[rabbitmq-discuss] Published message not queued after publish-ok received when connection quickly closed

Fri Jul 8 15:28:40 BST 2011

Basic.Publish isn't pseudo-synchronous, it's really
asynchronous. Exchange#publish doesn't take nowait option (so no, your code
isn't safe), it simply send the data and that's it. Then you have no idea
whether everything went OK or not. That's why you can use either
transactions (yes, you'd have to wrap the code in it as you've mentioned) or
publisher confirms (which I'd personally prefer as transactions are really
slow and fairly tricky). The documentation for publisher confirms in AMQP
gem is here:
http://rdoc.info/github/ruby-amqp/amqp/master/file/docs/Durability.textile

Jakub

http://www.flickr.com/photos/jakub-stastny
http://twitter.com/botanicus

2011/7/8 Michael Nacos <m.nacos at gmail.com>

> so, what's currently the best way to publish messages consumed from one
> queue into another with the amqp gem? This is quite important in processing
> scenaria when no messages may be lost. In particular, is the following code
> safe? Will the pseudo-synchronous *publish* call return only after the
> message has been accepted in the second queue (:nowait => false)? otherwise,
> what would be the point of wrapping the publish call with @channel.tx_select
> / @channel.tx_commit ?
>
> # consumer which publishes each message to another queue
> # ------------------------------------------------------
>
> @consume_from = 'first'
> @deliver_to = 'second'
>
> EM.run do
>   AMQP.connect do |connection|
>     @channel = MQ.new(connection)
>     # making sure the relevant queues exist
>     @queue1 = @channel.queue(@consume_from, :passive => false, :durable =>
> true)
>     @queue2 = @channel.queue(@deliver_to, :passive => false, :durable =>
> true)
>     # setting up the consumer loop
>     @queue1.subscribe(:ack => true) do |metadata, data|
>       @channel.default_exchange.publish(data, \
>         :routing_key => @deliver_to, \
>         :persistent => true, \
>         :nowait => false)
>       puts '.'
>       metadata.ack
>     end
>   end
> end
>
>
> 2011/7/4 Jakub Šťastný <stastny at 101ideas.cz>
>
>> AMQP 0.8 is available as RC, it's way more stable than 0.7, so I would
>> recommend to just use the RC.
>>
>> Jakub
>>
>> http://www.flickr.com/photos/jakub-stastny
>> http://twitter.com/botanicus
>>
>>
>>
>> 2011/7/4 Michael Nacos <m.nacos at gmail.com>
>>
>>> there seems to be some support for tx_select, tx_commit, tx_rollback in
>>> the master branch of the amqp gem, but not in the 0.7.x-stable branch, which
>>> is what most people are using
>>>
>>> 2011/5/6 David Wragg <david at rabbitmq.com>
>>>
>>>> Simon MacMullen <simon at rabbitmq.com> writes:
>>>> > On 05/05/11 22:33, Elias Levy wrote:
>>>> >> While writing some code using the Ruby AMQP gem against RabbitMQ,
>>>> I've
>>>> >> noticed that if I publish a message and quickly close the connection,
>>>> >> even though I've received a publish-ok response from the server, the
>>>> >> message fails to be queued by the broker.
>>>> >
>>>> > I'm not at all familiar with the Ruby client, but I should point out
>>>> > that unlike many of the other AMQP methods, basic.publish does not
>>>> > have a corresponding basic.publish-ok method; it's always
>>>> > asynchronous. So I imagine the post-publish callback fires
>>>> > immediately.
>>>> >
>>>> > In order to be able to know when the broker has taken responsibility
>>>> > for a message you can either wrap the publish in a transaction (when
>>>> > you see tx.commit-ok you know the server has the message) or use the
>>>> > rather more lightweight publish confirms:
>>>> o>
>>>> >
>>>> http://www.rabbitmq.com/blog/2011/02/10/introducing-publisher-confirms/
>>>>
>>>> Another way to solve the problem is to do a synchronous AMQP method
>>>> rather than abruptly closing the connection.  If this the sync method
>>>> completes successfully, you can be sure that your published messages
>>>> have reached the broker (it doesn't give you all the guarantees of
>>>> transactions, but it is much lighter weight).
>>>>
>>>> An easy way to do this with all versions of the AMQP gem (even 0.6.7) is
>>>> to use the AMQP#close callback.  E.g., add something like this to your
>>>> code:
>>>>
>>>>  client.close { puts "Closed ok" ; EM.stop }
>>>>
>>>> David
>>>>
>>>> --
>>>> David Wragg
>>>> Staff Engineer, RabbitMQ
>>>> VMware, Inc.
>>>> _______________________________________________
>>>> rabbitmq-discuss mailing list
>>>> rabbitmq-discuss at lists.rabbitmq.com
>>>> https://lists.rabbitmq.com/cgi-bin/mailman/listinfo/rabbitmq-discuss
>>>>
>>>
>>>
>>
>
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