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ActiveMQ的消息重發(fā)策略和DLQ處理 博客分類： MQ

在以下三種情況中，ActiveMQ消息會(huì)被重發(fā)給客戶端/消費(fèi)者：?
1.使用一個(gè)事務(wù)session，并且調(diào)用了rollback()方法；?
2.一個(gè)事務(wù)session，關(guān)閉之前調(diào)用了commit；?
3.在session中使用CLIENT_ACKNOWLEDGE簽收模式，并且調(diào)用了Session.recover()方法。?

Broker根據(jù)自己的規(guī)則，通過BrokerInfo命令包和客戶端建立連接，向客戶端傳送缺省發(fā)送策略。但是客戶端可以使用ActiveMQConnection.getRedeliveryPolicy()方法覆蓋override這個(gè)策略設(shè)置。?

Java代碼

RedeliveryPolicy?policy?=?connection.getRedeliveryPolicy();??

policy.setInitialRedeliveryDelay(500);??

policy.setBackOffMultiplier(2);??

policy.setUseExponentialBackOff(true);??

policy.setMaximumRedeliveries(2);??

一旦消息重發(fā)嘗試超過重發(fā)策略中配置的maximumRedeliveries(缺省為6次)時(shí)，會(huì)給broker發(fā)送一個(gè)"Poison ack"，通知它，這個(gè)消息被認(rèn)為是一個(gè)毒丸(a poison pill)，接著broker會(huì)將這個(gè)消息發(fā)送到DLQ(Dead Letter Queue)，以便后續(xù)分析處理。?

缺省死信隊(duì)列(Dead Letter Queue)叫做ActiveMQ.DLQ;所有的未送達(dá)消息都會(huì)被發(fā)送到這個(gè)隊(duì)列，以致會(huì)非常難于管理。你可以設(shè)置activemq.xml文件中的destination policy map的"individualDeadLetterStrategy"屬性來修改.?

Java代碼

<broker...>??

??<destinationPolicy>??

????<policyMap>??

??????<policyEntries>??

????????<!--?Set?the?following?policy?on?all?queues?using?the?'>'?wildcard?-->??

????????<policyEntry?queue=">">??

??????????<deadLetterStrategy>??

????????????<!--??

??????????????Use?the?prefix?'DLQ.'?for?the?destination?name,?and?make??

??????????????the?DLQ?a?queue?rather?than?a?topic??

????????????-->??

????????????<individualDeadLetterStrategy??

??????????????queuePrefix="DLQ."?useQueueForQueueMessages="true"?/>??

??????????</deadLetterStrategy>??

????????</policyEntry>??

??????</policyEntries>??

????</policyMap>??

??</destinationPolicy>??

??...??

</broker>??

自動(dòng)丟棄過期消息(Expired Messages)?
一些應(yīng)用可能只是簡(jiǎn)單的丟棄過期消息，而不想將它們放到DLQ中，完全跳過了DLQ。在dead letter strategy死信策略上配置processExpired屬性為false，可以實(shí)現(xiàn)這個(gè)功能。?

Java代碼

<broker...>??

??<destinationPolicy>??

???<policyMap>??

?????<policyEntries>??

???????<!--?Set?the?following?policy?on?all?queues?using?the?'>'?wildcard?-->??

???????<policyEntry?queue=">">??

?????????<!--??

???????????Tell?the?dead?letter?strategy?not?to?process?expired?messages??

???????????so?that?they?will?just?be?discarded?instead?of?being?sent?to??

???????????the?DLQ??

?????????-->??

?????????<deadLetterStrategy>??

???????????<sharedDeadLetterStrategy?processExpired="false"?/>??

?????????</deadLetterStrategy>??

???????</policyEntry>??

?????</policyEntries>??

???</policyMap>??

??</destinationPolicy>??

...??

</broker>??

將非持久消息(non-persistent messages)放入死信隊(duì)列?
ActiveMQ缺省不會(huì)將未發(fā)到的非持久消息放入死信隊(duì)列。如果一個(gè)應(yīng)用程序并不想將消息message設(shè)置為持久的，那么記錄下來那些未發(fā)送到的消息對(duì)它來說往往也是沒有價(jià)值的。不過如果想實(shí)現(xiàn)這個(gè)功能，可以在dead-letter strategy死信策略上設(shè)置processNonPersistent="true"?

Java代碼

<broker...>??

??<destinationPolicy>??

???<policyMap>??

?????<policyEntries>??

???????<!--?Set?the?following?policy?on?all?queues?using?the?'>'?wildcard?-->??

???????<policyEntry?queue=">">??

?????????<!--??

???????????Tell?the?dead?letter?strategy?to?also?place?non-persisted?messages??

???????????onto?the?dead-letter?queue?if?they?can't?be?delivered.??

?????????-->??

?????????<deadLetterStrategy>??

???????????<sharedDeadLetterStrategy?processNonPersistent="true"?/>??

?????????</deadLetterStrategy>??

???????</policyEntry>??

?????</policyEntries>??

???</policyMap>??

??</destinationPolicy>??

...??

</broker>??

http://sharong.iteye.com/blog/1987171

轉(zhuǎn)載于:https://my.oschina.net/xiaominmin/blog/1597342

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