Letter Queues (DLQ)</h3></div></div></div><p>A Dead Letter Queue (DLQ) acts as an destination for messages that have somehow exceeded the
+ normal bounds of processing and is utilised to prevent disruption to flow of other messages. When
+ a DLQ is enabled for a given queue if a consuming client indicates it no longer wishes the
+ receive the message (typically by exceeding a Maximum Delivery Count) then the message is moved
+ onto the DLQ and removed from the original queue. </p><p>The DLQ feature causes generation of a Dead Letter Exchange and a Dead Letter Queue. These
+ are named convention QueueName<span class="emphasis"><em>_DLE</em></span> and QueueName<span class="emphasis"><em>_DLQ</em></span>.</p><p>DLQs can be enabled when a new queue is created
+ or using the queue declare property <span class="property">x-qpid-dlq-enabled</span>.</p><div class="caution" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Avoid excessive queue depth</h3><p>Applications making use of DLQs <span class="emphasis"><em>should</em></span> make provision for the frequent
+ examination of messages arriving on DLQs so that both corrective actions can be taken to resolve
+ the underlying cause and organise for their timely removal from the DLQ. Messages on DLQs
+ consume system resources in the same manner as messages on normal queues so excessive queue
+ depths should not be permitted to develop.</p></div></div></div><div class="navfooter"><hr /><table summary="Navigation footer" width="100%"><tr><td align="left" width="40%"><a accesskey="p" href="Java-Broker-Runtime-Producer-Transaction-Timeout.html">Prev</a> </td><td align="center" width="20%"><a accesskey="u" href="Java-Broker-Runtime.html">Up</a></td><td align="right" width="40%"> <a accesskey="n" href="Java-Broker-Runtime-Close-Connection-When-No-Route.html">Next</a></td></tr><tr><td align="left" valign="top" width="40%">9.3. Producer Transaction Timeout </td><td align="center" width="20%"><a accesskey="h" href="AMQP-Messaging-Broker-Java-Book.html">Home</a></td><td align="right" valign="top" width="40%"> 9.5. Closing client connections on unroutable mandatory messages</td></tr></table></div></div>
+
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http://git-wip-us.apache.org/repos/asf/qpid-site/blob/6e5b75e1/content/releases/qpid-java-6.1.1/java-broker/book/Java-Broker-Runtime-Memory.html
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+<!DOCTYPE html>
+<!--
+ -
+ - Licensed to the Apache Software Foundation (ASF) under one
+ - or more contributor license agreements. See the NOTICE file
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+ - "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.
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+<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
+ <head>
+ <title>9.11. Memory - Apache Qpid™</title>
+ <meta http-equiv="X-UA-Compatible" content="IE=edge"/>
+ <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
+ <link rel="stylesheet" href="/site.css" type="text/css" async="async"/>
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+https://github.com/apache/qpid-proton/blob/go1{/dir}/{file}#L{line}"/>
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+ <li><a href="/components/index.html">Components</a></li>
+ <li><a href="/releases/index.html">Releases</a></li>
+ </ul>
+ </section>
+
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+ <h3>Messaging APIs</h3>
+
+ <ul>
+ <li><a href="/proton/index.html">Qpid Proton</a></li>
+ <li><a href="/components/jms/index.html">Qpid JMS</a></li>
+ <li><a href="/components/messaging-api/index.html">Qpid Messaging API</a></li>
+ </ul>
+ </section>
+
+ <section>
+ <h3>Servers and tools</h3>
+
+ <ul>
+ <li><a href="/components/java-broker/index.html">Broker for Java</a></li>
+ <li><a href="/components/cpp-broker/index.html">C++ broker</a></li>
+ <li><a href="/components/dispatch-router/index.html">Dispatch router</a></li>
+ </ul>
+ </section>
+
