[rabbitmq-discuss] Lightweight query for queues?

Sat May 7 20:02:57 BST 2011

On May 4, 2011, at 7:05 AM, Simon MacMullen wrote:

>> One useful thing about that thread was figuring out just how
>> resource-intensive the management plugin is when querying the API for
>> queues.  On my server with around 6000 queues, I can run 'rabbitmqctl
>> list_queues' and get results in a second, but if I query the API for
>> the list of queues it pegs one of the CPUs for upwards of 30 seconds,
>> returning over 8MB of data.
> 
> That seems really wrong. While the management plugin hasn't received much performance tuning it should in theory be capable of being faster than rabbitmqctl in such scenarios, since the management plugin maintains its own statistics database while rabbitmqctl has to go off and talk to each queue individually.
> 
> And indeed, for a trivial test (declare 6k empty queues, time rabbitmqadmin -f raw_json list queues > /dev/null), I get 1.9 seconds on my workstation. That should be improved (preliminary profiling suggests it's spending a lot of time *sorting* the list!), but I'm not sure why you're seeing something so much slower.
> 
> I know this would have been very slow prior to fixing the bug you encountered (due to writing very large error messages in the logs) - sorry if this is patronising but you're definitely seeing the slow response with the fixed version?

It's not patronizing, it always makes sense to double-check your assumptions. I'm pretty positive, when I look at my plugins directory I see the mem-fix version of the management plugin:

root at ip-10-242-73-123:/var/log/rabbitmq# ls /usr/lib/rabbitmq/lib/rabbitmq_server-2.4.1/plugins/
amqp_client-2.4.1.ez  rabbitmq-management-2.4.1-mem-fix.ez  rabbitmq-mochiweb-2.4.1.ez  webmachine-2.4.1.ez
mochiweb-2.4.1.ez     rabbitmq-management-agent-2.4.1.ez    README

> 
> Also, if you set force_fine_statistics to false for the rabbit_management_agent application - e.g with a /etc/rabbitmq/rabbitmq.config file like:
> 
> [{rabbit_management_agent, [{force_fine_statistics, false}]}].
> 
> - does it make any difference?

I tried that already and it didn't make any difference.  One big difference between your trivial test and my environment is that I have a few consumers on most of those queues, which adds a heck of a lot of data.

>> So, what I'd like to be able to do is:
>> 
>> 1. Allow specifying which data needs to be returned, so that more
>> expensive statistics can be avoided if necessary. 2. Allow filtering
>> the list of queues to return data for with a search term
> 
> <snip>
> 
>> Is this something you guys would consider?
> 
> Probably not (1) right now, since none of these statistics are supposed to be even slightly expensive, they should all just be hash lookups. (2) is somewhat interesting, probably simpler to implement and more generally useful. But I'd like to find out why you're seeing this run so slowly first.

Yeah, I wouldn't even bother with (1) except for the fact that it's so slow on my system.

Anything else I can do to try to find the cause?

Thanks,
Ian