[LRUG] AMQP threads. Where did my messages go?

Jim Myhrberg contact at jimeh.me
Fri Mar 21 05:30:27 PDT 2014


Hey Simon,

My AMQP skills have been gathering dust for a couple of years at this
point, but I'll see if I can help.

First, maybe I haven't had enough caffeine today, so would mind clarifying
if the issue is that the notification messages don't get pushed from the
Ruby worker, or they do show up fine in RabbitMQ and then disappear between
RabbitMQ and the Node.js worker?

If it's the former, one thing to keep in mind when using the amqp gem, is
that calling #push doesn't mean the message has been pushed, it means it
will be pushed at some point in the future when the event loop gets to it.
Typically if I recall, anything/everything pushed within processing one
AMQP message, get's all gets pushed at once after the ACK for the initial
message being processed is sent back to RabbitMQ. Another thing to keep in
mind is that killing the connection/process/whatever even after finishing
processing the initial message might cut off your messages being pushed.

The async nature of the amqp gem can cause some weird timing issues. Hence
when I last used AMQP we ended up replacing the amqp gem where async wasn't
specifically required with the synchronous bunny gem instead to make things
simpler.





--jimeh


On Fri, Mar 21, 2014 at 12:10 PM, Simon Morley <simon at polkaspots.com> wrote:

> Hi Tom, Steve
>
> Thanks for your emails.
>
> We have ack on for everything right now. We can see the 'parent' job being
> queued, the follow up jobs don't seem to be queued - I'll confirm this
> shortly.
>
> I have no unacked messages either right now.
>
> I'd thought the consumer might be dying which is why we ran the child job
> in a loop. No problems encountered.
>
> Just can't see why they work independently, just not as one.
>
> S
>
> Simon Morley
> Big Chief | PolkaSpots Supafly Wi-Fi
>
> simon at PolkaSpots.com
> 020 7183 1471
>
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> On 21 March 2014 11:59, Tom - Droplet <tom at dropletpay.com> wrote:
>
>> Hi Simon,
>>
>> What are your publisher confirm settings and consumer ack settings? Could
>> it be that the consumer dies during processing the job but you have
>> subscribed to the queue without requiring acks, so the message is
>> essentially lost?
>>
>> The RabbitMQ management page can be pretty useful for debugging this kind
>> of stuff sometimes, you can check that messages are getting put in the
>> queue as you expect and pull them out to see the message.
>>
>> --
>> Tom Livesey
>> Lead engineer - Droplet
>> dropletpay.com
>>
>>
>> On 21 March 2014 at 11:48:05, Simon Morley (simon at polkaspots.com) wrote:
>>
>> Morning All
>>
>> Having asked SO, I remembered we were supposed to be encouraging more
>> questions here! I hope you can help (sorry this is a long message).
>>
>> Relatively new to the world of RabbitMQ, I'm getting stuck debugging the
>> problem of missing messages. All was / is fine in my dev. environment, the
>> problems arise when we start chucking thousand of messages at things.
>>
>> I've narrowed the problem down to messages that are sent from within
>> another job. For example, we have a job that moves a customer's
>> subscription when they sign up. We publish this to our rabbit servers using
>> the AMQP gem and EM using something like this:
>>
>> https://gist.github.com/simonmorley/9684010
>>
>> def queue_process_subscription
>>    user. process_subscription
>> end
>>
>> def process_subscription
>>   hammer_time
>>   MESSAGE_QUEUE.push(json_message, 'ps.routing.key')
>> end
>>
>> After the job's been completed, we use MESSAGE_QUEUE to push a message to
>> our notification servers (which run NodeJS, node-amqp and SocketIO).
>>
>> On my lonely laptop, the jobs process perfectly, the notification are
>> sent and my SocketIO client receives them. Happy days.
>>
>> On my production servers, the job is queued in RabbitMq, processed
>> perfectly and the notification is published apparently. The problem is, it
>> doesn't appear to be received by the node amqp consumer 100% of the time.
>> Maybe 1 in 10 get delivered (and sometimes they don't look like the full
>> message). The rest just vanish.. It gets worse as we load the servers up.
>>
>> I thought it was the AMQP on the Node servers but I created a loop to run
>> MESSAGE_QUEUE 10,000 times and they were all consumed..
>>
>> So, I'm assuming the problem is that we're sending a message from within
>> another thread. At least, that's what I think it is. My knowledge of such
>> things has now come to an end...
>>
>> We've now replaced the last notification with Redis publish which works a
>> treat. But that's another cog to think about.
>>
>> Like I said, I'm new to this messaging / threading stuff,  and would
>> appreciate it if someone can point me in the right direction, tell me what
>> to read or suggestion something else to try. Or tell me to give up and go
>> home.
>>
>> Cheers
>>
>> Simon
>>
>>
>>
>>  Simon Morley
>> Big Chief | PolkaSpots Supafly Wi-Fi
>>
>> simon at PolkaSpots.com
>> 020 7183 1471
>> @polkaspots
>>
>>
>>
>>
>>
>>
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