+ <section>
+ <h3>Resources</h3>
+
+ <ul>
+ <li><a href="/dashboard.html">Dashboard</a></li>
+ <li><a href="https://cwiki.apache.org/confluence/display/qpid/Index">Wiki</a></li>
+ <li><a href="/resources.html">More resources</a></li>
+ </ul>
+ </section>
+ </div>
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+
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+ <form action="http://www.google.com/search" method="get">
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+
+ <div id="-middle" class="panel">
+ <ul id="-path-navigation"><li><a href="/index.html">Home</a></li><li><a href="/releases/index.html">Releases</a></li><li><a href="/releases/qpid-java-6.1.1/index.html">Qpid for Java 6.1.1</a></li><li><a href="/releases/qpid-java-6.1.1/java-broker/book/index.html">Apache Qpid Broker for Java</a></li><li>9.11. Memory</li></ul>
+
+ <div id="-middle-content">
+ <div class="docbook"><div class="navheader"><table summary="Navigation header" width="100%"><tr><th align="center" colspan="3">9.11. Memory</th></tr><tr><td align="left" width="20%"><a accesskey="p" href="Java-Broker-Runtime-Connection-Limit.html">Prev</a> </td><th align="center" width="60%">Chapter 9. Runtime</th><td align="right" width="20%"> <a accesskey="n" href="Java-Broker-High-Availability.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="Java-Broker-Runtime-Memory"></a>9.11. Memory</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Runtime-Memory-Introduction"></a>9.11.1. Introduction</h3></div></div></div><p>
+ Understanding how the Qpid broker uses memory is essential to running a high performing and reliable service.
+ A wrongly configured broker can exhibit poor performance or even crash with an <code class="literal">OutOfMemoryError</code>.
+ Unfortunately, memory usage is not a simple topic and thus requires some in depth explanations.
+ This page should give the required background information to make informed decisions on how to configure your broker.
+ </p><p>
+ <a class="xref" href="Java-Broker-Runtime-Memory.html#Java-Broker-Runtime-Memory-Types" title="9.11.2. Types of Memory">Section 9.11.2, “Types of Memory”</a> explains the two different kinds of Java memory most relevant to the broker.
+ <a class="xref" href="Java-Broker-Runtime-Memory.html#Java-Broker-Runtime-Memory-Usage" title="9.11.3. Memory Usage in the Broker">Section 9.11.3, “Memory Usage in the Broker”</a> goes on to explain which parts of the broker use what kind of memory.
+ <a class="xref" href="Java-Broker-Runtime-Memory.html#Java-Broker-Runtime-Memory-Low-Memory" title="9.11.4. Low Memory Conditions">Section 9.11.4, “Low Memory Conditions”</a> explains what happens when the system runs low on memory.
+ <a class="xref" href="Java-Broker-Runtime-Memory.html#Java-Broker-Runtime-Memory-Defaults" title="9.11.5. Defaults">Section 9.11.5, “Defaults”</a> lays out the default settings of the Qpid broker.
+ Finally, <a class="xref" href="Java-Broker-Runtime-Memory.html#Java-Broker-Runtime-Memory-Tuning" title="9.11.6. Memory Tuning the Broker">Section 9.11.6, “Memory Tuning the Broker”</a> gives some advice on tuning your broker.
+ </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Runtime-Memory-Types"></a>9.11.2. Types of Memory</h3></div></div></div><p>
+ While Java has a couple of different internal memory types we will focus on the two types that are relevant to the Qpid broker.
+ Both of these memory types are taken from the same physical memory (RAM).
+ </p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="d0e6474"></a>9.11.2.1. Heap</h4></div></div></div><p>
+ Normally, all objects are allocated from Java's heap memory.
+ Once, nothing references an object it is cleaned up by the Java Garbage Collector and it's memory returned to the heap.
+ This works fine for most use cases.
+ However, when interacting with other parts of the operating system using Java's heap is not ideal.
+ This is where the so called direct memory comes into play.
