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

[Simon Morley]

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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