Hi,

After years without a single problem, I think I might have seen my first 
issue with beanstalkd.

The context :

We have a mecanism to control the flow of the messages. When we have "too 
much" messages in a queue from an ID or from a user, we put these messages 
in delayed state.

We experienced an unusual amount of messages in a queue from an ID. So 
almost all the messages in this queue was set to delayed over an extensive 
period of time. We will patch this control mecanism but it showed 
interesting things about beanstalkd :

- It generated a higher beanstalkd CPU usage (an expected behavior with 
more charge)
- As the messages were almost always set to delayed, lots of network IO 
were generated between application servers and beanstalkd server.
- After a while in this state (hours, days, it depends of the submitted 
load) : disk iowait reach 100% on the beanstalkd log disk, beanstalkd 
become unresponsive, the network IO stops immediatly.

Most of the time beanstalkd recovered by itself after 20 or 30 minutes of 
freeze/iowait @ 100%. But sometimes we had to stop watching the queue and 
restart beanstalkd to speed up the recovery.

The freeze/iowait period was very easy to predict. If the first freeze 
happened 20 hours after the submission of hundreds of thousands messages 
(which are flow controlled), the next one will happen in ~20 hours after 
recovery.

At first I thought it was a machine, docker or linux related problem but I 
reproduced the problem quite a few times :
- on a docker with Fedora 22 and beanstalkd-1.9-3.fc22.x86_64 over CoreOS, 
- on CentOS 6 and beanstalkd-1.9-2.el6.x86_64 on standalone machines (a 
medium sized AWS instance without SSD and a bigger one with SSD storage).


Here's the pattern of the problem, always the same :

Beanstalkd machine side :


​

Queue side 


​

We didn't try with last beanstalkd version as the changelog didn't reveal 
anything about this kind of problem.


Regards,


Arthur


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