+ </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="d0e6479"></a>9.11.2.2. Direct</h4></div></div></div><p>
+ The world outside of the JVM, in particular the operating system (OS), does not know about Java heap memory and uses other structures like C arrays.
+ In order to interact with these systems Java needs to copy data between its own heap memory and these native structures.
+ This can become a bottle neck when there is a lot of exchange between Java and the OS like in I/O (both disk and network) heavy applications.
+ Java's solution to this is to allow programmers to request <code class="literal">ByteBuffer</code>s from so called direct memory.
+ This is an opaque structure that <span class="emphasis"><em>might</em></span> have an underlying implementation that makes it efficient to interact with the OS.
+ Unfortunately, the GC is not good at tracking direct memory and in general it is inadvisable to use direct memory for regular objects.
+ </p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Runtime-Memory-Usage"></a>9.11.3. Memory Usage in the Broker</h3></div></div></div><p>
+ This section lists some note worthy users of memory within the broker and where possible lists their usage of heap and direct memory.
+ Note that to ensure smooth performance some heap memory should remain unused by the application and be reserved for the JVM to do house keeping and garbage collection.
+ <a class="link" href="https://docs.oracle.com/cd/E17277_02/html/java/com/sleepycat/je/util/DbCacheSize.html" target="_top">Some guides</a> advise to reserve up to 30% of heap memory for the JVM.
+ </p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="d0e6498"></a>9.11.3.1. Broker</h4></div></div></div><p>
+ The broker itself uses a moderate amount of heap memory (≈15 MB).
+ However, each connection and session comes with a heap overhead of about 17 kB and 15 kB respectively.
+ In addition, each connection reserves 512 kB direct memory for network I/O.
+ </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="d0e6503"></a>9.11.3.2. Virtual Hosts</h4></div></div></div><p>
+ The amount of memory a Virtual Host uses depends on its type.
+ For a JSON Virtual Host Node with a BDB Virtual Host the heap memory usage is approximately 2 MB.
+ However, each BDB Virtual Hosts has a mandatory cache in heap memory which has an impact on performance.
+ See <a class="link" href="Java-Broker-Runtime-Memory.html#Java-Broker-Runtime-Memory-Usage-BDB" title="9.11.3.4. Message Store">below</a> for more information.
+ </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="d0e6511"></a>9.11.3.3. Messages</h4></div></div></div><p>
+ Messages and their headers are kept in direct memory and have an additional overhead of approximately 1 kB heap memory each.
+ This means that most brokers will want to have more direct memory than heap memory.
+ When many small messages accumulate on the broker the 1 kB heap memory overhead can become a <a class="link" href="Java-Broker-Runtime-Memory.html#Java-Broker-Runtime-Memory-Low-Memory-Heap" title="9.11.4.1. Low on Heap Memory">limiting factor</a>.
+ </p><p>
+ When the broker is <a class="link" href="Java-Broker-Runtime-Memory.html#Java-Broker-Runtime-Memory-Low-Memory-Direct" title="9.11.4.2. Low on Direct Memory">running low on direct memory</a>
+ it will evict messages from memory and <a class="link" href="Java-Broker-Runtime-Flow-To-Disk.html" title="9.6. Flow to Disk">flow them to disk</a>.
+ For persistent messages this only means freeing the direct memory representation because they always have an on-disk representation to guard against unexpected failure (e.g., a power cut).
+ For transient messages this implies additional disk I/O.
+ After being flown to disk messages need to be re-read from disk before delivery.
+ </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="Java-Broker-Runtime-Memory-Usage-BDB"></a>9.11.3.4. Message Store</h4></div></div></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="d0e6530"></a>Berkeley DB (BDB)</h5></div></div></div><p>
+ The broker can use Oracle's BDB JE (BDB) as a message store to persist messages by writing them to a database.
+ BDB uses a mandatory cache for navigating and organising its database structure.
+ Sizing and tuning this cache is a topic of its own and would go beyond the scope of this guide.
