[rabbitmq-discuss] [help] [beginner] server stops sending messages; publish (in transaction) hangs on commit

[Alistair Bayley]

On 24 February 2012 06:57, Simon MacMullen <simon at rabbitmq.com> wrote:
>
> The report you posted showed most memory in the VM being used by Erlang
> processes. You could run something like:
>
> rabbitmqctl eval
> 'lists:sublist(lists:reverse(lists:sort([{process_info(Pid,memory), Pid,
> process_info(Pid)} || Pid <- processes()])), 10).'
>
> to list the top 10 processes by memory use, along with some information for
> each one. This may tell us something interesting.

Just ran this:

$ sudo rabbitmqctl eval
'lists:sublist(lists:reverse(lists:sort([{process_info(Pid,memory),
Pid, process_info(Pid)} || Pid <- processes()])), 10).'

(wait for a bit - about 30s or so...)

Crash dump was written to: erl_crash.dump
eheap_alloc: Cannot allocate 153052320 bytes of memory (of type "old_heap").
Aborted
$

hmmm....


> Having said that, 100Mb for an idle server does not seem totally
> unreasonable - RabbitMQ is not optimised for small memory use when idle.

OK. Can I have some guidance as to how much memory we should allocate?
The ubuntu VMs we use have 256M by default; this is usually more than
enough for our needs. Is that enough for rabbitmq? Let's assume that
we have a small number of queues (6 or so) and the queues will contain
a small number (in the 100s) of fairly small messages (a few hundred
bytes each). The consumers are aggressive; messages should not remain
on queues for long, although they are persistent.

I don't see much in the docs about memory requirements. I think I'll
start by setting the vm_memory_high_watermark to 0, and seeing where
the memory use plateaus (assuming it does).

Also, I see from the tcpdump capture that the server does not send
back a response to the Tx.Commit, which presumably makes it difficult
for the client to detect that the message has not been accepted (other
than timeout). Indeed, the basic_publish returns nothing immediately,
although that could be a feature of the amqplib library. Is there an
option to get the server to return something that says that it is not
accepting messages?

Thanks,
Alistair