activemq-artemis/docs/user-manual/zh/pre-acknowledge.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<chapter id="pre-acknowledge">
<title>预先通知模式pre-acknowledge</title>
<para>JMS 规定了三种消息通知方式</para>
<itemizedlist>
<listitem>
<para><literal>AUTO_ACKNOWLEDGE</literal></para>
</listitem>
<listitem>
<para><literal>CLIENT_ACKNOWLEDGE</literal></para>
</listitem>
<listitem>
<para><literal>DUPS_OK_ACKNOWLEDGE</literal></para>
</listitem>
</itemizedlist>
<para>还有一种情况JMS不支持应用程序在出现故障时可以容忍消息丢失这样可以在消息在传递给客户
<emphasis>之前</emphasis>就通知服务器。</para>
<para>HornetQ支持这种模式称为<emphasis>pre-acknowledge</emphasis></para>
<para>这种模式的缺点是消息在通知后,如果系统出现故障时,消息可能丢失。并且在系统重启后该消息
不能恢复。</para>
<para>使用<literal>pre-acknowledgement</literal>模式可以节省网络传输和CPU处理资源。</para>
<para>股票价格更新是一个适用于此模式的例子。如果因为服务器故障丢失了一些消息,等服务器重启后新的
股票更新消息很快到达,以前丢失的过时的股票消息即使丢失也无关紧要。 </para>
<note>
<para>注意如果你使用pre-acknowledge模式在接收消息端不能支持事务。因为这个模式不是在提交时
通知消息,是在消息在传递之前就通知了。</para>
</note>
<section id="pre-acknowledge.configure">
<title>使用PRE_ACKNOWLEDGE</title>
<para>这个模式在<literal>hornetq-jms.xml</literal>文件中
<literal>connection factory</literal>下配置:</para>
<programlisting>&lt;connection-factory name="ConnectionFactory">
&lt;connectors>
&lt;connector-ref connector-name="netty-connector"/>
&lt;/connectors>
&lt;entries>
&lt;entry name="ConnectionFactory"/>
&lt;/entries>
&lt;pre-acknowledge>true&lt;/pre-acknowledge>
&lt;/connection-factory></programlisting>
<para>另一个选择是使用JMS接口来设置pre-acknowledgement模式。只需要在创建JMS会话session
时使用<literal>HornetQSession.PRE_ACKNOWLEDGE</literal>常数即可。</para>
<programlisting>
// messages will be acknowledge on the server *before* being delivered to the client
Session session = connection.createSession(false, HornetQSession.PRE_ACKNOWLEDGE);
</programlisting>
<para>你还可以直接在<literal>HornetQConnectionFactory</literal>实例上设置该模式。</para>
<para>另外,如果使用核心接口,则在<literal>ClientSessionFactory</literal>实例上直接
设置该模式。</para>
</section>
<section>
<title>例子</title>
<para>参见<xref linkend="examples.pre-acknowledge"/>。这是一个使用JMS的例子。</para>
</section>
</chapter>