+ Suffice to say that by default Qpid uses 5% of heap memory for BDB caches (each Virtual Host uses a separate cache) or 10 MB per BDB store, whichever is greater.
+ See the <a class="link" href="http://www.oracle.com/us/products/database/berkeley-db/je" target="_top">official webpage</a> especially <a class="link" href="http://docs.oracle.com/cd/E17277_02/html/java/com/sleepycat/je/util/DbCacheSize.html" target="_top">this page</a> for more information.
+ For those interested, Qpid uses <a class="link" href="http://docs.oracle.com/cd/E17277_02/html/java/com/sleepycat/je/CacheMode.html#EVICT_LN" target="_top">EVICT_LN</a> as its default JE cacheMode.
+ </p><p>
+ Note that due to licensing concerns Qpid does not ship the BDB JE jar files.
+ </p></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="d0e6546"></a>Derby</h5></div></div></div><p>
+ TODO
+ </p></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="d0e6551"></a>9.11.3.5. HTTP Management</h4></div></div></div><p>
+ Qpid uses Jetty for the HTTP Management (both REST and Web Management Console).
+ When the management plugin is loaded it will allocate the memory it needs and should not require more memory during operation and can thus be largely ignored.
+ </p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Runtime-Memory-Low-Memory"></a>9.11.4. Low Memory Conditions</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="Java-Broker-Runtime-Memory-Low-Memory-Heap"></a>9.11.4.1. Low on Heap Memory</h4></div></div></div><p>
+ When the broker runs low on heap memory performance will degrade because the JVM will trigger full garbage collection (GC) events in a struggle to free memory.
+ These full GC events are also called stop-the-world events as they completely halt the execution of the Java application.
+ Stop-the-world-events may take any where from a couple of milliseconds up to several minutes.
+ Should the heap memory demands rise even further the JVM will eventually throw an OutOfMemoryError which will cause the broker to shut down.
+ </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="Java-Broker-Runtime-Memory-Low-Memory-Direct"></a>9.11.4.2. Low on Direct Memory</h4></div></div></div><p>
+ When the broker detects that it uses 40% of available direct memory it will start flowing incoming transient messages to disk and reading them back before delivery.
+ This will prevent the broker from running out of direct memory but may degrade performance by requiring disk I/O.
+ </p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Runtime-Memory-Defaults"></a>9.11.5. Defaults</h3></div></div></div><p>
+ By default Qpid uses these settings:
+ </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ 0.5 GB heap memory
+ </li><li class="listitem">
+ 1.5 GB direct memory
+ </li><li class="listitem">
+ 5% of heap reserved for the JE cache.
+ </li><li class="listitem">
+ Start flow-to-disk at 40% direct memory utilisation.
+ </li></ul></div><p>
+ As an example, this would accommodate a broker with 50 connections, each serving 5 sessions, and each session having 1000 messages of 1 kB on queues in the broker.
+ This means a total of 250 concurrent sessions and a total of 250000 messages without flowing messages to disk.
+ </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Runtime-Memory-Tuning"></a>9.11.6. Memory Tuning the Broker</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="d0e6587"></a>9.11.6.1. Java Tuning</h4></div></div></div><p>
+ Most of these options are implementation specific. It is assumed you are using Oracle Java 1.7 and Qpid v6.
+ </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ Heap and direct memory can be configured through the <a class="link" href="Java-Broker-Appendix-Environment-Variables.html#Java-Broker-Appendix-Environment-Variables-Qpid-Java-Mem"><code class="literal">QPID_JAVA_MEM</code> environment variable</a>.
+ </li></ul></div><p>
+ </p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="d0e6601"></a>9.11.6.2. Qpid Tuning</h4></div></div></div><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ The system property <code class="literal">qpid.broker.bdbTotalCacheSize</code> sets the total amount of heap memory (in bytes) allocated to BDB caches.
+ </li><li class="listitem">
+ The system property <code class="literal">broker.flowToDiskThreshold</code> sets the threshold (in bytes) for flowing transient messages to disk.
+ Should the broker use more than direct memory it will flow incoming messages to disk.
+ Should utilisation fall beneath the threshold it will stop flowing messages to disk.
+ </li></ul></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="d0e6615"></a>9.11.6.3. Formulas</h4></div></div></div><p>
+ We developed a simple formula which estimates the <span class="emphasis"><em>minimum</em></span> memory usage of the broker under certain usage.
+ These are rough estimate so we strongly recommend testing your configuration extensively.
+ Also, if your machine has more memory available by all means use more memory as it can only improve the performance and stability of your broker.
+ However, remember that both heap and direct memory are served from your computer's physical memory so their sum should never exceed the physically available RAM (minus what other processes use).
+ </p><p>
+ </p><div class="informalequation"><span class="mathphrase">
+ memory<sub>heap</sub> = 15 MB + 15 kB * N<sub>sessions</sub> + 1.5 kB * N<sub>messages</sub> + 17 kB * N<sub>connections</sub>
+ </span></div><p>
+ </p><p>
+ </p><div class="informalequation"><span class="mathphrase">
+ memory<sub>direct</sub> = 2 MB + (200 B + averageSize<sub>msg</sub> *2)* N<sub>messages</sub> + 1MB * N<sub>connections</sub>
+ </span></div><p>
+ </p><p>
+ Where <span class="mathphrase">N</span> denotes the total number of connections/sessions/messages on the broker. Furthermore, for direct memory only the messages that have not been flown to disk are relevant.
+ </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The formulae assume the worst case in terms of memory usage: persistent messages and TLS connections. Transient messages consume less heap memory than peristent and plain connections consume less direct memory than TLS
+ connections.
+ </p></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="d0e6667"></a>9.11.6.4. Things to Consider</h4></div></div></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="d0e6670"></a>Performance</h5></div></div></div><p>
+ Choosing a smaller direct memory size will lower the threshold for flowing transient messages to disk when messages accumulate on a queue.
+ This can have impact on performance in the transient case where otherwise no disk I/O would be involved.
+ </p><p>
+ Having too little heap memory will result in poor performance due to frequent garbage collection events. See <a class="xref" href="Java-Broker-Runtime-Memory.html#Java-Broker-Runtime-Memory-Low-Memory" title="9.11.4. Low Memory Conditions">Section 9.11.4, “Low Memory Conditions”</a> for more details.
+ </p></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="d0e6679"></a>OutOfMemoryError</h5></div></div></div><p>
+ Choosing too low heap memory can cause an OutOfMemoryError which will force the broker to shut down.
+ In this sense the available heap memory puts a hard limit on the number of messages you can have in the broker at the same time.
+ </p><p>
+ If the Java runs out of direct memory it also throws a OutOfMemoryError resulting the a broker shutdown.
+ Under normal circumstances this should not happen but needs to be considered when deviating from the default configuration, especially when changing the flowToDiskThreshold.
+ </p><p>
+ If you are sending very large messages you should accommodate for this by making sure you have enough direct memory.
+ </p></div></div></div></div><div class="navfooter"><hr /><table summary="Navigation footer" width="100%"><tr><td align="left" width="40%"><a accesskey="p" href="Java-Broker-Runtime-Connection-Limit.html">Prev</a> </td><td align="center" width="20%"><a accesskey="u" href="Java-Broker-Runtime.html">Up</a></td><td align="right" width="40%"> <a accesskey="n" href="Java-Broker-High-Availability.html">Next</a></td></tr><tr><td align="left" valign="top" width="40%">9.10. Connection Limits </td><td align="center" width="20%"><a accesskey="h" href="AMQP-Messaging-Broker-Java-Book.html">Home</a></td><td align="right" valign="top" width="40%"> Chapter 10. High Availability</td></tr></table></div></div>
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+
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+ <div class="docbook"><div class="navheader"><table summary="Navigation header" width="100%"><tr><th align="center" colspan="3">9.9. Message Compression</th></tr><tr><td align="left" width="20%"><a accesskey="p" href="Java-Broker-Runtime-Background-Recovery.html">Prev</a> </td><th align="center" width="60%">Chapter 9. Runtime</th><td align="right" width="20%"> <a accesskey="n" href="Java-Broker-Runtime-Connection-Limit.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="Java-Broker-Runtime-Message-Compression"></a>9.9. Message Compression</h2></div></div></div><p>The Apache Qpid Broker for Java supports<a class="footnote" href="#ftn.d0e6382" id="d0e6382"><sup class="footnote">[13]</sup></a> message compression. This feature works in co-operation with Qpid
+ Clients implementing the same feature.</p><p>Once the feature is enabled (using Broker context variable
+ <span class="emphasis"><em>broker.messageCompressionEnabled</em></span>), the Broker will advertise support for the
+ message compression feature to the client at connection time. This allows clients to opt to turn
+ on message compression, allowing message payload sizes to be reduced.</p><p>If the Broker has connections from clients who have message compression enabled and others who
+ do not, it will internally, on-the-fly, decompress compressed messages when sending to clients
+ without support and conversely, compress uncomressed messages when sending to clients who do.</p><p>The Broker has a threshold below which it will not consider compressing a message, this is
+ controlled by Broker content variable
+ (<code class="literal">connection.messageCompressionThresholdSize</code>) and expresses a size in bytes.</p><p>This feature <span class="emphasis"><em>may</em></span> have a beneficial effect on performance by:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>Reducing the number of bytes transmitted over the wire, both between Client and Broker, and
+ in the HA case, Broker to Broker, for replication purposes.</p></li><li class="listitem"><p>Reducing storage space when data is at rest within the Broker, both on disk and in
+ memory.</p></li></ul></div><p>Of course, compression and decompression is computationally expensive. Turning on the feature
+ may have a negative impact on CPU utilization on Broker and/or Client. Also for small messages
+ payloads, message compression may increase the message size. It is recommended to test the feature
+ with representative data.</p><div class="footnotes"><br /><hr style="width:100; text-align:left;margin-left: 0" /><div class="footnote" id="ftn.d0e6382"><p><a class="para" href="#d0e6382"><sup class="para">[13] </sup></a>Message compression is not yet supported for the 1.0
+ protocol.</p></div></div></div><div class="navfooter"><hr /><table summary="Navigation footer" width="100%"><tr><td align="left" width="40%"><a accesskey="p" href="Java-Broker-Runtime-Background-Recovery.html">Prev</a> </td><td align="center" width="20%"><a accesskey="u" href="Java-Broker-Runtime.html">Up</a></td><td align="right" width="40%"> <a accesskey="n" href="Java-Broker-Runtime-Connection-Limit.html">Next</a></td></tr><tr><td align="left" valign="top" width="40%">9.8. Background Recovery </td><td align="center" width="20%"><a accesskey="h" href="AMQP-Messaging-Broker-Java-Book.html">Home</a></td><td align="right" valign="top" width="40%"> 9.10. Connection Limits</td></tr></table></div></div>
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+ <ul id="-path-navigation"><li><a href="/index.html">Home</a></li><li><a href="/releases/index.html">Releases</a></li><li><a href="/releases/qpid-java-6.1.1/index.html">Qpid for Java 6.1.1</a></li><li><a href="/releases/qpid-java-6.1.1/java-broker/book/index.html">Apache Qpid Broker for Java</a></li><li>9.3. Producer Transaction Timeout</li></ul>
+
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+ <div class="docbook"><div class="navheader"><table summary="Navigation header" width="100%"><tr><th align="center" colspan="3">9.3. Producer Transaction Timeout</th></tr><tr><td align="left" width="20%"><a accesskey="p" href="Java-Broker-Runtime-Disk-Space-Management.html">Prev</a> </td><th align="center" width="60%">Chapter 9. Runtime</th><td align="right" width="20%"> <a accesskey="n" href="Java-Broker-Runtime-Handling-Undeliverable-Messages.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="Java-Broker-Runtime-Producer-Transaction-Timeout"></a>9.3. Producer Transaction Timeout</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Runtime-Producer-Transaction-Timeout-GeneralInformation"></a>9.3.1. General Information</h3></div></div></div><p> The transaction timeout mechanism is used to c
ontrol broker resources when clients
+ producing messages using transactional sessions hang or otherwise become unresponsive, or simply
+ begin a transaction and keep using it without ever calling <a class="link" href="http://docs.oracle.com/javaee/6/api/javax/jms/Session.html#commit" target="_top">Session#commit()</a>.</p><p>Users can choose to configure an idleWarn or openWarn threshold, after which the identified
+ transaction should be logged as a WARN level alert as well as (more importantly) an idleClose or
+ openClose threshold after which the transaction and the connection it applies to will be
+ closed.</p><p>This feature is particularly useful in environments where the owner of the broker does not
+ have full control over the implementation of clients, such as in a shared services
+ deployment.</p><p>The following section provide more details on this feature and its use.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Runtime-Producer-Transaction-Timeout-Purpose"></a>9.3.2. Purpose</h3></div></div></div><p> This feature has been introduced to address the scenario where an open transaction on the
+ broker holds an open transaction on the persistent store. This can have undesirable consequences
+ if the store does not time out or close long-running transactions, such as with BDB. This can can
+ result in a rapid increase in disk usage size, bounded only by available space, due to growth of
+ the transaction log. </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Runtime-Producer-Transaction-Timeout-Scope"></a>9.3.3. Scope</h3></div></div></div><p>Note that only <a class="link" href="http://docs.oracle.com/javaee/6/api/javax/jms/MessageProducer.html" target="_top">MessageProducer</a> clients will be affected by a transaction timeout, since store
+ transaction lifespan on a consumer only spans the execution of the call to Session#commit() and
+ there is no scope for a long-lived transaction to arise.</p><p>It is also important to note that the transaction timeout mechanism is purely a JMS
+ transaction timeout, and unrelated to any other timeouts in the Qpid client library and will have
+ no impact on any RDBMS your application may utilise.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Runtime-Producer-Transaction-Timeout-Effect"></a>9.3.4. Effect</h3></div></div></div><p>Full details of configuration options are provided in the sections that follow. This section
+ gives a brief overview of what the Transaction Timeout feature can do.</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="Java-Broker-Runtime-Producer-Transaction-Timeout-Effect-Broker-Side"></a>9.3.4.1. Broker Logging and Connection Close</h4></div></div></div><p>When the openWarn or idleWarn specified threshold is exceeded, the broker will log a WARN
+ level alert with details of the connection and channel on which the threshold has been exceeded,
+ along with the age of the transaction.</p><p>When the openClose or idleClose specified threshold value is exceeded, the broker will
+ throw an exception back to the client connection via the <a class="link" href="http://docs.oracle.com/javaee/6/api/javax/jms/ExceptionListener.html" target="_top">ExceptionListener</a>, log the
+ action and then close the connection.</p><p>The example broker log output shown below is where the idleWarn threshold specified is
+ lower than the idleClose threshold and the broker therefore logs the idle transaction 3 times
+ before the close threshold is triggered and the connection closed out.</p><pre class="screen">CHN-1008 : Idle Transaction : 13,116 ms
+CHN-1008 : Idle Transaction : 14,116 ms
+CHN-1008 : Idle Transaction : 15,118 ms
+CHN-1003 : Close
+ </pre><p>The second example broker log output shown below illustrates the same mechanism operating
+ on an open transaction.</p><pre class="screen">
+CHN-1007 : Open Transaction : 12,406 ms
+CHN-1007 : Open Transaction : 13,406 ms
+CHN-1007 : Open Transaction : 14,406 ms
+CHN-1003 : Close
+ </pre></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="Java-Broker-Runtime-Producer-Transaction-Timeout-Effect-Client-Side"></a>9.3.4.2. Client Side Effect</h4></div></div></div><p>After a Close threshold has been exceeded, the trigger client will receive this exception
+ on its <a class="link" href="http://docs.oracle.com/javaee/6/api/javax/jms/ExceptionListener.html" target="_top">exception
+ listener</a>, prior to being disconnected:</p><code class="computeroutput">org.apache.qpid.AMQConnectionClosedException: Error: Idle transaction timed out
+ [error code 506: resource error]</code><p>Any later attempt to use the connection will result in this exception being thrown:</p><pre class="screen">Producer: Caught an Exception: javax.jms.IllegalStateException: Object org.apache.qpid.client.AMQSession_0_8@129b0e1 has been closed
+ javax.jms.IllegalStateException: Object org.apache.qpid.client.AMQSession_0_8@129b0e1 has been closed
+ at org.apache.qpid.client.Closeable.checkNotClosed(Closeable.java:70)
+ at org.apache.qpid.client.AMQSession.checkNotClosed(AMQSession.java:555)
+ at org.apache.qpid.client.AMQSession.createBytesMessage(AMQSession.java:573)
+ </pre><p>Thus clients must be able to handle this case successfully, reconnecting where required and
+ registering an exception listener on all connections. This is critical, and must be communicated
+ to client applications by any broker owner switching on transaction timeouts.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Runtime-Producer-Transaction-Timeout-Configuration"></a>9.3.5. Configuration</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="Java-Broker-Runtime-Producer-Transaction-Timeout-Configuration-Overview"></a>9.3.5.1. Configuration</h4></div></div></div><p>The transaction timeouts can be specified when a new virtualhost is created or an exiting
+ virtualhost is edited.</p><p>We would recommend that only warnings are configured at first, which should allow broker
+ administrators to obtain an idea of the distribution of transaction lengths on their systems,
+ and configure production settings appropriately for both warning and closure. Ideally
+ establishing thresholds should be achieved in a representative UAT environment, with clients and
+ broker running, prior to any production deployment.</p><p>It is impossible to give suggested values, due to the large variation in usage depending on
+ the applications using a broker. However, clearly transactions should not span the expected
+ lifetime of any client application as this would indicate a hung client.</p><p>When configuring warning and closure timeouts, it should be noted that these only apply to
+ message producers that are connected to the broker, but that a timeout will cause the connection
+ to be closed - this disconnecting all producers and consumers created on that connection.</p><p>This should not be an issue for environments using Mule or Spring, where connection
+ factories can be configured appropriately to manage a single MessageProducer object per JMS
+ Session and Connection. Clients that use the JMS API directly should be aware that sessions
+ managing both consumers and producers, or multiple producers, will be affected by a single
+ producer hanging or leaving a transaction idle or open, and closed, and must take appropriate
+ action to handle that scenario.</p></div></div></div><div class="navfooter"><hr /><table summary="Navigation footer" width="100%"><tr><td align="left" width="40%"><a accesskey="p" href="Java-Broker-Runtime-Disk-Space-Management.html">Prev</a> </td><td align="center" width="20%"><a accesskey="u" href="Java-Broker-Runtime.html">Up</a></td><td align="right" width="40%"> <a accesskey="n" href="Java-Broker-Runtime-Handling-Undeliverable-Messages.html">Next</a></td></tr><tr><td align="left" valign="top" width="40%">9.2. Disk Space Management </td><td align="center" width="20%"><a accesskey="h" href="AMQP-Messaging-Broker-Java-Book.html">Home</a></td><td align="right" valign="top" width="40%"> 9.4. Handing Undeliverable Messages</td></tr></table></div></div>
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